164 technical Q&A on pumps

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1. What is a pump? Answer: A pump is a machine that converts the mechanical energy of a prime mover into the energy required to pump a liquid. 2. What is power? Answer: The work done per unit of time is called power. 3. What is apparent power? Excluding the energy losses and consumption of the machine itself, the actual power imparted to the liquid by the pump per unit time is called the useful power. 4. What is shaft power? Answer: The power transmitted by the motor to the pump shaft is called shaft power. 5. Why is it said that the power transmitted by the motor to the pump is always greater than the pump’s useful power? Answer: 1) While the centrifugal pump is in operation, some of the high-pressure liquid inside the pump flows back to the pump’s inlet, or even leaks outside the pump; as a result, some energy is lost ； 2) As the liquid flows through the impeller and pump casing, changes in flow direction and velocity, as well as collisions between fluid particles, also result in a loss of some energy ； 3) Mechanical friction between the pump shaft and the bearings and shaft seals also consumes a portion of the energy ； Therefore, the power transmitted by the motor to the shaft is always greater than the effective power of the shaft. 6. What is the overall efficiency of a pump? Answer: The ratio of the pump’s effective power to its shaft power is the pump’s overall efficiency. 7. What is the flow rate of a pump? What symbol is used to represent it? Flow rate refers to the amount of fluid (volume or mass) that passes through a certain cross-section of a pipe per unit time. The flow rate of the pump is denoted by “Q”. 8. What is the head of a pump? What symbol is used to represent it? Answer: Head refers to the increment in energy acquired by a unit weight of fluid. The head of the pump is denoted by “H”. 9. What are the characteristics of chemical pumps? Answer: 1) Can meet the requirements of chemical processing processes ； 2) Corrosion resistance ； 3) Resistance to high and low temperatures ； 4) Wear-resistant and erosion-resistant ； 5) Reliable operation ； 6) No or minimal leakage ； 7) Capable of transporting liquids in a critical state ； 8) It has cavitation resistance. 10. Into how many major categories are common mechanical pumps classified according to their working principle? Answer: 1) Vane pump. By rotating the pump shaft, various impeller blades generate centrifugal or axial forces on the liquid, thereby transporting it to pipes or containers; examples include centrifugal pumps, vortex pumps, mixed-flow pumps, and axial flow pumps. 2) Positive displacement pump. Pumps that use the continuous change in the volume within the pump cylinder to transport liquids, such as reciprocating pumps, piston pumps, gear pumps, and screw pumps ； 3) Other types of pumps. Such as electromagnetic pumps that use electromagnetic forces to transport liquid conductors ； Pumps that use fluid energy to transport liquids, such as jet pumps and air lifters. 11. What preparations should be made before maintaining chemical pumps? Answer: 1) Before maintaining machinery and equipment, it is necessary to shut down the equipment, cool it down, relieve pressure, and cut off the power supply ； 2) For machines and equipment that handle flammable, explosive, toxic, or corrosive substances, cleaning, neutralization, and substitution must be carried out prior to maintenance; work can only proceed after the relevant tests show satisfactory results ； 3) When maintaining equipment, machines, or pipelines that handle flammable, explosive, toxic, or corrosive substances or vapors, it is necessary to shut off the inlet and outlet valves for these materials and install blind flanges. 12. What process conditions must be met before maintaining chemical pumps? Answer: 1) Park ； 2) Cooling ； 3) Pressure relief ； 4) Cut off the power supply ； 5) Replacement 13. What are the general principles for mechanical disassembly? Answer: Under normal circumstances, one should start from the outside and move inward, from the top down, removing parts in sequence; for integral components, it is preferable to remove them as a whole whenever possible. 14. What are the power losses in a centrifugal pump? Answer: There are three types of losses: hydraulic loss, volumetric loss, and mechanical loss. 1) Hydraulic loss: When fluid flows within the pump, if the flow channels are smooth, the resistance is lower; if the channels are rough, the resistance is higher. Collisions and vortices that occur as the fluid enters the rotating impeller or exits it also result in losses. The above two types of losses are called hydraulic losses. 2) Volumetric loss: The impeller rotates, while the pump casing remains stationary; a small portion of the fluid in the gap between the impeller and the pump casing flows back to the impeller’s inlet ； Additionally, a portion of the fluid flows back from the balance hole to the impeller inlet, or leaks from the shaft seal. In the case of a multi-stage pump, some leakage also occurs from the balance disk. These losses are known as volume loss ； 3) Mechanical losses: When the shaft rotates, it experiences friction with bearings, packings, etc. The impeller also rotates within the pump casing, and its front and rear covers experience friction with the fluid. All these processes consume a certain amount of power. These losses caused by mechanical friction are collectively referred to as mechanical losses. 15. In production practice, what is the basis for balancing the rotor? Answer: Depending on the rotational speed and structure, either the static balancing method or the dynamic balancing method can be used. The static equilibrium of a rotating body can be solved using the static equilibrium method. Static balancing can only balance the imbalance of the center of gravity in a rotating body (i.e., eliminate moments), but cannot eliminate unbalanced couples. Therefore, static equilibrium generally only applies to disk-shaped rotating bodies with relatively small diameters. For rotating bodies with relatively large diameters, the problem of dynamic balance is often quite common and significant, so dynamic balance treatment is necessary. 16. What is balance? How are balances classified? Answer: 1) The process of eliminating imbalance in rotating parts or components is called balancing ； 2) Balance can be divided into static balance and dynamic balance. 17. What is static equilibrium? Answer: The method of determining the position in front of a rotating component where its imbalance lies, without the need for rotation, using specialized fixtures, while also allowing the determination of the location and magnitude of the balancing force to be applied, is called static balancing. 18. What is dynamic balance? Answer: Whenever rotation of a part or component takes place, it is necessary not only to balance the centrifugal force generated by the uneven weight distribution, but also to balance the couple moment resulting from that centrifugal force; this is what is known as dynamic balancing. Dynamic balancing is generally used for components that operate at high speeds and have large diameters, where extremely strict working precision is required; all such components must undergo precise dynamic balancing. 19. When performing static balancing on rotating parts, how is the location of the heavy spot on the part to be balanced determined? Answer: First, allow the part to roll freely several times on the balancing fixture. If it rotates clockwise on the last roll, the center of gravity of the part must be located to the right of the vertical center line (due to frictional forces). In this case, make a mark at the lowest point of the part using white chalk. Then, let the part roll freely again; if it rotates counterclockwise on the last roll, the center of gravity must be located to the left of the vertical center line. Make another mark using white chalk in that case. The positions indicated by these two marks represent the direction in which the weight is concentrated. 20. When performing static balance on rotating parts, how is the size of the counterweight determined? Answer: First, turn the heavier side of the part to a horizontal position, and then add an appropriate counterweight at the largest circle on the opposite, symmetrical side. When selecting a counterweight, it is necessary to take into account whether it will be possible to add or remove weight in the future, as well as whether the part remains level or only slightly swings after the counterweight is added. The part should then be rotated 180 degrees so that it stays level; this process should be repeated several times. Once the appropriate weight has been determined, it should be weighed to determine the exact gravity of the counterweight. 21. What are the types of mechanical rotor imbalance? Answer: static imbalance, dynamic imbalance, and mixed imbalance. 22. How to measure pump shaft bending? Answer: When the shaft bends, it causes imbalance in the rotor as well as wear on the moving and stationary parts. Place the small bearings on V-blocks, and the large bearings on roller supports; these V-blocks or supports must be secured firmly. Then, attach a dial indicator with its pointer pointing toward the axis center. Slowly rotate the pump shaft – if there is bending, the dial indicator will show a maximum and a minimum reading with each rotation, and the difference between these two readings indicates the maximum radial runout of the shaft, also known as deflection. The shaft bending is half of the runout; generally, the radial runout of a shaft should not exceed 0.05 mm in the middle and 0.02 mm at the ends. 23. What are the three main categories of causes for mechanical vibration? Answer: 1) In terms of structure: It is caused by manufacturing design defects ； 2) Installation aspect: Primarily caused by improper assembly and maintenance fitting ； 3) Operational aspects: Due to improper operation, mechanical damage or excessive wear. 24. Why is it said that rotor misalignment is an important cause of abnormal rotor vibration and premature bearing failure? Answer: Misalignment between rotors can occur due to factors such as installation errors, variations in rotor manufacturing, deformation under load, and changes in ambient temperature. In a shafting system with poor rotor alignment, the changes in stress on the coupling alter the actual working positions of the rotor journals and bearings. This not only affects the operating conditions of the bearings but also reduces the natural frequency of the rotor shafting. Therefore, rotor misalignment is a major cause of abnormal vibrations in the rotors and premature damage to the bearings. 25. What are the standards for measuring and checking the ellipticity and taper of journal surfaces? Answer: The ellipticity and taper of the sliding bearing shaft diameter measured during reinspection should meet the technical requirements; generally, they should not be greater than one thousandth of the diameter. The ellipticity and taper of the shaft diameter of rolling bearings shall not exceed 0.05 mm. 26. What precautions should be taken when assembling chemical pumps? Answer: 1) Is the pump shaft bent or deformed? ； 2) Is the rotor’s balance in compliance with standards? ； 3) Gap between the impeller and the pump casing ； 4) Is the compression amount of the mechanical seal buffer compensation mechanism sufficient? ； 5) Concentricity of the pump rotor and volute ； 6) Are the centerlines of the pump impeller flow channel and the volute flow channel aligned? ； 7) Adjustment of the clearance between the bearing and the end cover ； 8) Adjustment of the clearance in the sealing section ； 9) Is the assembly of the motor and the speed changer (accelerator/decelerator) in the transmission system in compliance with standards? ； 10) Alignment of the coupling’s coaxiality ； 11) Is the gap of the mouth ring in line with the standards? ； 12) Is the tightening force of the connection bolts in each section appropriate? 27. What is the purpose of machine pump maintenance? What are the requirements? Answer: Purpose: To eliminate the problems that have arisen from long-term operation by performing maintenance on the pumps. Requirements are as follows: 1) Eliminate or adjust the large gaps within the pump caused by wear and corrosion ； 2) Remove dirt, debris, and rust from inside the pump ； 3) Repair or replace components that do not meet the requirements or are defective ； 4) The rotor balance test passed ； 5) Check that the pump is coaxial with the drive unit and meets the standards ； 6) The trial run was successful, all documents are complete, and it meets the requirements for industrial production. 28. What are the reasons for excessive power consumption by mechanical pumps? Answer: 1) The total head does not match the pump’s head ； 2) The density and viscosity of the medium do not match the original design ； 3) The pump shaft is not aligned with the axis of the prime mover or is bent ； 4) There is friction between the rotating part and the fixed part ； 5) Impeller mouth ring wear ； 6) Improper installation of the seal or mechanical seal. 29. What are the causes of rotor imbalance? Answer: 1) Manufacturing errors: uneven material density, misalignment, out-of-roundness, and uneven heat treatment ； 2) Incorrect assembly: The center line of the assembled components is not aligned with the axis ； 3) Deformation of the rotor: uneven wear, and deformation of the shaft due to operation and temperature. 30. What is a dynamically unbalanced rotor? Answer: There exist rotors with equal magnitudes but opposite directions of unbalanced mass points, which combine to form two couples that are not on the same straight line. 31. How to prevent vacuum formation and cavitation during operation? Answer: When there is no space available: Gas and liquid are present inside the pump, preventing it from functioning; as a result, the flow rate and pressure drop to zero. Cavitation: It occurs within a pump that is in operation, resulting from changes in the flow rate and pressure of the fluid inside the pump, which leads to hydraulic shock. Generally, pumping vacuum in a pump refers to a cavitation phenomenon that occurs within the pump; vacuum caused by gas being drawn in due to installation issues or pipeline leaks is less common, with most cases resulting from operational and process changes. During operation, it is necessary to start by stabilizing the process conditions; the operating temperature should be set at its lower limit, and the same applies to pressure. To avoid or control cavitation, the pump flow rate must be kept at an appropriate level, in order to minimize significant fluctuations in pressure and temperature. Gas accumulation should be prevented in the pump’s suction line, and the inlet of standby pumps, which are under negative pressure, should be closed. 32. What are dynamic fit and static fit? What are their obvious differences? Answer: 1) Dynamic fit: a fit formed when the actual size of the hole is larger than the actual size of the pump ； 2) Clearance fit: a fit resulting from the actual size of the shaft being greater than that of the hole ； 3) Clear difference: Dynamic fit, allowing relative movement between the shaft and the hole ； Static fit: No relative movement occurs between the shaft and the hole. 33. What are the four basic requirements for equipment maintenance? Answer: Neat, clean, lubricated, safe. 34. What is the working principle of a labyrinth seal? Answer: Labyrinth seal: It consists of several annular sealing teeth arranged in sequence; these teeth create a series of throttling gaps and expansion spaces between them and the rotor. As the fluid passes through these complex pathways and undergoes multiple throttling processes, significant resistance is generated, making it difficult for the fluid to leak and thus achieving a sealing effect. 35. What is part interchangeability? What are its main functions? Answer: 1) The ability of parts to be exchanged for one another while still meeting the various performance requirements of the original parts is known as part interchangeability. 2) It mainly facilitates maintenance, reduces maintenance time, improves equipment utilization, and enhances work efficiency. 36. What is a dynamic pump? Answer: A dynamic pump continuously transfers energy to the liquid being pumped, increasing both its kinetic energy due to velocity and its potential energy due to pressure; primarily, the velocity of the liquid increases. Afterwards, the velocity is reduced, converting most of the kinetic energy into pressure energy, and it is this increased pressure of the liquid that is used for pumping. For example: 1) Vane pumps, which include centrifugal pumps, mixed-flow pumps, axial flow pumps, vortex pumps, etc ； 2) Jet pumps, including gas jet pumps, liquid jet pumps, etc. 37. What is a positive displacement pump? Answer: Positive displacement pumps transfer energy to the liquid being pumped through periodic changes in action and displacement, as they periodically alter the volume of the pump chamber; this causes the pressure of the liquid to rise to the desired level, thereby enabling transportation. Examples include: 1) Reciprocating pumps, such as piston pumps, plunger pumps, diaphragm pumps, and squeeze pumps ； 2) Rotary pumps, including gear pumps, screw pumps, Roots pumps, rotary piston pumps, vane pumps, crankshaft pumps, flexible rotor pumps, peristaltic pumps, etc. 38. What are the main performance parameters of a pump? Answer: It mainly includes aspects such as flow rate, head, net positive suction head, speed, power, and efficiency. 39. Why is it necessary to regularly turn the standby equipment? What should be noted when turning the gear? Answer: 1) Regularly turn the standby equipment manually; this is done to check whether the equipment operates smoothly and without any jamming ； Secondly, it prevents the bearing from bending or deforming, thus truly serving as a backup. 2) When turning the rotor, the following should be noted: first, the stopping position of the rotor after turning should be 180 degrees away from its original position ； Second, oil should be supplied to the pump that uses oil slinging for lubrication, and the shaft should be turned manually to prevent damage to the bearings. 40. What are the hazards of exceeding the rated current for a pump? Answer: The rated current is the current at which the motor can operate properly under rated voltage and rated power conditions. If this current is exceeded, the motor is prone to overheating, and the relay protection device will activate, causing the pump to stop. If the relay protection device does not function or fails to operate properly, it can lead to the motor being damaged and the pump being ruined. 41. What are the main aspects of routine inspection for mechanical pumps? Answer: 1) Check whether the readings on the pressure gauge and ammeter are within the specified range and remain stable ； 2) Check whether the operating sound is normal and if there are any abnormal noises ； 3) Are the temperatures of bearings, motors, etc. normal (not exceeding 60 degrees)? ； 4) Check whether the cooling water flow is unobstructed, and whether there is any leakage from the filler pump and mechanical seal; also determine whether such leakage is within acceptable limits ； 5) Check whether the connection parts are tight and whether the foundation bolts are loose ； 6) Check whether the lubrication is proper and whether the oil level is normal ； 42. What should the plant operators do when maintenance personnel arrive to carry out repairs? Answer: 1) Check whether the maintenance work order matches the equipment tag number of the device that is actually to be maintained ； 2) Contact the shift supervisor and have the dedicated electrician cut off the power ； 3) Provide maintenance personnel with information on the equipment damage and the specific areas that need repair ； 4) Cooperate with the maintenance work on site and supervise its quality ； 5) After the maintenance is completed, contact to restore power and conduct a test run ； 6) After normal operation is achieved, report to the on-duty shift leader and keep records. 43. What is the function of the inlet and outlet valves? Answer: 1) The pump inlet valve is a component used to isolate or disconnect the slurry pump from the system during maintenance; it cannot be used to regulate flow and should be kept fully open ； 2) The outlet valve is a component used to regulate flow rate and to isolate the pump from the system during startup, shutdown, and maintenance by shutting off the flow. 44. What determines the choice of seal for pumps used in chemical production? Answer: It is selected based on the process conditions, operating pressure, medium corrosion status, and rotational speed. 45. What are the types of flat gasket seals? Answer: 1) Non-metallic gasket sealing ； 2) Non-metallic and metallic composite gasket sealing ； 3) Metal gasket sealing. 46. What are the main causes of gasket leakage? Answer: 1) Leaks caused by design ； Improper selection of flange and flange sealing surface types ； b Improper selection of gaskets ； Improper selection of C-flange and bolt materials ； 2) Leaks caused by manufacturing, installation, and operation; a The machining precision of flanges and gaskets fails to meet technical requirements ； b When tightening the bolts, improper operation caused the gasket to become misaligned ； The sealing surface of the flange is dirty; there are impurities on it. 47. What is a mechanical seal? Answer: A mechanical seal, also known as a face seal, is a device that prevents fluid leakage by using at least one pair of faces perpendicular to the axis of rotation; these faces are pressed tightly together by fluid pressure and a compensation mechanism, allowing them to slide relative to each other. 48. How many common types of seals are used for pumps and machines? Answer: There are two types: dynamic seals and static seals. 49. What are the main causes of mechanical seal leaks? Answer: 1) Excessive wear occurs on the sealing surfaces between the rotating ring and the stationary ring; the load factor in the design is unreasonable, resulting in cracks, deformation, damage, etc., on the sealing surfaces. 2) Defects in several auxiliary seals or defects caused by improper assembly, as well as the selection of auxiliary seals unsuitable for the operating medium. 3) Insufficient spring preload, or after prolonged operation, the spring may break, corrode, loosen, or become coked. Additionally, suspended particles or crystals in the working medium may accumulate over time in the gaps between the springs, leading to spring failure. As a result, the compensating seal ring cannot move freely, causing leaks ； 4) Due to excessive deviation in the perpendicularity between the sealing surfaces of the rotating and stationary rings and the shaft centerline, the sealing surfaces fail to bond properly, resulting in leakage ； 5) Due to the large axial movement of the shaft and poor compatibility or quality of components related to the seal, leaks are likely to occur. 50. What factors determine the selection of materials for the mechanical seal friction pair? Answer: The choice should be based on factors such as the properties of the medium, operating pressure, temperature, and sliding speed; sometimes, the ability to withstand short-term dry friction during startup or when the liquid film is disrupted also needs to be taken into account. 51. What are the effective ways to increase the resistance of the medium in labyrinth seals? Answer: 1) Reduce the gap, 2) Intensify the vortex, 3) Increase the number of sealing teeth, 4) Try to convert the kinetic energy of the airflow into heat energy. 52. What is the working principle of floating ring seals? Answer: The floating ring seal relies on the throttling effect that occurs in the narrow gap between the shaft and the floating ring; sealing oil at a pressure higher than that of the gas is injected into this gap to prevent gas from leaking through. 53. What are the reasons for the increased leakage rate in floating ring seals? Answer: 1) Prolonged use of the floating ring leads to normal wear, which increases the gap ； 2) The bushing surface of the floating ring hole is rough and has low precision; wear over a short period of time increases the gap ； 3) Improper assembly leads to misalignment; the alignment fixtures come loose, allowing oil to leak out through other gaps, thereby increasing leakage ； 54. What is the function of the oil baffle? How to measure and adjust the oil shutoff gap? Answer: 1) The function of the oil baffle is to prevent the bearing lubricant from flowing along the shaft journal outside the bearing. There are two locations where the oil baffle can be installed: one on the bearing housing, and the other on the bearing shell ； 2) The oil baffle clearance can be measured with a measuring tool when the oil baffle is disassembled or assembled. For the bearing shells, the clearance in the oil baffle area can be adjusted to be a bit larger; however, the requirements for the clearance in the oil baffle area on the bearing housing are quite strict – generally, it should be 0.05–0.10 mm at the bottom, 0.10–0.20 mm on both sides, and 0.20–0.25 mm at the top. 55. What are the factors that affect labyrinth seals? Answer: 1) The radial clearance is too large, or the clearance of the newly installed air seal ring is too small; 2) The sealing sheets, air seal rings, or teeth become dull due to wear, or they deform when heated as a result of long-term wear, resulting in damage and rendering them unusable ； 3) After long-term use, the spring becomes loose and deformed, preventing the gas seal ring from settling in place. Over time, dust and debris accumulate, resulting in a sealing medium pressure that is lower than the working medium pressure or causing pressure instability. 56. What are the common types of dynamic seals? Answer: Bellows seal, expansion ring seal, spiral seal, pneumatic seal, hydraulic seal, centrifugal seal, packing seal, labyrinth seal, mechanical seal, etc. 57. What are the main factors affecting sealing? Answer: 1) The quality of the seal itself, 2) Process operating conditions, 3) Assembly accuracy, 4) Precision of the main machine itself, 5) Seal auxiliary systems. 58. What components does a mechanical seal consist of? Answer: A mechanical seal consists of a stationary ring, a rotating ring, a compensation and buffering mechanism, an auxiliary sealing ring, and a drive mechanism. The end faces of the stationary ring and the rotating ring are perpendicular to the pump’s axis and in contact with each other, forming a rotating seal surface. The stationary ring and gland, as well as the rotating ring and shaft, are all sealed using auxiliary sealing rings. These rings enable the sealing rings to move axially due to the action of the buffering mechanism, thereby keeping the end faces of the rotating and stationary rings in contact and compensating for wear on the end faces of the sealing rings. 59. What are the characteristics of mechanical seals? Answer: 1) It has good sealing performance; the leakage rate of mechanical seals is generally 0.01–5 ml/h. Depending on specific requirements, mechanically seals that are specially designed can have a leakage rate of as low as 0.01 ml/h, or even lower. In contrast, the leakage rate of packing seals is 3–80 ml/h (according to relevant Chinese regulations, it should be less than or equal to 3 ml/h when the shaft diameter is no larger than Φ50 mm, and less than or equal to 5 ml/h when the shaft diameter is Φ50 mm) ； 2) Long service life, generally over 8,000 hours ； 3) Low friction power, only 20%-30% of that of a packing seal ； 4) There is no relative motion between the shaft and the sleeve as well as the seals, so no friction is generated; the shaft and sleeve can remain in use for a long time ； 5) The sealing surface of the mechanical seal is perpendicular to the pump axis; when the pump shaft vibrates, the seal shifts accordingly. Therefore, as long as the vibration remains within a certain range, good sealing performance can still be maintained ； 6) The mechanical seal relies on the pressure of the sealing fluid and the force of the spring to keep the sealing surfaces of the stationary and rotating rings in contact; it also uses the spring force to compensate for wear. Therefore, once properly adjusted, the pump generally does not require frequent adjustments during operation, making it convenient to use with minimal maintenance needs ； 7) It has a wide range of operating conditions, and can be used in high-temperature, low-temperature, high-pressure, high-speed, and highly corrosive environments ； 8) Troubleshooting and part replacement are inconvenient, as maintenance can only be carried out after the vehicle has stopped ； 9) Complex structure with high assembly precision; assembly and installation require certain technical skills ； 10) The manufacturing cost is 60% higher. What are the main characteristic parameters of mechanical seals? Answer: 1) Shaft diameter: The shaft diameter range for pump mechanical seals is generally 6–200 mm; in special cases, it can reach 400 mm. The shaft diameter of a pump is usually determined based on strength requirements, and may be rounded off or adjusted using shaft sleeves to meet the standard shaft diameter requirements for mechanical seals ； 2) Rotational speed: It is generally the same as that of the pump; the rotational speed of centrifugal pumps is usually less than or equal to 3000 r/min ； High-speed centrifugal pumps: 8000 r/min or less; special pumps: 4000 r/min or less ； 3) Average circumferential velocity of the sealing surface: refers to the circumferential velocity of the average diameter of the sealing surface. The average linear velocity of the sealing surface has a significant impact on the heating and wear of the sealing surface (i.e., the friction pair). Generally, the circumferential linear speed for unloading sealed containers is less than or equal to 30 m/s ； The circumferential linear velocity of mechanical seals using spring-mounted stationary types is less than or equal to 100 m/s ； The special reachable speed is less than or equal to 150 m/s ； 4) End face specific pressure: The end face specific pressure Pc is the contact pressure exerted on the sealing surface (MPa). The end face specific pressure for end face sealing should be kept within a reasonable range; too low a value will reduce the sealing performance, while too high a value will increase heating and wear of the sealing cover. A reasonable end face specific pressure value for mechanical seals in pumps: for internal-mounted mechanical seals, Pc is generally set at 0.3–0.6 MPa; for externally mounted seals, Pc is set at 0.15–0.4 MPa. When the lubricity is good, the end-face pressure can be increased appropriately. For liquids with high viscosity, a higher end-face pressure is required; in such cases, Pc can be set at 0.5–0.7 MPa. For liquids that are volatile and have poor lubricity, a lower end-face pressure should be used, with Pc ranging from 0.3–0.45 MPa. 61. What are the checks to be performed before assembling a mechanical seal? Answer: 1) General inspection: It mainly checks the model, specifications, performance of each part, as well as its fit dimensions, and looks for any damages such as notches, pits, deformation, and cracks. 2) Inspection of the rotating and stationary rings: The sealing surface must be smooth and clean, free from defects such as chipped edges, pits, grooves, or scratches. For the graphite rings, they also need to be immersed to check for cracks. 62. How to check the parallelism, perpendicularity, and surface roughness of the end face? Answer: 1) End face flatness is 0.0006–0.0009 mm for liquid-phase media, and 0.0001–0.0004 mm for gas-phase media ； 2) Tolerance for balance: The deviation in the parallelism between the sealing end face and the contact surface of the sealing ring is generally such that it is 0.04 mm or less for the sealing ring. The parallelism deviation of the two end surfaces of the insert rings (ceramic rings and cemented carbide rings) should be less than or equal to 0.03 mm ； 3) Perpendicularity tolerance ； For the verticality deviation of the outer diameter centerline at the installation site of the sealing ring, the full diameter shall be less than or equal to 0.03 mm ； 4) Surface roughness: The hard material of the sealing surface (obtained by material removal) has a dull finish (achieved through grinding); the soft material (obtained by material removal) shows no signs of machining, with the direction of machining only barely discernible (achieved through grinding and precision turning). The area in contact with the auxiliary seal ring also has no signs of machining, with the direction of machining only barely discernible (achieved through grinding and precision turning), while the remaining areas show slight tool marks (achieved through turning and precision turning). 63. What are the requirements for inspecting the auxiliary sealing ring of a mechanical seal? Answer: 1) The surface of the auxiliary sealing ring should be smooth and flat, without any defects such as bubbles, cracks, or notches ； The end face dimensions must be uniform ； “The burr on the O-ring should ideally be at a 45-degree angle to the working surface ； 2) The hardness of the auxiliary sealing ring should be selected based on the pressure; higher sealing pressure requires greater hardness ； Those with lower sealing pressure have lower hardness. Synthetic rubber is commonly used for auxiliary sealing rings ； 3) The “O”-ring used to seal the cylindrical surface should have an inner diameter that is 0.5–1 mm smaller than the outer diameter of the sealing point. The inner diameter of the ‘O’-ring in the moving ring is relatively small, while the inner diameter of the ‘O’-ring in the stationary ring is smaller than that of the stationary ring itself ； 4) The compression amount of the auxiliary seal should be appropriate. Excessive compression can yield good sealing effects, but it also results in high frictional resistance, difficult assembly, and poor floating compensation capability during operation. The compression is too small; friction resistance is low. Assembly is easy, but the sealing effect is poor. The \"O\"-rings of the stationary and rotating rings in mechanical seals are both cylindrical surface seals, with a compression amount of approximately 8%-23% of the diameter of their cross-sectional flat surface. For those with a small diameter, use a percentage value ； For larger diameters, use a smaller percentage. 5) The compression amount of the \"O\"-ring must take into account its other functions. For a stationary ring without an anti-rotation pin, the \"O\"-ring serves both as a seal and to prevent rotation; therefore, it should be compressed to a greater extent to avoid the stationary ring from rotating and resulting in a failure of the seal. For the “O”-ring seal of the moving ring, under the premise of ensuring a good sealing effect, the compression amount should be kept small; this prevents excessive compression and resultant high resistance, which would hinder floating compensation. 64. What does the inspection of mechanical seal springs include? Answer: The inspection of springs includes: total number of coils, number of active coils, free height, whether the axis is perpendicular to the end faces, and the winding direction of the spring. However, for springs, the winding direction must be checked; for multiple springs, there’s no need to check the winding direction. For new springs, their original free height must be checked; this free height should be measured and compared with the original records. Springs with excessive residual deformation need to be replaced. After cleaning the old spring, its elasticity should be measured; if it has decreased by 20%, it needs to be replaced. For multi-spring mechanical seals, the difference in free height among the springs must be no less than 0.5 mm. 65. What are the requirements for inspecting the shaft and sleeve before installing a mechanical seal? Answer: 1) Check the fit dimensions, surface roughness, chamfers of the shaft (or sleeve), as well as the axial movement and radial runout of the shaft. In the case of a sleeve, examine the fit clearance between the shaft and the sleeve. The surface roughness of the shaft diameter (or shaft sleeve) on which the mechanical seal is installed should be 1.6 or less, and the axial play of the shaft must not exceed 0.25 mm. The shaft sleeve must not move axially; a certain amount of radial runout is allowed for the shaft or the shaft sleeve, as shown in the image: https://mmbiz.qpic.cn/mmbiz_png/HNDn8urPLxT3MPn2Wibic9hsa9kB8SJebZLkNsM6YLIw0LnibWs90vWQ19HjXicIJ383FvwxueibMDjb2m8holSxMUg/640?wx_fmt=png2). Check for wear on the shaft and the shaft sleeve. Due to mechanical vibrations and the compensatory movement of the moving ring, the shafts and bushings may also be worn by the \"O\"-ring seals; if wear occurs, they should be smoothed or replaced ； 3) The shaft sleeve housings and shaft sleeves should be in good condition. 66. What are the inspection items for the sealing end faces or sealing boxes? Answer: The roughness of the surface in contact with the static ring seal is 1.6; after the static ring is installed, the circular runout of its end face must not exceed 0.06 mm. The sealed end face or sealing chamber should be free of burrs, and the chamfer radius must be sufficient to ensure a smooth surface. The inner diameter of the sealed end face or sealing chamber should meet the requirements. 67. What are the “six fixed elements” of pump routine inspection? Answer: Conduct inspections by determining the route, personnel, timing, location, responsibilities, and requirements. 68. How many different types of maintenance are generally available for chemical industry pumps? Answer: There are mainly three forms: 1) maintenance and repair, 2) unplanned maintenance, 3) planned maintenance. 69. What are the precautions for installing auxiliary sealing rings? Answer: 1) Rubber auxiliary sealing rings should not be soaked or washed in gasoline or kerosene, to avoid swelling, deformation, and premature aging ； 2) The “O”-ring is installed on the stationary ring assembly; it should be aligned properly, without any twisting, as seen in its cross-section when the edges are free ； 3) When pushing the component, prevent damage to the “O”-ring. The main forms of damage include chipping, cracks, dents, curling, and twisting. 70. What are the causes of cracks in the “O”-ring of mechanical seals? Answer: The shaft surface is rough or has burrs ； The old shaft or bushing was damaged by the setting screws; it wasn’t polished smooth before assembly ； The edges of the keyway and anti-rotation pin slot are not properly trimmed. 71. What are the requirements for adjusting the spring compression amount of a mechanical seal? Answer: The mechanical seal spring is compressed by a certain amount by the drive screw; this amount is known as the spring compression. Once all the mechanical seals are installed, they are compressed further relative to the springs; this amount is known as the mechanical seal compression. The total compression amount of the mechanical seal spring is the sum of the compression amount caused by the drive screw and the elastic force of the spring itself. During assembly, the greater the compression of the mechanical seal, the smaller the force exerted by the spring on the moving ring. Therefore, regarding the working principle of mechanical seals, the size of the spring has a significant impact on their performance and lifespan; hence, the compression amount must be adjusted in accordance with the technical specifications during installation. 72. What are the precautions when installing the static ring assembly? Answer: 1) Insert the inspected static ring seal ring from the rear of the static ring, and fit the static ring assembly into the gland or sealing chamber. Under no circumstances should impact forces be applied to the mechanical seal parts or components. The compressed surface should be covered with clean cardboard or cloth to prevent damage to the sealed end face. 2) After assembling it into a rotating moving-ring assembly or a stationary static-ring assembly, press the compensation ring by hand to check whether it is properly installed and whether it moves smoothly ； Is the elastic opening positioned reliably? 3) Is the perpendicularity of the sealed end face to the center line of the shaft or sleeve within the required range? 4) For stationary mechanical seals, the anti-rotation pins of the stationary ring assembly must be properly positioned. When pushing the stationary ring assembly in place, the pin slots in the assembly should align with the pins. After it is pushed into position, the distance between the end face of the assembly and a certain end face of the sealing chamber should be measured to determine whether it has been installed correctly ； 5) When tightening the end cover with bolts, apply even and symmetrical force, tightening them in several steps rather than all at once, to avoid misalignment or even crushing the graphite ring. 73. What are the inspection requirements after the mechanical seal is assembled? Answer: After the mechanical seal is assembled, two inspections must be carried out. 1) Turntable inspection. Since the fluid has not yet been filled, there is only a very small amount of lubricating oil on the sealing surfaces of the stationary and rotating rings; therefore, it is not advisable to rotate the shaft too much to avoid damaging these sealing surfaces. 2) Fluid filling inspection. Check for any leaks; if there are no leaks, proceed with a trial run. 74. What are the inspection standards for dynamic seal leakage points? Answer: 1) The packing seal should not leak more than 15 drops per minute ； 2) The mechanical seal shall show no leakage at the initial stage, and no more than 15 drops per minute at the final stage ； 3) The gear oil pump allows slight leakage, not more than 1 drop per minute ； 4) Various oil lubricators are permitted to have a slight leak, but no more than 1 drop per minute. 75. What are the requirements for packing compressible packing materials? Answer: 1) The filler should be cut at a 45-degree angle, with the cuts pressed together vertically; the cut edges of adjacent layers should be offset by about 90 degrees ； 2) The packing should not be compressed too tightly. The gland bolts must be tightened symmetrically and evenly. The depth to which the gland is pressed in is generally equal to the height of one layer of packing, but should not be less than 5 mm. 76. What preparatory work should be done before packing mechanical installations? Answer: 1) Selection of packing: The selection should be based on the type of packing as well as the pressure, temperature, and corrosion characteristics of the medium. The medium compatibility, type, size, and performance of the packing must meet the requirements and standards of the equipment ； 2) Before installing the packing, the stuffing box should be cleaned, inspected, and trimmed; any damaged components should be replaced ； 3) Check the clearance fit between the shaft, gland, and packing. 77. What are the types of lubrication forms? Answer: 1) Oil drip lubrication, 2) Oil mist lubrication, 3) Splashing lubrication, 4) Pressure lubrication, 5) Dry oil cup lubrication ； 78. What factors should be considered when selecting lubricating oil? Answer: 1) Motion speed, 2) Nature of motion, 3) Operating temperature, 4) Pressure conditions, 5) Matching properties of the friction surfaces, 6) Surface roughness. 79. What are the functions of lubricants? Answer: 1) Cooling effect, 2) Rust prevention effect, 3) Temperature reduction effect, 4) Flushing effect, 5) Friction control effect, 6) Wear reduction effect, 7) Vibration damping effect, 8) Sealing effect ； 80. In what situations are calcium-based greases, sodium-based greases, and lithium-based greases suitable for use? Answer: 1) Calcium-based grease: It is water-resistant and can be used in humid working environments, but it is not resistant to high temperatures; the suitable operating temperature range is -10 to 60 degrees ； 2) Sodium-based grease: resistant to high temperatures, but not resistant to water; suitable for use in temperature ranges of -10 to 110 degrees ； 3) Lithium-based grease: It has heat resistance and water resistance; the applicable temperature range is -20 to 1200 degrees ； 81. What are the “five fixings” in the management of lubricating oil for pumps? Answer: For pumps, it is necessary to ensure fixed locations, scheduled maintenance, use of appropriate quality lubricants, correct quantities, and designated personnel for inspections and oiling, so as to guarantee their normal operation ； 82. What is the basic principle behind the importance of lubrication for pumps? Answer: Lubricants can adhere firmly to the friction surfaces of mechanical parts, forming an oil film. This oil film bonds strongly with those friction surfaces; the two surfaces in contact are separated by the lubricant, turning the friction between the mechanical parts into friction between the lubricant molecules. This helps to reduce friction and wear, thereby extending the service life of the mechanical parts. 83. What are the reasons for oil leakage in pumps lubricated with engine oil? Answer: 1) The oil level is too high, causing oil to leak from the inner holes of the bearing caps at both ends of the bearing housing ； 2) Oil leakage at static sealing points, such as leakage caused by a clogged oil drain thread ； 3) Oil leakage at the interface between the bearing cover and the bearing ； 84. What role does the lubricant play during the rotation of bearings? Answer: 1) Lubrication, 2) Cooling, 3) Cleaning, 4) Rust prevention, 5) Sealing, 6) Shock absorption and vibration reduction, 7) Friction and wear prevention ； 85. What are the main properties of lubricating oils? Answer: Acid value, viscosity, viscosity index, flash point, mechanical impurities, freezing point, residue, ash content. 86. How many methods are there for measuring the clearance of radial sliding bearings? How to measure using the axis-lifting method? Answer: There are three common methods: the lead pressing method, the shaft lifting method, and the fake shaft method. Shaft lifting method: A dial indicator is installed at the part of the shaft diameter that is close to the bearing shell; another dial indicator is placed on the top of the outer shell of the bearing shell for monitoring. The shaft diameter is gently lifted until it makes contact with the upper bearing shell, but care must be taken not to cause excessive movement of the upper bearing shell. The reading from the dial indicator on the shaft diameter, minus the amount of movement of the upper bearing shell, gives the bearing clearance. 87. What are the faults of sliding bearings? How to deal with it? Answer: Fault: Gluing. Remedial measures: 1) Ensure the correct installation position and proper clearance requirements, 2) Ensure proper lubrication of the rotor. Failure: Fatigue fracture. Remedial measures: 1) Keep the bearing surface smooth, 2) Ensure good balance of the rotor. Fault: Wear. Remedial measures: 1) Avoid insufficient lubrication, 2) Clean the lubrication system promptly. Fault: Scratch. Remedial measures: 1) Prevent sudden fuel cutoff, 2) Avoid impact during installation or removal. Fault: Scratching. Remedial measures: Pay attention to keeping the oil circuit clean to prevent dirt from entering. Fault: Pitting. Remedial measures: 1) Increase the oil supply pressure, 2) Modify the shape of the oil grooves and channels in the bearing shells, 3) Reduce the bearing clearance. Fault: Electroerosion. Remedial measures: 1) Ensure the machine’s insulation condition and protective devices are in good order, 2) Ensure proper grounding of the machine ； 3) Check the shaft diameter; if pitting due to electroerosion appears on it, grind the shaft diameter to remove the pits. 88. What are the reasons for adhesion in sliding bearings during use? Answer: 1) Bearing overheating, 2) Excessive load, insufficient oil volume, 4) Improper operation or malfunctioning temperature control. 89. What are the reasons for abnormal noises when a rolling bearing is in operation? Answer: 1) Severe separation of the rolling elements or raceways, resulting in an uneven surface. 2) The bearing accessories are not installed properly, resulting in looseness or friction. 3) There are iron shavings or dirt inside the bearing. 4) Lack of lubricant. 90. What are the types of radial clearance in rolling bearings? Answer: 1) Original clearance: The clearance in the free state before bearing installation. 2) Fit clearance: The clearance existing after the bearing is installed on the shaft or in the hole; its size is determined by the degree of interference, and this fit clearance is smaller than the original clearance. 3) Clearance at operation: In some bearings, due to their structural characteristics, the clearance can be determined during assembly or use by adjusting the relative positions of the bearing rings, as is the case with radial thrust ball bearings. 91. What considerations should be taken when selecting rolling bearings? Answer: 1) The direction and nature of the load. 2) Requirements for self-aligning performance. 3) Bearing speed. 4) Cost-effectiveness. 5) Level of accuracy. 92. How to choose the lubrication method for rolling bearings? Answer: The proper operation of bearings is related to lubrication; dry oil lubrication is used when the temperature of the medium being transported is 80 degrees and the rotational speed is below 2950 r/min ； When the temperature of the conveying medium exceeds 80 degrees and the power is high, thin oil lubrication is used. 93. How to check the condition of rolling bearings? Answer: The surfaces of the rolling elements and raceways must be free from defects such as spots, dents, peeling, or flaking. It should rotate smoothly; when turned by hand, it should slow down gradually and come to a stop smoothly, without stopping suddenly or experiencing any vibrations. There should be a certain gap between the cage and the inner and outer rings; this can be tested by pushing the cage radially with the hand. The clearance is within the standard range, as measured by the lead compression method. 94. What precautions should be taken when assembling and disassembling rolling bearings? Answer: 1) The force application point must be correct; the principle is to fit the inner ring with the shaft and the outer ring with the housing, in order to prevent the rolling elements and raceways from deforming or getting damaged due to stress. 2) The force should be applied symmetrically; it is not allowed to strike only one side, as this can cause the bearing to shift and damage the shaft journals. 3) Before disassembly and assembly, the shaft and bearings must be cleaned thoroughly; there should be no rust, burrs, or similar impurities. 95. What problems can occur if there is too much oil in the bearing housing? Answer: Excessive oil filling in the bearing housing leaves no space for heat dissipation, which can cause the bearings to overheat. 96. How to check the radial clearance of rolling bearings? Answer: Measurements are taken using the lead compression method and the feeler gauge method. The radial clearance is not indicated in the bearing code; the clearance of a bearing varies depending on its inner diameter, and this value is determined by referring to tables. Under normal circumstances, the radial clearance of rolling bearings should not exceed 0.3% of the bearing’s inner diameter, while the radial clearance of cylindrical bearings should not exceed 0.2% of the bearing’s inner diameter. 97. Why is preloading necessary for rolling bearings? Answer: When assembling radial thrust ball bearings or radial ball bearings, if an axial load is applied to the inner and outer rings of the bearing, these rings will move relative to each other, thereby eliminating the gaps between the rings and the rolling elements and causing initial elastic deformation. Preloading can improve the rotational accuracy and lifespan of the bearing as well as reduce shaft vibration. 98. How to achieve preloading of rolling bearings? Answer: 1) Pre-tensioning is achieved through the difference in thickness between the inner and outer washer rings of the bearing. 2) Pre-tensioning is achieved using a spring; the force exerted by the spring on the outer ring of the bearing enables pre-tensioning of the bearing. 3) Narrowing the inner or outer rings used in pairs to achieve preloading. 4) Adjust the axial position of the inner ring in the tapered bore of the bearing to achieve preloading. 99. What are the substitution principles for rolling bearings? Answer: 1) Technical parameters such as the service capacity factor of the bearing and the allowable static load should be as equal to or higher as possible than those of the originally installed bearing. 2) The allowable maximum speed should be selected to be equal to or higher than the actual speed of the originally installed bearings. 3) The precision grade of the replacement bearing should not be lower than that of the original bearing. 4) The dimensions must be the same; the dimensions of the machine that match those of the bearing should not be changed arbitrarily just because a bearing is being replaced. 5) For bearings that use a nested design, it is necessary to ensure the concentricity of the inner and outer cylindrical surfaces, and the appropriate tolerances and fits must be selected. 100. What are the various fixing methods for rolling bearings? Answer: 1) Unilateral loading with bilateral fixation, 2) Bilateral loading with unilateral fixation, 3) Mixed fixation. 101. What determines the bearing oil level? Answer: For rolling bearings, the lowest line of the ball centers represents the normal oil level; the lower one-third of the balls indicates a low oil level, while the upper two-thirds above the line of the ball centers signifies a high oil level. In the case of lubrication systems using oil rings for spindles, these oil rings are generally 1.5 to 2 times larger in diameter than the spindle they are meant to lubricate. The oil level in the oil chamber should be at a certain distance from the spindle oil; this distance is generally half of the spindle diameter, or about 5 mm below the bearing surface at the highest oil level. 102. Why is it not good if the bearing oil level is too high or too low? Answer: 1) The bearing oil level is too low, resulting in some parts of the bearing not being lubricated; this causes wear and heating in the bearing, leading to its damage. 2) The oil level is too high; as the spindle rotates, the rolling bearings and oil rings are prone to leaking oil from the shaft seal during the oil-carrying process ； An excessively high oil level also hinders the rotation of the oil ring, causing the bearings to overheat. 103. What are the requirements for filling the oil amount in bearings lubricated with grease? Answer: 1) For machinery operating at low speeds (speeds below 1500 r/min), the amount of oil filled is generally not more than two-thirds of the entire bearing chamber ； 2) For machinery with a rotational speed of over 1500 r/min, the amount of oil filled should generally not exceed half of the total volume of the bearing chamber. 104. What are the reasons for high bearing temperatures? Answer: 1) If the oil level is too low, the amount of oil entering the bearings decreases. 2) Poor oil quality, ingress of water or impurities, oil emulsification and deterioration ； 3) The oil ring does not rotate, resulting in a disruption in oil supply to the bearing. 4) Insufficient cooling water for the bearings 5) Damaged bearings 6) Excessive or insufficient tightening force applied by the bearing caps, which eliminates the radial clearance and reduces flexibility. 105. What are the requirements for the properties of bearing bush materials in sliding bearings? Answer: 1) It should have sufficient strength and plasticity, so that the bearing liner can withstand a certain working pressure and distribute the pressure evenly between the shaft journals. 2) It has good swelling properties and wear resistance. 3) Good lubrication and heat dissipation performance. 4) It should have good processability. 106. What material should be used to manufacture the bearing shells of sliding bearings? Answer: Cast steel, forged steel, cast iron 107. Based on experience, what is the typical radial clearance for bearing shells? Answer: For bearings with different structural forms, the shaft diameter can be taken as one thousandth to three thousandths thereof. 108. What is the impact of the clearance size in sliding bearings? Answer: 1) The gap is small, resulting in high precision; however, if it is too small, lubrication cannot be ensured, and no oil film can be formed. 2) The gap is large, precision is low; it is prone to vibration during operation, and the oil film is unstable. 109. What are the items included in bearing bush inspection? Answer: 1) Is the position of the friction marks on the journal surface of the tungsten alloy correct, and have the scratches left by the lapping tool there been polished or worn away? 2) Check whether there are any scratches, damage, or corrosion on the tungsten gold surface. 3) Tungsten gold has numerous cracks, local peeling, and delamination (which can be detected by tapping with a wooden stick or using the oil immersion method). 4) Check for wear and corrosion on the load-bearing surface of the shims or on their spherical surfaces, whether the shim screws are loose, and whether the shims are in good condition. 110. What are the advantages of tilting pad bearings? Answer: The advantage of tilting pads is that each pad can swing freely, allowing for the formation of an optimal oil film under any circumstances. They also exhibit good stability at high rotational speeds and are less prone to oil film oscillation. 111. What kind of bearing positions constitute defective bearings? Answer: 1) Loss of original rotational precision, 2) Noise during operation, 3) High rotational resistance. 112. What are the causes of overheating in the rolling bearings of centrifugal pumps? Answer: 1) Small axial clearance in the rolling bearing; 2) Incorrect installation direction; 3) Dry friction or looseness; 4) Poor quality of lubricant, insufficient amount of oil, or poor circulation; 5) Deformed oil slinger that fails to carry oil. 113. What are the criteria for discarding rolling bearings used in pumps (centrifugal ball bearings)? Answer: 1) The inner and outer raceways are stripped, severely worn, or cracked. 2) The rolling elements are out of round or have surface spalling, along with cracks. 3) The cage is severely worn or deformed, and cannot hold the rolling elements in place. 4) There is noise or vibration during rotation; upon stopping, there is braking and reverse rotation. 5) The fit clearance of the bearing exceeds the maximum allowable clearance value. 114. What causes the fish-scale-like peeling to occur on the raceway surfaces of the inner and outer rings of a bearing, or on the rolling surfaces of the rolling elements? Answer: 1) Excessive load, 2) Improper installation, 3) Presence of foreign objects, inappropriate lubricant, 4) Inappropriate bearing clearance, 5) Poor precision of the shaft and bearing housing, uneven rigidity of the bearing housing, high deflection of the shaft, 6) Rust, erosion, scratches, and indentations. 115. What are the performance aspects of bearing alloys? Answer: 1) Low friction coefficient, reducing shaft wear ； 2) High plasticity, enabling good running-in of the shaft and bearing shells ； 3) Good thermal conductivity ； 4) Sufficient compressive strength and fatigue strength. 116. What properties should high-speed rotating sliding bearings possess? Answer: 1) It should be able to withstand radial and axial loads ； 2) A low coefficient of friction is also required ； 3) Long service life and excellent performance in terms of stable and reliable operation. 117. What are the causes of vibration in rolling bearings? Answer: 1) Random vibrations transmitted by the rolling elements. 2) Random vibration occurred due to improper installation and lubrication. 3) Vibration transmitted from outside the bearing. 118. What are the assembly requirements for rolling bearings? Answer: 1) The end face of the bearing marked with the model number should be located in a visible area to facilitate replacement. 2) The radius of the arc at the journal or housing hole shoulder should be smaller than the radius of the arc fillet on the bearing surface, to ensure that the bearing fits tightly against the shoulder and the housing hole shoulder after assembly. 3) The bearing fixing device must be in good condition and reliable, with an appropriate level of tightness and secure loosening. 4) Maintain cleanliness during assembly to prevent debris from entering the bearings ； 5) After assembly, the bearing rotates smoothly without noise, and the normal temperature rise does not exceed 50 degrees. 119. What are the common bearing material options for sliding bearings? What are their respective features? Answer: 1) Gray cast iron, which is used in applications with low speeds, light loads, and no impact loads; common grades include HT15-33 and HT20-40. 2) Copper-based bearing alloys. Commonly used materials include ZQSn10-1 phosphor-tin bronze and ZQA19-4 aluminum bronze, which are suitable for operation under conditions of medium speed, high turbidity, and impact loads. 3) Oil-impregnated bearings: These are generally porous materials formed by compressing bronze or cast iron powder along with an appropriate amount of graphite, followed by high-temperature sintering. It is commonly used in low or medium speed applications with light loads and in situations where lubrication is difficult. 4) Nylon. Commonly used types include nylon 6, nylon 66, and nylon 1010. Nylon bearings offer advantages such as good running properties, soft debris produced upon wear that does not damage the shaft journals, and good corrosion resistance; however, they have poor thermal conductivity and expand when exposed to water. 5) Bearing alloy (Babbitt alloy). It is an alloy of tin, lead, copper, antimony, etc., with good wear resistance, but lower strength; it cannot be used alone to make bearing shells, and is usually cast onto bearing shell matrices such as bronze, cast iron, and steel. 6) Material for the three-layer load-bearing bearing. There are two commonly used types: polypropylene fluorovinyl steel body composite materials and polyoxymethylene steel body composite materials. 120. What are the reasons for excessive temperature rise in rolling bearings? Answer: 1) During installation and operation, impurities or dirt get inside. 2) Inappropriate lubricants are used or insufficient lubricant is applied. 3) Friction occurs due to friction between sealing devices, heat rings, bushings, etc., or due to loose fitting. 4) Incorrect installation, such as skewing of the inner and outer rings, misalignment of the mounting hole, deformation of the raceways, and improper adjustment of the clearance. 5) Incorrect selection – using an inappropriate bearing as a substitute can lead to overheating due to overload or excessive speed. 121. Centrifugal ball bearings are installed on the shaft; how should the tapping method be applied in such cases? Answer: Use a steel sleeve, copper sleeve, or copper rod to strike the bearing ring symmetrically, pressing it evenly into the designated position. It is prohibited to strike the outer ring of the bearing to avoid damaging it. After installation, check that the outer ring of the rotating bearing moves freely without any obstruction. 122. What are the common methods for removing rolling bearings? Answer: tapping method, pulling method, pushing method, thermal disassembly method. 123. What precautions should be taken when removing rolling bearings (with the bearings on the shaft) using the tapping method or the pulling method? Answer: 1) The striking force should generally be applied to the inner ring of the bearing; it should not be applied to the rolling elements or the cage, and striking the outer ring of the bearing is not allowed. 2) When using the pulling method, the inner ring of the bearing should be held, rather than only the outer ring, to prevent excessive loosening or damage to the bearing. 124. How should a dial indicator be installed when using the shaft-lifting method to measure the clearance in a sliding bearing? Answer: Install the bearing, but do not tighten the bolts. Place a dial indicator on the back of the upper bearing shell and another one on the shaft diameter. Gently lift the shaft, but not too much, until the pointer of the dial indicator on the back of the upper bearing shell moves. 125. What are the assembly requirements for split-type centrifugal sliding bearings, bearing covers, and bearing housings? Answer: During assembly, the back of the bearing shell should make good contact with the cover and the seat hole; the contact area must be at least 40%-50% of the total area, and there should be no gaps anywhere, otherwise grinding will be required. The fixing pins and screws used to secure sliding bearings should have their ends buried 1-2 mm within the bearing body. The various gaskets used in the Japanese-style design should have the same shape as the tile joints, and their width should be 1 mm less than that of the inner side of the bearing. The gaskets should be flat without any sharp edges, and the thickness of the gaskets on both sides of the joint should be consistent. 126. How to adjust the clearance of a split-type centrifugal sliding bearing? Answer: 1) Adjust the shims at the joint surface to ensure that the top and side clearances between the shaft and the bearing shells meet the required values. In the absence of specific regulations, experience suggests a value of between one thousandth and two thousandths of the journal diameter; this range should be selected based on the speed, load, and lubrication conditions. 2) The side clearance is generally half of the top clearance. 3) If the structure does not allow the use of shims, the gap must be adjusted by grinding the edges of the upper bearing shells. While adjusting the clearance of the tile joints, it is also necessary to ensure that the upper and lower tile joints fit tightly together, with a gap not exceeding 0.05 mm. 127. What are the main types of damage to rolling bearings? Answer: 1) Fatigue pitting, 2) Scratches, 3) Burns, 4) Electroerosion, 5) Retainer damage, 6) Breakage of the inner and outer rings, 7) Ball out-of-roundness, 8) Raceway surface delamination. 128. What are the characteristics of key joining? Answer: Torque is transmitted via the sides of the key; it only provides circumferential fixation for the components on the shaft and cannot withstand axial forces. If axial fixation is required, fixing elements such as screws or retaining rings must be used. 129. What are the assembly requirements for loose-key connections? Answer: For regular flat keys, semi-circular keys, and guide keys, after assembly there should be some interference on both sides of the key; a certain gap must remain on the top surface of the key, while the bottom surface of the key should be in contact with the bottom surface of the shaft groove. For sliding keys, the side key is in contact with the bottom surface of the groove, while there is a gap between the key and the bottom surface of the shaft groove. 130. What are the steps for preparing a loose-key connection? Answer: 1) Remove burrs from the keys and keyways. 2) File the key to the appropriate length, leaving a gap of about 0.1 mm between the key head and the shaft slot. 3) Fit the key head with the keyway; for ordinary flat keys, flat round keys, and guide keys, the key should fit snugly within the shaft slot, while slip keys should fit within the gear slot. 4) Apply oil to the mating surface, and install the key on the shaft using a copper rod or a hammer with a padded handle. 131. What are the precautions for installing and removing ordinary flat keys and shaft grooves? Answer: Before installation, check and remove any burrs or edges from the keyway; verify the straightness of the key. A gap of 0.1 mm should be left between the key head and the keyway, and oil should be applied to the mating surfaces before pressing the key into the keyway. Before removal, the key should be gently tapped or shaken to loosen it, and then removed using a small flat tool or screwdriver starting from the head end of the key; it is strictly prohibited to strike or remove it from the side where it fits. 132. What are the requirements for the fit between keys and shafts? Answer: 1) The fit between the key and the keyway should be perfect with no issues on either side; generally, there should be a gap of 0.1–0.4 mm at the top. 2) Do not use padding or twisting to increase the tension of the key. 133. What are the four types of deviation in coupling alignment analysis? Answer: concentric and parallel, concentric but not parallel, parallel but not concentric, not concentric and not parallel. 134. What is point method measurement? Answer: The method of simultaneously measuring the axial and radial clearances at a certain position of the coupling from the same point is called the one-point measurement method. 135. What is the principle of coupling alignment? Answer: Aligning a coupling involves primarily measuring its radial and angular displacement. When the two shafts are not on the same axis, a relative deviation arises between the outer rings or end faces of the couplings. The deviation of the shaft axes can be calculated based on these measured values. To obtain accurate results, it is necessary to rotate both rotors by the same angle, ensuring that the relative position of the measurement points on the coupling can change; this helps to eliminate errors caused by uneven surfaces on the coupling or by axes that are not perpendicular to each other. 136. What are the prerequisites for aligning a coupling? Answer: 1) The axis of the coupling coincides with the axis of the rotor. 2) Both the journal and the outer diameter of the coupling are perfectly circular. 3) The end face of the coupling is perpendicular to the axis. 4) Before aligning the coupling, it is necessary to first measure its radial and end-face runout, as well as whether the runout of the shaft journals meets the requirements. 137. What are the requirements for coupling assembly? Answer: Strictly ensure the coaxiality of the two axes, so that no unilateral loading occurs during operation, thereby maintaining balance and reducing vibration. 138. What are the methods for aligning couplings and measuring radial and angular displacement? Answer: 1) Use support and feeler gauges for measurement. 2) Measurement using a center gauge and feeler gauge. 3) Measurement using a center gauge and dial indicator. 139. How does a safety valve work? Answer: A safety valve is a valve that opens and closes automatically based on the working pressure of the medium. When the working pressure of the medium exceeds the specified value, the safety valve automatically opens its disc, allowing the excess medium (gas) to be discharged. When the pressure returns to normal, the valve disc closes automatically again. 140. What are the requirements for valve assembly? Answer: 1) Conditions for assembly: All valve components must be cleaned, inspected, repaired, or replaced, and their dimensional accuracy, positional accuracy, surface finish, as well as mechanical properties such as material quality and heat treatment characteristics must meet the technical requirements before they can be assembled. 2) Assembly principles: Generally, disassemble what was assembled first and then assemble what was disassembled last; understand the nature of the fit between components. Avoid forceful banging or random handling; follow a systematic approach – start from the inside out, from bottom to top, beginning with the easier tasks before moving on to more difficult ones. Assemble the parts, components, and mechanisms first, and then proceed to testing with the cover on. 3) Assembly quality: Proper fit, correct connections, complete valve components, tightened bolts, smooth operation, accurate indication, reliable sealing, and suitability for the operating conditions. 141. What are the inspection methods for valve quality? Answer: 1) Visual inspection. 2) Dimensional inspection. 3) Assembly inspection. 4) Disassembly inspection. 5) Pressure test inspection. 142. Into how many categories are valves classified based on their structural features? Answer: 1) End-type, 2) Gate-type, 3) Plug-type, 4) Butterfly-type, 5) Screw-up type, 6) Slide valve-type. 143. What are the basic parameters of valves? Answer: 1) The nominal diameter of the valve, 2) The nominal pressure of the valve, 3) The relationship between the operating pressure and operating temperature of the valve, 4) The medium used in the valve. 144. What are the characteristics and uses of gate valves? Answer: 1) Advantages: It has better sealing performance than globe valves, lower fluid resistance, requires less effort to open and close; the sealing surface is less subject to erosion by the medium when fully open, it is not restricted by the flow direction of the medium, it can handle two flow directions, has a shorter structural length, and offers a wide range of applications. 2) Disadvantages: It has a large external dimension, requires sufficient space to be opened, takes a long time to open and close; the sealing surfaces are prone to erosion and scuffing during opening and closing, and the two sealing pairs pose difficulties in processing and maintenance. 3) Applications: Gate valves are generally used in pipes and equipment with diameters ranging from DN15 to 1800 mm. They are widely used, primarily for shut-off purposes; they must not be used for throttling. 145. What are the functions of valves? 1) On/off function, 2) Regulation function, 3) Throttling function. 146. What precautions should be taken when installing a globe valve? Answer: 1) Due to the asymmetrical inlet and outlet of the stop valve, during installation the medium should flow through the valve opening from bottom to top, that is, with the inlet at the lower level and the outlet at the higher level, so as to make it easier to open the valve and prevent leakage from the packing. It truly serves to cut off and regulate pressure and flow. 2) If the stop valve is installed in the reverse direction, the inlet pressure will be exerted on the flange and packing areas in the middle of the valve body. Since the design pressure for these two areas is relatively low, it may lead to leaks at the middle flange and packing of the valve body. 147. What are the general requirements for valve installation? Answer: 1) Before installing the valve, the inside of the pipeline should be cleaned thoroughly to prevent iron oxide particles, welding slag, hard particles, or other foreign objects from scratching the valve’s sealing surface. At the same time, carefully check and verify the model specifications of the valves, as well as ensure that they are closed tightly. 2) For valves with a directional requirement, pay attention to the installation direction and do not install them in the reverse order. 3) Due to the asymmetry of the valve chamber of the stop valve, after installation, the fluid flows from bottom to top through the orifice. 4) Gate valves should also not be installed upside down, as this will cause the medium to remain in the valve chamber for an extended period, leading to corrosion of the valve stem. Straight-stem gate valves should not be installed at the bottom to prevent rusting of the wheel post. 5) Check valves are divided into lift-type and swing-type categories. Lift-type check valves can only be installed horizontally, while swing-type check valves must have their pivot pins installed horizontally. Swing check valves can be used in horizontal and vertical pipes. 6) It should generally be installed in a closed state. 7) When installing or replacing heavier valves, the lifting latch should not be tied to the handwheel or valve stem, but rather to the valve body, in order to avoid damaging components such as the handwheel or valve stem. 8) When installing a pressure relief valve, shut-off valves and pressure gauges should be installed before and after it, with a safety valve placed after the valve. 148. What are the main types of directional valves? Answer: Valves with a directional function mainly include globe valves, throttle valves, pressure relief valves, check valves, etc. 149. What is the process for testing the strength of valves (hydrostatic test)? Answer: 1) Fill the valve with water and then drain the air inside. 2) The valve is in the open position. Raise slowly to the test pressure. 4) After reaching the test pressure, maintain it for more than 5 minutes; there should be no leaks at the gland cover of the casing. 150. How should a safety valve be transported to the site for installation after calibration? Answer: After the safety valve is calibrated, it should be sealed with a lead seal. It must remain in an upright position during transportation and installation, and contact with other objects is strictly prohibited to ensure the accuracy of its calibration. 151. For a Z41H-25 gate valve with DN80 size, where the valve cover is of M16 size and the packing gland uses M12 bolts, and disassembly is required for maintenance and replacement of the packing and valve cover gaskets, what tools are needed? Answer: One adjustable wrench of 250-300mm, one 24-27mm ratchet wrench, one 17-19mm ratchet wrench, one 8-inch screwdriver, one 1.5P hammer, and one flat scraper. 152. What tests should be conducted during valve inspection? Answer: First, a hydrostatic strength test is conducted, and then its airtightness is checked. 153. What do Z44B-16, DN150 mean? Answer: Z-gate valve ； 4-Flange connection, 4-Planar double gate ； B-babbitt seal ； 16-Nominal pressure 1.6 MPa ； DN150 – nominal diameter of 150 mm. 154. What do A41T-10, DN100 mean? Answer: A - Safety valve ； 4-Flange connection ； 1-Angle pose ； The T-seal surface is a copper mouth ； 10-Nominal pressure 1.0 MPa ； DN100 – nominal diameter of 100 mm. 155. What is assembly? How many steps are there in the general assembly process? Answer: In the production process, the process of connecting the parts that have passed inspection, in accordance with the specifications in the drawings and technical requirements, through various methods to form components and sub-assemblies, which ultimately make up a complete machine, is called assembly. The assembly process can generally be divided into component assembly, subassembly, and final assembly. 156. How is the work divided during assembly? Answer: For components that require heating and are relatively large, along with their smaller mating parts, it is more appropriate to use cold assembly due to the limitations of the heating equipment. There are also parts with special materials or those that require high precision after assembly and need an extremely small degree of deformation, for which cold fitting is necessary. 157. How is the assembly work divided? Answer: 1) Assembly of components, 2) Assembly of parts ； 3) Final assembly, 4) Final assembly test run. 158. What are the assembly methods for interference fit connectors? Answer: 1) Pressing fitting method: This method can be divided into the hammering method and the press pressing method. 2) Thermal expansion fitting method: This involves using a thermal installation approach. It is commonly used in the assembly of interference fittings with the greatest degree of interference. 3) Cold shrinkage compounding method: This involves using a cold installation approach. It is characterized by a small amount of shrinkage, and is generally used in situations where the interference amount is small but constraints imposed by certain methods apply. 4) Hydraulic sleeve method: A hydraulic approach is used for hole expansion. Interference fit used for shaft retraction assembly. 159. What are the lead and pitch of a thread? What is the relationship between them? Answer: Lead: It is the distance that a point on a thread moves along the axis direction as it completes one full turn along the helical path. Pitch: It is the axial distance between corresponding points of two adjacent teeth. Relationship: The lead of a single-start bolt is equal to the pitch, while the lead of a multi-start thread is equal to the product of the number of starts and the pitch. 160. Why is it necessary to prevent loosening in threaded connections? What are the common methods for loosening a house? Answer: Generally, threaded connections can meet the self-locking conditions and will not come loose on their own, but they may loosen due to vibration and impact loads or significant temperature changes. To ensure reliability of the connection, measures to prevent loosening should be considered during design. Methods: 1) Friction anti-loosening. 2) Mechanical anti-loosening. 3) Other anti-loosening methods. Such as: pins, nails, shims, caps, etc. 161. What are the four principles that should be followed in the handling of equipment accidents? Answer: 1) The cause of the accident will not be left unresolved. 2) The persons responsible for the accident and the public were not spared by the Ministry of Education. 3) No case will be overlooked without preventive measures. 4) Those responsible must not go unpunished. 162. What are the contents of the four understandings and three skills for operators? Answer: 1) Four understandings: understanding the structure of the equipment, understanding its performance, understanding its principles, and understanding its purposes. 2) Three skills: knowing how to use it, knowing how to maintain it, and knowing how to troubleshoot faults. 163. What is the “five-point” inspection method for pumps? Answer: The “five-word” inspection method is listening, touching, testing, observing, and smelling. 164. What is the “cross” maintenance method for chemical process centrifugal pumps? Answer: The “Cross” maintenance method consists of cleaning, organizing, lubricating, tightening, and adjusting.