reciprocating pump

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The reciprocating pump is one of the earliest developed power machines and it is a positive displacement pump. In production, it is used to transport high-pressure liquids or various liquids with high viscosity, corrosiveness, flammability, explosiveness, and toxicity. Especially when the flow t is small, the advantages of this pump become more obvious. The flow rate is less than 100m'/h and the pressure is higher than 100MPa. 1. The working principle of a reciprocating pump. The reciprocating pump relies on the reciprocating motion of the piston or plunger in the cylinder to change the volume of the working chamber, thereby transporting liquid. It consists of two basic parts: the pump body that transports liquid and the transmission mechanism that transmits the energy of the prime mover to the piston. The pump body consists of a piston, a pump cylinder, a working chamber, a valve and a pipeline transportation system. The transmission mechanism consists of a crank, connecting rod, crosshead, etc., as shown in Figure 1. When the piston moves from the left end to the right end of the pump cylinder, the volume in the pump cylinder on the left side of the piston increases, and at the same time the pressure decreases, and the discharge valve is tightly closed. Under the action of atmospheric pressure, the liquid in the reservoir opens the suction chamber along the suction pipe and enters the pump cylinder until the piston moves to the right end, the pump cylinder is filled with liquid, and the liquid suction process ends. Then, driven by the crank connecting rod, the piston moves from the right dead center to the left. The liquid in the pump cylinder is squeezed, and the pressure gradually increases and opens the discharge valve, causing the liquid to be discharged from the discharge pipe. Until the piston moves to the leftmost end, all the liquid in the pump cylinder is discharged, and the discharge process ends. The piston then sucks, compresses and discharges liquid. The discharge valve is closed during the suction process, and the suction valve is closed during the hydraulic pressure and discharge processes. Working in this way over and over, the liquid is sucked in from the liquid storage tank one by one and sent to the drain pipe and the piping system connected with it. This is how a reciprocating pump works. Figure 1 Working principle of reciprocating pump 1-liquid storage tank ； 2-Suction valve ； 3-Studio ； 4-Discharge valve ； 5-Pump cylinder ； 6-piston ； 7-Cross head ； 8-Connecting rod ； 9-The crank piston moves back and forth once to complete the suction and discharge process once, which is called a working cycle. The distance the piston moves from one end to the other is called the stroke or stroke of the piston, and the left and right end points are called stop points. 2 Classification of reciprocating pumps There are many types of reciprocating pumps, which are generally classified according to the structural characteristics of the fluid end and transmission end. 1. Classification according to the structural characteristics of the liquid end (1) According to the type of pump head, it can be divided into piston (plunger) pump and diaphragm pump. (2) According to the functional characteristics, it can be divided into single-acting pump, double-acting pump and differential pump. The single-acting reciprocating pump has the suction valve and the discharge valve installed on the same side of the piston (plunger). In a working cycle, there is only one suction process and one discharge process, as shown in Figure 2. A double-acting reciprocating pump has a suction valve and a discharge valve installed on both sides of the piston (plunger). In a working cycle, there are two suction processes and a discharge process, as shown in Figure 3. A differential pump has a suction valve and a discharge valve installed on one side of the piston. The discharge pipe of the pump is connected to the other side of the piston (without a suction valve and a discharge valve). In a working cycle, there is one suction process and two discharge processes, as shown in Figure 4. The cross-sectional area of ​​the pump plunger is twice the cross-sectional area of ​​the plunger rod. (3) According to the number of liquid cylinders, they are divided into single-cylinder, double-cylinder and multi-cylinder pumps. 2. Classification based on the structural characteristics of the transmission end (1) Motorized pumps include reciprocating pumps driven by electric motors and internal combustion engines. A motorized pump uses a motor, internal combustion engine, etc. as power to make the piston (plunger) reciprocate through a crank-connecting rod mechanism. The instantaneous flow rate of this pump is pulsating. (2) Direct-acting pumps include steam, gas, and hydraulic directly driven reciprocating pumps. Direct-action pumps use water vapor, compressed air or liquid with a certain pressure to drive the piston (plunger) to reciprocate. Water vapor is the most commonly used. The piston rod of the power cylinder is directly connected to the piston rod of the pump cylinder, and they reciprocate together. The instantaneous flow pulsation of this kind of pump is smaller than that of a motorized pump, and it is reliable in operation and easy to adjust the flow rate. Figure 5 shows the structural diagram of a steam direct action reciprocating pump, which consists of a pump cylinder, a cylinder and a connecting part. The pump cylinder part consists of a pump cylinder, a piston, a suction valve, a discharge valve and a piston rod sealing device. The cylinder is the power part of the pump and consists of a cylinder, a piston and a steam distribution valve. The connection part consists of rocker arm, tie rod and connector. The cylinder piston and the pump cylinder piston are connected together through a connector so that the pump cylinder piston produces the same stroke as the cylinder piston. The steam distribution mechanism and the cylinder piston are connected through tie rods and rocker brackets, so that the steam distribution mechanism can coordinate its movements to ensure that steam can be continuously distributed into the left and right sides of the cylinder, thereby pushing the piston to reciprocate. 3 Main performance characteristics of reciprocating pumps Compared with centrifugal pumps, reciprocating pumps have the following characteristics: (1) The discharge pressure can be infinitely high. Since liquid is incompressible, the pressure generated can be very high. As long as the power of the motor, the strength of the pump itself and the pipe material are sufficient, in theory, the discharge pressure of the reciprocating pump can be infinitely high. Therefore, when the reciprocating pump is working, the discharge valve is not allowed to be closed, and a safety valve must be installed on the discharge pipeline. (2) The flow rate has nothing to do with the discharge pressure. Under any discharge pressure, the flow rate is basically unchanged, because the flow rate is related to the piston diameter, stroke and number of reciprocations. Therefore, the flow rate of the reciprocating pump cannot be adjusted by changing the opening of the discharge valve. Generally, the bypass reflux method is used to adjust the flow rate. The QH curve measured by the experiment is shown in Figure 6-53. The solid line represents the theoretical situation, the flow rate does not change with the pressure, and the dotted line represents the actual situation. Due to leakage, the flow rate decreases slightly with the increase of the discharge pressure. (3) A reciprocating pump with self-priming capability uses the reciprocating motion of the piston to change the cylinder volume to absorb and discharge liquid. The suction port and the discharge port are not connected to each other, so it has self-priming ability. The pump does not need to be primed before starting, so there is no need to install a bottom valve. However, in order to avoid dry grinding of the piston and the pump cylinder, some reciprocating pumps are also equipped with a bottom valve, which allows the suction pipeline and pump cylinder to be filled with liquid. (4) The flow rate is uneven. When the reciprocating pump is working, the liquid is discharged periodically, and the flow rate is uneven. The pump is prone to shock and vibration during operation. 4 Installation and maintenance of steam reciprocating pump 4.1 Installation of cluster steam reciprocating pump The steam reciprocating pump has been assembled at the factory and must not be disassembled. When there is any damage and it is necessary to disassemble and inspect the pump, it should be carried out according to the technical documentation provided with the pump. The basic acceptance, alignment, elevation, and level adjustment of reciprocating pumps are basically similar to those of centrifugal pumps. 4.2 Maintenance of steam reciprocating pump 1. Disassembly of steam reciprocating pump Before disassembling the steam reciprocating pump, the condensed water in the cylinder and the residual liquid in the liquid cylinder should be drained. Pay attention to the following two points when disassembling: (1) When disassembling the piston and piston ring, special tools should be used to prevent the piston ring from being broken. (2) When disassembling the steam distribution valve plate, mark it carefully and make sure there is no mistake. 2. Inspection and assembly adjustment of steam reciprocating pump parts. During the disassembly process of the steam reciprocating pump or after the parts have been disassembled and cleaned, the INS should be inspected and assembled according to the requirements of the pump maintenance manual. If there are no requirements, QS, QB, YC and other steam reciprocating pumps can be inspected, measured and assembled according to the standards of SHS 01014-2004 "Steam Reciprocating Pump Maintenance and Inspection Regulations". Its maintenance mainly includes the following aspects. 1) Inspection and repair of steam reciprocating pump parts (1) Pulling mechanism: The fit of the various parts of the pulling mechanism does not meet the specifications. Excessive wear will cause the pump to move unevenly. Therefore, the fit clearance should be checked during maintenance. ①The center bracket bushing and rocker arm shaft match H9/i9 ； ②The matching between the connecting rod bushing and the steam chamber tie rod joint pin is H7/5 ； ③The matching of connecting rod bushing and long and short arm pin is H7/f6. (2) Steam distribution mechanism: ①During the operation of the flat-plate steam distribution valve pump, the valve plane contact is not tight due to the impurities carried by the steam or the mutual friction between the flat plates. Therefore, the coloring method should be used to check the contact between the valve plate and the valve seat plane during maintenance. If the contact is poor, grind it to make the valve plate and valve seat plane smooth, and the contact area should be no less than 2-3 points per square centimeter. The maximum wear amount of the steam tie rod can refer to the maximum allowable wear amount of the piston rod. The surface and threaded part of the steam distribution tie rod should not be damaged or worn, and the nut should be well connected and not loose. ②The cylindricity tolerance of the piston type steam distribution valve without piston ring type steam distribution piston and the matching cylinder is not greater than 0.05mm, and the maximum wear is not more than 0.05mm. The assembly clearance between the piston and the matching cylinder should be within the range of 0.08-0.15mm. If the wear exceeds the standard, it should be replaced. The cylindrical tolerance value of the piston and cylinder with piston ring-type steam distribution, the assembly clearance between the piston and the cylinder, and the technical requirements for the piston ring are the same as those for the cylinder part. The surfaces of the steam distribution piston and cylinder should be smooth and without cracks, and their wear grooves should be less than 0.2mm. (3) Cylinder: The inner surface of the cylinder should be smooth and free of defects such as cracks, blisters, and grooves. Its inner diameter cylindricity tolerance and cylinder inner diameter increase should meet the technical requirements. (4)Liquid cylinder: The inner surface of the hydraulic cylinder liner should be smooth, without defects such as cracks, blisters, grooves, etc. The limit depth of the wear grooves should not exceed the value specified in the technical requirements. If it exceeds the specified value, the cylinder should be repaired or bored. (5) Piston: ①The surface of the piston should be smooth and free of defects such as cracks, blisters, and scars. The cylindricity should meet the technical requirements. If it exceeds the limit value, it should be repaired or replaced. ② The installation clearance of the cylinder, hydraulic cylinder and piston should meet the technical requirements. ③ The dead center clearance of the piston at both ends in the cylinder should meet the technical requirements. (6) Piston rings: ①The piston ring should have no blisters or pores and should have sufficient elasticity. ②The thickness of the cylinder piston ring should be 0.5-1.00mm less than the piston groove depth, and the thickness of the liquid cylinder piston ring should be 0.5-1.50mm less than the piston groove depth. The mounting positions of the piston rings are staggered by 120 degrees from each other. ③No serious longitudinal grooves are allowed on the surface of the piston ring. Its circumference is in good contact with the cylinder wall, and it is not allowed to be inserted with a 0.05mm feeler gauge. ④The installation clearance of steam and hydraulic cylinder piston rings must meet the technical requirements. (7) Piston rod: ①The maximum wear amount and roundness tolerance value of the piston rod should meet the technical requirements. ②No serious longitudinal grooves are allowed on the surface of the piston rod, and the straightness value must meet the technical requirements. ③After the piston and piston rod are assembled, the tolerance value of the verticality between the piston end face and the piston rod should meet the technical requirements. ④The diameter gap between the piston rod and the packing gland should meet the technical requirements. (8) Valve: ①The contact surfaces between the inlet and outlet valve covers and valve seats should be smooth and tight. Use the coloring method to check that the contact surface should be in an annular shape with no interruptions allowed. ②When the difference between the quality of the valve cover and the original quality exceeds the specified value, it should be replaced. ③The valve cover and valve seat must not have corrosion, pit marks, damage, serious radial grooves, etc. ④The number of spring turns, height and elasticity all meet the technical requirements. ⑤The lifting height of the valve cover should be equal, and the deviation should not be greater than 5%. ⑥The valve stem and valve seat hole are concentric, and the valve stem and valve cover hole match H9/c9 or H9/d9. ⑦The valve seat must be firmly and tightly installed on the pump body. (9)Sealing: Please refer to the "Chapter 5 5.1.4 Installation and Use" section. 2) Assembly and adjustment of steam reciprocating pump (1) Assembly of the assembly First assemble two or several parts together, such as piston and piston rod, inlet and outlet valves, etc. Every installation of a part should be carried out in accordance with the specifications to ensure assembly quality. (2) Assembly of components Assembling parts or assemblies into part of the equipment. When assembling components, the quality of the parts and assemblies should be checked, and the relative positions and relationships between the parts and assemblies should be carefully adjusted to meet specification requirements. Generally, the steam exhaust part and pump valve part are assembled first, and then the piston is installed. (3) General assembly assembles parts, assemblies or components into a complete reciprocating pump. After final assembly, the reciprocating pump must comply with the drawings and relevant technical requirements. When assembling, it should be noted that the opening of the piston ring should be staggered with the steam channel and valve hole. If the piston ring is difficult to insert into the cylinder liner, use a screwdriver to pry the piston ring around or tie it tightly with hemp rope, iron wire, etc. You can also use special tools to enable it to enter smoothly. Do not knock it randomly. After all components are assembled, the final "three-point centering" adjustment is required. That is, first measure the length of the steam distribution plate and the steam channel to determine the size of the steam distribution plate in the center of the steam channel, measure the length of the cylinder piston and the cylinder to determine the size of the cylinder piston in the center of the cylinder, measure the length of the liquid cylinder piston and the liquid cylinder to determine the size of the liquid cylinder piston in the center of the liquid cylinder, and then adjust the swing arm to be vertical downward position, and finally adjust the steam distribution plate to the center of the steam passage one by one according to the center size by adjusting the adjusting nut of the steam distribution tie rod, adjust the length of the cylinder piston rod to adjust the cylinder piston to the center of the cylinder, and adjust the length of the liquid cylinder piston rod to adjust the liquid cylinder piston to the center of the liquid cylinder. (4) Adjustment of the steam reciprocating pump. If the stroke of the steam reciprocating pump is uneven during operation, it needs to be adjusted. The piston stroke can be adjusted by adjusting the steam distribution mechanism and controlling the speed and amount of steam entering the cylinder. In a single-cylinder reciprocating pump, the greater the distance between the stroke adjustment nut and the small rocker arm, the greater the piston stroke. If the piston is compared with the middle position as the base point, if the piston has a long stroke to the left and a short stroke to the right, the steam valve on the right entering the cylinder should be closed faster and the steam valve on the left should be opened faster. The adjustment principle of the double-cylinder reciprocating pump is the same as that of the single-cylinder. The adjustment of the stroke size depends on the size of the gap between the square nut and the protruding valve plate. If the size of the piston stroke is relatively to the left or right of the middle position, it can be corrected by adjusting the length or shortening of the small tie rod. 4.3 Trial operation and troubleshooting of steam reciprocating pump 1. Trial operation of steam reciprocating pump 1) Preparations before trial operation (1) Check installation or maintenance records, confirm that the data is correct, and prepare various record forms for trial operation ； (2) Add cylinder oil to the oil injector. The oil level should be between 1/2 and 2/3 of the oil mark. Fill each oil pipe with oil. Turn the handle of the oil injector a few turns to add oil to the oil injection point. (3) Before starting, the piston must be rotated for at least one reciprocation to ensure free and unimpeded movement. (4) Carefully check whether the sealing conditions of each pipe and packing are in good condition. (5) Open the valve on the suction pipe. (6) Open the valve on the discharge pipe. (7) Open the water drain valve of the cylinder until all the condensed water is drained. 2) Trial operation (1) Start: ①After making sure that there is no obstruction to the piston movement and that the valves on each pipeline are open, first introduce steam into the cylinder to suction the cylinder. ②When warming the cylinder, fully open the exhaust steam valve and open the drain valve. ③After the cylinder is normal, close the drain valve. ④Slowly open the main steam valve until the pump is running, paying attention to the outlet pressure ； Close cylinder drain valve ； Gradually adjust the main steam valve to make the pump outlet flow t meet the process requirements and indicators. ⑤Comprehensively check the reciprocating pump for any abnormalities. (2) Parking: ①Gradually close the main steam valve until it is closed, then close the exhaust steam valve. ②Open the drain valve to drain out the water and residual steam. ③Drain the water in the cylinder using the drain valve. ④Gradually stop the cooling water ⑤ Close the inlet valve of the pump (inlet first, then outlet). If it stops working for a long time, the fluid in the cylinder should be drained and cleaned. 2. Troubleshooting of steam reciprocating pumps Common fault phenomena, causes and treatment methods of steam reciprocating pumps are shown in Table 1. Table 1 Common causes of steam reciprocating pump failures and their solutions No. Fault phenomenon Failure causes and solutions 1 Pump cannot start The steam distribution rocker arm pin falls off and the steam inlet valve core is broken. The valve cannot be opened. The cylinder wear gap is too large. The packing is too tight. The cylinder piston ring is broken. The two rocker arms are in a vertical position at the same time. As a result, the wrong steam valve is closed. The opening of the exhaust valve is small. There is condensed water in the cylinder. Insufficient steam pressure. There is pressure or hard objects in the cylinder. Replace the rocker arm pin. Replace the valve or valve core. Replace the cylinder or piston ring. Properly loosen the packing and gland screw. Replace the piston ring. Adjust the piston rod position. Stagger the stroke. Open the exhaust valve and drain the cylinder. Adjust the process of internal condensation water to increase the steam pressure. Eliminate the pressure or hard objects in the liquid cylinder. 2 The pump suddenly stops. The piston ring is broken and stuck, and the piston rocker arm pin falls off. The steam is interrupted or the pressure is insufficient. Excessive stroke causes the piston to fall into the cylinder. Replace the piston ring. Reinstall the rocker arm pin. Check the steam supply system. Adjust the stroke. 3 Pressure Large force fluctuation, the valve is not closed tightly or has different elasticity. The piston ring is not flexible in the groove. The piston is damaged. The inlet pressure is unstable. The medium vaporizes and grinds the valve or replaces the spring. Adjust the fit between the piston ring and the groove. Replace the piston and make process adjustments. Make process adjustments. 4. Insufficient flow. One-way valve is worn. The piston runs too slowly or the stroke The cylinder piston ring is too short and the wear exceeds the standard. The inlet temperature is too high, resulting in vaporization. The liquid level is too low. The opening of the inlet pipe valve of the inhaled gas is small or blocked. Grind or replace. Adjust the number of piston operations and stroke length. Replace the cylinder liner or piston ring. Lower the inlet temperature to ensure a certain liquid level. Increase the opening or clear the pipeline. 5. Material seal leaks, piston rod is severely worn, packing is damaged, insufficient packing, packing gland is too loose, packing gland end face is not parallel to stuffing box end face, replace piston rod, replace packing, interface is staggered, add packing, tighten gland screws evenly and symmetrically, tighten gland screws evenly and symmetrically, tighten packing gland 6, piston rod overheated, lubricator not on oil pan The root is too tight and the oil filling hole is clogged. The piston rod is bent. Repair or replace it. Loosen the packing gland bolts evenly. Clean and straighten or replace them. 7 Abnormal noise and vibration increase. Foreign matter enters the cylinder. The piston stroke is too large or the speed is too fast. The piston lock nut or piston rod lock nut is loose. The cylinder liner is loose. The crosshead center frame is loose. The connection is loose, the anchor bolts are loose, the stroke is uneven, the cylinder condensate is not discharged, the vaporization is evacuated, the foreign matter in the cylinder is removed, the foreign matter in the cylinder is reduced, the stroke length is reduced or the steam intake is adjusted, the lock nut is tightened, the cylinder liner jackscrew is tightened or the cylinder liner is tightened, the anchor bolts are tightened, the stroke is adjusted, the stroke is drained, the cylinder condensate liquid is drained, and the process is adjusted.