Working principles and characteristics of various pumps

Thread Content

Pumps are primarily used to transport liquids such as water, oil, acids, alkalis, emulsions, suspensions, and liquid metals. They can also handle mixtures of liquids and gases, as well as liquids containing suspended solids. In this article, we will explore, through animations, the working principles and performance characteristics of various pumps, in the hope of being helpful to everyone (of course, not all of these pumps are used in vacuum applications). I. Gear Pump The teeth of the two gears in a gear pump are separated from each other, creating a low pressure that allows liquid to be drawn in and then pushed to the other side by the shell walls. On the other side, the two gears close together to generate high pressure and force the liquid out. 　　Performance characteristics of gear pumps Advantages of gear pumps: Simple and compact structure, small size, light weight, good manufacturability, low cost, strong self-priming ability, insensitivity to oil contamination, wide speed range, capability to handle shock loads, easy maintenance, and reliable operation. 　　Disadvantages of gear pumps: unbalanced radial forces, large flow fluctuations, high noise levels, low efficiency, poor interchangeability of components, difficulty in repair after wear, and inability to be used as variable displacement pumps. II. Multi-stage centrifugal pumps Multi-stage centrifugal pumps are equivalent to multiple centrifugal pumps connected in series, with pressure being increased stage by stage, thereby enabling the achievement of a higher head pressure. 　　Performance characteristics of multi-stage centrifugal pumps: Compared with single-stage pumps, multi-stage centrifugal pumps have two or more impellers, which allow water to be drawn in and pushed out in stages, thereby lifting the water to a very high height. The head can be increased or decreased by adjusting the number of impeller stages in the pump, according to requirements. Multi-stage pumps are mainly used for mine drainage and water supply in cities and factories; they are rarely used in agricultural irrigation. They are only suitable for lifting water in high mountain areas with high head and low flow rates, in order to address the problem of providing drinking water for humans and animals. Multi-stage high-head pumps are available in both vertical and horizontal types. The pump shaft of a multi-stage centrifugal pump is equipped with two impellers connected in series, which allows it to achieve a higher head compared to ordinary single-stage centrifugal pumps ； Compared to reciprocating pumps such as piston pumps and diaphragm pumps, it can also pump larger flow rates. Multi-stage centrifugal pumps have high efficiency and can meet the requirements of high head and high flow rates; they are widely used in industries such as petrochemicals, chemicals, power generation, construction, and firefighting. 　　Due to its inherent characteristics, compared to single-stage centrifugal pumps, multi-stage centrifugal pumps require different and higher technical standards in terms of design, operation, as well as maintenance and repair. It is often negligence or inadequate consideration of certain details by people that leads to frequent problems such as abnormal wear, vibration, and shaft seizure in multi-stage centrifugal pumps after they are put into use, resulting in shutdowns as well. III. Centrifugal Pumps When a centrifugal pump is in operation, the pump casing is filled with liquid; the impeller rotates at high speed, and the liquid acquires high velocity due to centrifugal force. The high-velocity liquid passes through the progressively widening channels in the pump casing, where the dynamic head is converted into static head. 　　Performance characteristics of centrifugal pumps: 1. High efficiency and energy savings: CFD computational fluid dynamics is used to analyze and determine the pressure and velocity distributions within the pump, thereby optimizing the pump’s flow channel design. This results in an efficient hydraulic geometry for the pump, enhancing its efficiency. 　　2. Easy installation and maintenance: With its vertical pipe-style design, the pump’s inlet and outlet can be installed at any position and in any direction along the pipeline, just like valves, making installation and maintenance extremely convenient. 　　3. Smooth operation, safe and reliable: The motor shaft and the pump shaft are connected in a coaxial manner with a high degree of concentricity, ensuring smooth operation as well as safety and reliability. 　　4. Stainless steel shaft sleeves: The location of the mechanical seal on the shaft is a place prone to rusting; once the shaft of a direct-drive pump gets rusty, it can lead to the failure of the mechanical seal. The STG pump is equipped with stainless steel shaft sleeves here, which prevents rusting, extends the lifespan of the shaft, and reduces operating and maintenance costs. 　　5. Bearings: In the motors used with the pump, the shaft end bearings for models Y〔Y2〕280 and below [including the blade end bearings for models Y180 and below] are of the sealed type; under normal operation, no maintenance is required for these motor bearings. 　　6. Mechanical seal: The mechanical seal components generally employ a rubber bellows structure, replacing the linear sealing provided by O-rings in traditional mechanical seals with a double-face sealing mechanism using rubber elements, which improves the sealing performance in clean water media. IV. Screw Pumps Double-screw pumps are very similar to gear pumps: one screw rotates, driving the other screw; the liquid is trapped within the meshing chamber, pushed in the direction of the shaft, and then forced out toward the center. 　　Performance characteristics of screw pumps Advantages of screw pumps: 1. Wide range of pressure and flow rates. The pressure ranges from about 3.4 to 340 kilogram-force per square centimeter, and the flow rate can reach 100 cm3 per minute ； 　　2. A wide range of liquid types and viscosity levels are available for transportation ； 　　3. Since the inertial force of the rotating components inside the pump is low, a very high rotational speed can be used ； 　　4. Good suction performance, with self-priming capability ； 　　5. Uniform and continuous flow, minimal vibration, low noise ； 　　6. Compared to other rotary pumps, it is less sensitive to the gases and contaminants that enter it ； 　　7. Robust structure, easy to install and maintain. 　　Disadvantages of screw pumps High requirements for the machining and assembly of screws ； The performance of the pump is sensitive to changes in the viscosity of the liquid. V. Bypass regulation of reciprocating pumps Reciprocating pumps are positive-displacement pumps. When the flow rate provided by the pump exceeds the demand of the pipeline, it is necessary to return a portion of it to the inlet of the reciprocating pump, as well as to use a bypass for regulation. VI. Pneumatic diaphragm pump: When in operation, a pneumatic diaphragm pump uses a diaphragm to separate the cylinder chamber from the corrosive liquid, so as to prevent the plunger from coming into direct contact with it; this is essentially based on the principle of a reciprocating pump. 　　Performance characteristics of pneumatic diaphragm pumps Pneumatic diaphragm pumps are a new type of conveying machinery and represent the most innovative pump design available in China at present. Uses compressed air as a power source, suitable for various corrosive liquids. Pneumatic diaphragm pumps are available in four materials: engineering plastics, aluminum alloy, cast iron, and stainless steel. Pneumatic diaphragm pumps use nitrile rubber, neoprene, fluororubber, polytetrafluoroethylene, and polyhexafluoroethylene depending on the different liquid media. To meet the needs of different users. Installed in various special applications to pump fluids that conventional pumps cannot handle, it has achieved satisfactory results. 　　1. The pump will not overheat: Compressed air is used as the driving force, and the exhaust process involves expansion and heat absorption; therefore, the temperature of the pneumatic pump decreases during operation, with no harmful gases being emitted. 　　2. No electric sparks are generated: Pneumatic diaphragm pumps do not rely on electricity for operation, and grounding prevents the occurrence of static sparks. 3. They can handle liquids containing particles: Thanks to their positive displacement mechanism and ball valves at the inlet, they are less likely to get clogged. 　　4. The shear force on the material is extremely low: it draws in and discharges the material in the same way it was taken in, so there is minimal disturbance to the material; this makes it suitable for transporting unstable substances. 5. The flow rate can be adjusted by installing a throttle valve at the material outlet. 　　6. It has a self-priming function. 　　7. It can run without load without any risk. 　　8. Can work as a diver. 　　9. It can transport a very wide range of fluids, from those with low viscosity to those with high viscosity, and from corrosive substances to viscous ones. 　　10. There is no complex control system, no cables, fuses, etc. 　　11. Small in size and light in weight, making it easy to move. 　　12. No lubrication is required, so maintenance is simple, and it does not contaminate the working environment due to leaks. 　　13. The pump always maintains high efficiency and does not see a decrease due to wear. 　　14. 100% energy utilization: the pump stops automatically when the outlet is closed, preventing issues such as equipment movement, wear and tear, overload, and overheating. 15. No moving seals are required, which simplifies maintenance and eliminates the risk of leaks. There is no dead point during operation. VII. Reciprocating Pump When the reciprocating pump is in operation, the piston moves to the right, causing the pressure inside the chamber to decrease. This lowers the upper valve while raising the lower valve, allowing liquid to be drawn in ； The piston moves to the left, increasing the pressure inside the chamber; this pushes the upper valve upward while pressing the lower valve downward, allowing the liquid to be discharged. 　　Performance characteristics of reciprocating pumps Advantages of reciprocating pumps: 1. They can achieve very high discharge pressures; the flow rate is independent of pressure. They have good suction performance and high efficiency, with steam reciprocating pumps achieving efficiencies of 80% to 95% ； 　　2. In principle, it can transport any medium, with little limitation imposed by the physical or chemical properties of the medium ； 　　3. The performance of the pump does not change with variations in pressure or the viscosity of the fluid being transported. 　　Other pumps do not possess the aforementioned advantages of reciprocating pumps, but they have a simpler structure, are easier to operate, and also offer the benefits of small size, light weight, uniform flow rate, as well as the possibility of mass production in series. 　　Disadvantages of reciprocating pumps: The flow rate is not very stable. It is larger than centrifugal pumps at the same flow rate ； Complex structure ； High capital usage ； Difficult to maintain, etc. VIII. Double-acting reciprocating pump: When the double-acting reciprocating pump is in operation, the piston moves to the right; liquid is drawn in from the lower left, and liquid is discharged from the upper right. The piston moves left, drawing liquid from the lower right, and discharging it from the upper left. With each back-and-forth movement of the piston, there are two instances of liquid suction and discharge, resulting in a more uniform flow rate. IX. Water ring vacuum pump – The impeller of a water ring vacuum pump is eccentric with respect to the pump casing; a certain amount of water is filled inside the casing, and as the impeller rotates, this water forms a water ring. As the adjacent blades (the red blades in the figure) rotate, the space formed with the water ring (the air chamber) expands, allowing air to enter; as the air chamber gradually shrinks, the air is compressed. Multiple sets of adjacent blades, that is, multiple sets of reciprocating compression. It features a compact structure, reliable and balanced operation, as well as uniform flow, which makes it commonly used in chemical production for transporting or pumping flammable, explosive, and corrosive gases. Water ring vacuum pumps have very low efficiency because the impeller stirs the liquid, resulting in significant energy loss. 　　Performance characteristics of water ring vacuum pumps Advantages of water ring vacuum pumps 1. Simple structure, low requirements for manufacturing precision, and easy to manufacture. 　　2. It has a compact structure, with a high rotational speed; it can generally be connected directly to the motor without the need for a reduction gear. Therefore, a small structural size can yield a large displacement, while also requiring less floor space. 　　3. Compressed gas is essentially isothermal, meaning that the temperature changes very little during the compression process. 　　4. Since there are no metal-friction surfaces inside the pump chamber, no lubrication is required for the pump, and wear is minimal. The sealing between the rotating part and the fixed part can be achieved directly by a water seal. 　　5. Even air intake, stable and reliable operation, simple to use, and easy to maintain. 　　Disadvantages of water ring vacuum pumps: 1. Low efficiency, generally around 30%, with better models reaching up to 50%. 　　2. The vacuum level is low, not only due to structural constraints but more importantly due to the saturated vapor pressure of the working fluid. Using water as the working fluid, the ultimate pressure can only reach 2000~4000 Pa. Using oil as the working fluid, a pressure of 130 Pa can be achieved. 　　In short, since the gas compression in a water ring pump is isothermal, it is possible to pump out flammable and explosive gases. Due to the absence of exhaust valves and friction surfaces, it is possible to extract dusty gases, condensable gases, and gas-water mixtures. Thanks to these prominent features, it is still widely used despite its low efficiency. 　　Example of community water supply demonstration. X. Vortex pump: The liquid in the grooves of the vortex pump’s blades is flung toward the flow channel by centrifugal force, resulting in pressure increase in one step ； The liquid in the flow channel enters the groove again due to the low pressure created by the liquid being ejected from the groove, thereby generating pressure once more ； The vortex motion of multiple grooves, one flow channel, and one groove enables a higher head pressure to be achieved. 　　Performance characteristics of vortex pumps Advantages of vortex pumps 1. The W-type single-stage directly-connected vortex pump is designed for pumping clean water or liquids with physical and chemical properties similar to water; the operating temperature of the liquid should not exceed 60 degrees Celsius. It is commonly used in boiler feed systems, and finds wide application in various fields such as shipbuilding, light industry and textiles, chemicals, metallurgy, machinery manufacturing, aquaculture, fixed fire protection systems for pressure stabilization, heat exchange units, and agricultural remote irrigation systems. 　　2. The small size and light weight of vortex pumps offer significant advantages in ship applications. It has self-priming capability or can achieve self-priming with the help of a simple device. 　　3. It has a steep head curve, and therefore is insensitive to pressure fluctuations in the system. Certain vortex pumps can achieve the transportation of vapor-liquid mixtures. This is of great significance for pumping volatile liquids containing gases and high-temperature liquids with very high vaporization pressures. 　　4. Vortex pumps have a simple structure, and their casting and machining processes are easy to implement; moreover, certain components of vortex pumps can be made from non-metallic materials such as plastic or nylon molded impellers. 　　Disadvantages of vortex pumps: 1. Their efficiency is relatively low, not exceeding 55% in the best cases; most vortex pumps have an efficiency of 20-40%, which hinders their development towards higher power levels. 　　2. The cavitation performance of the vortex pump is poor. 　　3. Vortex pumps cannot be used to pump media with high viscosity. As the viscosity of the liquid increases, the pump’s head and efficiency drop sharply; therefore, the viscosity of the medium must be kept below 114 centipoise. 　　4. The strict requirements for the radial and axial clearances between the impeller of the vortex pump and the pump body present certain difficulties in the processing and assembly processes. 　　5. The medium to be pumped is limited to pure liquids only. When a liquid contains solid particles, wear causes an increase in the axial and radial clearances, which reduces the pump’s performance or even prevents the vortex pump from functioning. XI. Vane Pumps Historically, vane pumps have been divided into two types depending on their category: 1) Referring specifically to sliding vane pumps among positive displacement pumps. II) Refers to the three types of dynamic pumps (centrifugal pumps, mixed-flow pumps, axial-flow pumps) or other special pumps. Pump products of this type are generally not called vane pumps. However, as a specialized subject, vane pumps almost always refer to centrifugal pumps, mixed-flow pumps, axial flow pumps, etc. (In the 2014 exam material for first-level constructors on \"Mechanical and Electrical Engineering and Management Practice,\" these three types are referred to as impeller pumps). Based on whether their theoretical displacement per revolution is fixed or variable, they can be divided into vane variable pumps and vane fixed-displacement pumps. 　　Performance characteristics of vane pumps Advantages of vane pumps 1. The output flow rate is more uniform compared to gear pumps; operation is smooth with low noise levels. 　　2. The working pressure is high, and the volumetric efficiency is also high. 　　3. Single-acting vane pumps (Tokimec vane pumps) are easy to adjust for flow rate, while double-acting vane pumps have a longer service life due to the radial hydraulic pressure that balances the rotor. 　　4. Compact structure, small footprint with high flow rate. 　　Disadvantages of vane pumps: 1. Their self-priming capability is inferior to that of gear pumps, and they require stricter conditions for oil suction; their rotation speed must be within the range of 500~1500 r/min. 　　2. It is sensitive to oil contamination; the blades can easily be damaged by impurities in the oil, resulting in poor operational reliability. 　　3. The structure is relatively complex, the precision requirements for component manufacturing are high, and the price is high. Vane pumps are generally used in medium-pressure (6.3 MPa) hydraulic systems, mainly for machine tool control. In particular, double-acting vane pumps (Tokyo Kikai SQP vane pumps) are widely used in precision machine tools due to their very low flow rate pulsation. XII. Steam Jet Pump: When a steam jet pump is in operation, steam enters the nozzle and is ejected at high speed, creating a low pressure that draws in gas; these gases are mixed in a mixing chamber, and after passing through an expansion tube, their kinetic energy is converted into pressure energy. If the gas being drawn in comes from a container, and the pressure in that container is reduced, it can be called a jet vacuum pump. 　　Performance characteristics of steam jet pumps: 1. These pumps have no mechanical moving parts, and are not subject to constraints such as friction, lubrication, or vibration; therefore, they can be designed to have a high pumping capacity. As long as the structural materials of the pump are chosen appropriately, it is highly advantageous for removing gases with corrosive properties, gases containing mechanical impurities, as well as water vapor. 　　2. It has a simple structure, is lightweight, and occupies little space. 　　3. The working steam pressure is 4–9×105 Pa, and such a source of steam is available in typical metallurgical, chemical, pharmaceutical, and other types of enterprises. 　　Due to the aforementioned characteristics, steam jet pumps are widely used in industrial sectors such as metallurgy, chemicals, pharmaceuticals, petroleum, and food processing. 13. Axial flow pipeline pump The impeller of an axial flow pipeline pump is designed in an axial flow configuration. The rotation speed is very high; if the motor power, impeller diameter, and pipe diameter are large enough, the flow rate can be high. 　　Performance characteristics of axial flow pipeline pumps: 1. Pipeline pumps have a compact structure; the pump and motor are integrated, resulting in a small size. Their vertical design allows for less space required for installation, stable operation, and no need for adjustments during installation. 2. The pump’s inlet and outlet are equipped with flanges of the same standard and are aligned on the same axis, enabling them to be installed directly on pipelines like valves. Their low center position facilitates pipeline layout and simplifies installation. 3. The pump and motor are coaxial, resulting in a short axial dimension that contributes to smoother operation and lower noise levels. 4. Traditional shaft sealing methods are not used, which prevents leakage of the medium being transported; thus, these pumps feature complete leak-free operation. 14. Self-priming pumps: The working principle of self-priming pumps is that water is first filled inside the pump casing before the pump is started (or the pump casing already contains water). After startup, the high-speed rotation of the impeller causes the water in the impeller channels to flow toward the volute; this creates a vacuum at the inlet, which opens the inlet check valve. Air from the suction pipe enters the pump and moves through the impeller channels to the outer edge. 　　Performance characteristics of self-priming pumps Self-priming pumps are a type of self-priming centrifugal pump. They offer advantages such as a compact structure, easy operation, stable performance, simple maintenance, high efficiency, long service life, and strong self-priming capability. There is no need to install a foot valve in the pipeline; before operation, it is sufficient to ensure that a certain amount of liquid is stored inside the pump. Different liquids can use self-priming pumps made of different materials. 　　1. Strong sewage discharge capacity: A special impeller design that prevents clogging ensures efficient operation of the pump with no blockages. 　　2. High efficiency and energy savings: Thanks to an excellent hydraulic design, its efficiency is 3–5% higher than that of ordinary self-priming pumps. 　　3. Good self-priming performance: The self-priming height is 1 meter higher than that of ordinary self-priming pumps, and the self-priming time is shorter. 15. Piston Pump A piston pump operates by the reciprocating motion of a piston within a cylinder, which causes the volume inside the cylinder to change repeatedly in order to draw in and discharge fluid. 　　Performance characteristics of piston pumps Piston pumps, also known as electric reciprocating pumps, are classified into single-cylinder and multi-cylinder types based on their structure, and they are characterized by a high head pressure. Suitable for transporting oil emulsions and similar substances at room temperature without solid particles. Used in oil fields, coal seam water injection, oil injection, and oil production ； Power pumps for chamber presses and hydraulic presses, hydraulic sand cleaning, transportation of ammonia liquid in fertilizer plants, etc. If the overcurrent component is made of stainless steel, it can transport corrosive liquids. Additionally, depending on the material of the structure, it can also transport high-temperature tar, mine sludge, high-concentration grout, high-viscosity liquids, and more. 　　Piston pumps are suitable for applications requiring high pressure and low flow rates; especially when the flow rate is less than 100 cubic meters per hour and the discharge pressure is greater than 9.8 megapascals, they exhibit high efficiency and excellent operating performance. It has good suction performance and can draw in liquids of various media and viscosities. Therefore, it is widely used in industries such as the petrochemical industry, machinery manufacturing, papermaking, food processing, and pharmaceutical production. Low and medium-speed piston pumps have low speeds; they can be operated by hand or pulled by animals, and are suitable for rural water supply and small-scale irrigation. 16. Roots Vacuum Pumps: The working principle of Roots pumps is similar to that of Roots blowers. Due to the continuous rotation of the rotor, the gas to be pumped is drawn in through the inlet into the space v0 between the rotor and the pump casing, and then discharged through the outlet. Since the v0 volume is completely sealed after inhalation, the gas in the pump chamber does not compress or expand. But when the top of the rotor passes over the edge of the exhaust port and space v0 becomes connected to the exhaust side, the higher gas pressure on the exhaust side causes some gas to flow back into space v0, resulting in a sudden increase in gas pressure. As the rotor continues to rotate, the gas is expelled from the pump. 　　Performance characteristics of Roots vacuum pumps: 1. High pumping speed over a wide pressure range ； 　　2. Fast startup, able to start working immediately ； 　　3. It is not sensitive to dust and water vapor present in the gas being sampled ； 　　4. The rotor does not require lubrication, and there is no oil in the pump chamber ； 　　5. Low vibration, good rotor dynamic balance conditions, no exhaust valve ； 　　6. Low driving power and low mechanical friction losses ； 　　7. Compact structure with small floor area ； 　　8. Low operating and maintenance costs. 　　Therefore, rotary vane pumps are widely used in the metallurgy, petrochemical, papermaking, food, and electronics industries. 17. Rotary vane vacuum pump: The vanes of a rotary vane pump divide the crescent-shaped space enclosed by the rotor, the pump chamber, and the two end caps into three sections: A, B, and C. As the rotor rotates in the direction indicated by the arrow, the volume of section A, which is in communication with the suction port, gradually increases, indicating that suction is taking place. Meanwhile, the volume of space C connected to the exhaust port is gradually decreasing, and it is in the exhaust process. The volume of the centered space B is also gradually decreasing; it is in a state of compression. 　　As the volume of space A gradually increases (i.e., expands), the gas pressure decreases. The external gas pressure at the pump inlet is higher than the pressure inside space A, so the gas is drawn in. When space A is isolated from the intake port, that is, when it moves to the position of space B, the gas begins to be compressed, the volume gradually decreases, and eventually it becomes connected to the exhaust port. When the compressed gas exceeds the exhaust pressure, the exhaust valve is pushed open by the compressed gas, allowing the gas to pass through the oil layer in the tank and be released into the atmosphere. Continuous operation of the pump achieves the purpose of continuous pumping. If the exhaust gas passes through the air duct to another stage (the low vacuum stage), is drawn away by that stage, and then compressed by it before being released into the atmosphere, this constitutes a two-stage pump. At this point, the total compression ratio is handled by two stages, thereby improving the ultimate vacuum level. 　　Performance characteristics of rotary vane vacuum pumps A rotary vane vacuum pump (abbreviated as rotary vane pump) is a oil-sealed mechanical vacuum pump. Its operating pressure range is 101325~1.33×10-2 (Pa), classifying it as a low vacuum pump. It can be used alone or as a pre-pump for other high-vacuum pumps or ultra-high-vacuum pumps. It has been widely applied in production and research sectors such as metallurgy, machinery, military industry, electronics, chemicals, light industry, petroleum, and pharmaceuticals. 　　1. Small size, light weight, low noise ； 　　2. Equipped with a gas trap valve to remove a small amount of water vapor ； It can operate continuously for extended periods at ambient temperatures ranging from 5 degrees Celsius to 40 degrees Celsius, as long as the inlet pressure is below 1.3X103 Pascals; when the relative humidity of the gas being pumped is above 90 percent, the pressure relief valve should be activated. 　　3. Equipped with an automatic anti-backflow check valve, ensuring easy operation ； 　　4. The air inlet must remain unobstructed; continuous operation in atmospheric conditions shall not exceed one minute ； 　　5. It is not suitable for pumping gases that are corrosive to metals, that react chemically with the pump oil, that contain particulate dust, as well as gases with high oxygen content, that are explosive, or that are toxic. 18. Mud Pump A mud pump is a machine that is used to deliver mud or water, and other flushing fluids, into the drill hole during drilling operations. Mud pumps are an important component of drilling equipment. In conventional down-the-hole drilling, a flushing medium from the surface – such as clean water, mud, or polymer-based fluid – is forced under pressure through high-pressure hoses, nozzles, and the central hole in the drill string to reach the bottom of the bit. This serves to cool the bit, remove the cut rock debris, and transport it to the surface. The commonly used mud pumps are piston-type or plunger-type; a power unit drives the pump’s crankshaft to rotate, and the crankshaft, in turn, causes the piston or plunger to move back and forth within the pump cylinder through a crosshead. Through the alternating action of the intake and discharge valves, pumping and circulating the flushing fluid is achieved. 　　Performance characteristics of mud pumps 1. Capable of transporting high-concentration, high-viscosity fluids