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What is a gear pump

What is a gear pump?

Gear pump is a rotary pump that transports liquid or pressurizes it by relying on the change and movement of working volume formed between pump cylinder and meshing gear. Two enclosed spaces are composed of two gears, the pump body and the front and rear covers. When the gear rotates, the volume of the space on the disengaged side of the gear increases from small to large, forming a vacuum, sucking the liquid, the volume of the space on the meshing side of the gear changes from large to small, and squeezing the liquid into the pipeline. The suction chamber and the discharge chamber are separated by the meshing lines of the two gears. The pressure at the outlet of the gear pump completely depends on the resistance at the pump outlet.

20210817084501 75430 - What is a gear pump

Basic concept of gear pump

The concept of gear pump is very simple. Its most basic form is that two gears with the same size mesh and rotate with each other in a closely matched shell. The interior of the shell is similar to an “8” shape. The two gears are installed inside, and the outer diameter and both sides of the gear are closely matched with the shell. The material from the extruder enters the middle of the two gears at the suction port and fills this space. It moves along the shell with the rotation of the teeth and is finally discharged when the two teeth mesh.
In terms, the gear pump is also called positive displacement device, that is, like a piston in a cylinder barrel, when one tooth enters the fluid space of another tooth, because the liquid is incompressible, the liquid and the tooth cannot occupy the same space at the same time. In this way, the liquid will be mechanically squeezed out. Due to the continuous meshing of the teeth, this phenomenon occurs continuously, which provides a continuous discharge at the outlet of the pump. The discharge is the same for each revolution of the pump. With the continuous rotation of the drive shaft, the pump discharges fluid continuously. The flow of the pump is directly related to the speed of the pump.
In fact, there is a small amount of fluid loss in the pump, because these fluids are used to lubricate both sides of the bearing and gear, and the pump body can never fit without clearance, so the fluid can not be discharged 100% from the outlet, so a small amount of fluid loss is inevitable, which makes the operation efficiency of the pump can not reach 100%. However, the pump can still operate well, and the efficiency can still reach 93% ~ 98% for most extruded materials.
For fluids with varying viscosity or density in the process, the pump will not be affected much. If there is a damper, such as a screen or a limiter on the discharge side, the pump will push fluid through them. If the damper changes during operation, that is, if the filter screen becomes dirty, blocked, or the back pressure of the limiter increases, the pump will still maintain a constant flow until the mechanical limit of the weakest component in the device is reached (usually equipped with a torque limiter).
The speed of a pump is actually limited, which mainly depends on the process fluid. If oil is transmitted, the pump can rotate at a very high speed, but when the fluid is a high viscosity polymer melt, this limit will be greatly increased.
It is very important to push the high viscous fluid into the two tooth space on one side of the suction port. If this space is not filled, the pump cannot discharge the accurate flow, so the PV value (pressure × Flow rate) is another limiting factor and a process variable. Due to these limitations, gear pump manufacturers will provide a range of products, namely different specifications and displacement (the amount discharged per revolution). These pumps will be matched with the specific application process to optimize the system capacity and price.
The gear and shaft of PEP-II pump are integrated, and the whole body hardening process can obtain longer service life“ The “d” bearing combines the forced lubrication mechanism to make the polymer pass through the bearing surface and return to the inlet side of the pump to ensure the effective lubrication of the rotating shaft. This property reduces the possibility of polymer retention and degradation. The precision machined pump body can accurately match the “d” bearing with the gear shaft to ensure that the gear shaft is not eccentric to prevent gear wear. Parkool sealing structure and Teflon lip seal together form a water-cooled seal. This seal does not actually contact the surface of the shaft. Its sealing principle is to cool the polymer to a semi molten state to form a self sealing. Rheoseal seal can also be used, which is processed with reverse spiral groove on the inner surface of shaft seal, so that the polymer can be back pressed back to the inlet. In order to facilitate installation, the manufacturer has designed a ring bolt mounting surface to match with the flange installation of other equipment, which makes the manufacturing of cylindrical flange easier.
PEP-II gear pump is equipped with heating elements matching the specifications of the pump, which can be selected by users, which can ensure rapid heating and heat control. Different from the heating mode in the pump body, the damage of these elements is limited to one board and has nothing to do with the whole pump.

Driving device of gear pump

The gear pump is driven by an independent motor, which can effectively block the upstream pressure pulsation and flow fluctuation. The pressure pulsation at the outlet of the gear pump can be controlled within 1%. Using a gear pump in the extrusion production line can improve the flow output speed and reduce the shear and residence time of materials in the extruder.
External gear pump is the most widely used gear pump. General gear pump usually refers to external gear pump. It is mainly composed of driving gear, driven gear, pump body, pump cover and safety valve. The sealing space composed of pump body, pump cover and gear is the working room of gear pump. The axles of the two gears are respectively installed in the bearing holes on the two pump covers. The driving gear shaft extends out of the pump body and rotates driven by the motor. The external meshing gear pump has the advantages of simple structure, light weight, low cost, reliable operation and wide application range.
When the gear pump works, the driving wheel rotates with the motor and drives the driven wheel to rotate with it. When the meshing teeth on one side of the suction chamber are gradually separated, the volume of the suction chamber increases and the pressure decreases, and the liquid in the suction pipe is sucked into the pump; The suction liquid is divided into two paths and pushed to the discharge chamber by the gear in the tooth groove. After the liquid enters the discharge chamber, due to the continuous meshing of the teeth of the two gears, the liquid is squeezed from the discharge chamber into the discharge pipe. The driving gear and driven gear rotate continuously, and the pump can continuously suck in and discharge liquid.
The pump body is equipped with a safety valve. When the discharge pressure exceeds the specified pressure, the delivered liquid can automatically open the safety valve to return the high-pressure liquid to the suction pipe.
The utility model relates to an internal meshing gear pump, which is composed of a pair of mutually meshing internal gears, crescent shaped parts in their middle, a pump shell, etc. The function of the crescent piece is to separate the suction chamber from the discharge chamber. When the driving gear rotates, a local vacuum is formed at the place where the gear disengages from meshing. The liquid is sucked into the pump and filled between the teeth of the suction chamber, and then enters the discharge chamber in two ways along the inner and outer sides of the crescent shaped part. Where the gear teeth enter the mesh, the liquid existing between the teeth is squeezed and sent to the discharge pipe.
In addition to the characteristics of self-priming capacity and flow independent of discharge pressure, the gear pump has no suction valve and discharge valve on the pump shell. It has the characteristics of simple structure, uniform flow and reliable operation, but it has low efficiency, high noise and vibration and is easy to wear. It is mainly used to transport various oils without corrosivity, solid particles and lubrication capacity. The temperature generally does not exceed 70 ℃, For example, lubricating oil, edible vegetable oil, etc. The general flow range is 0.045 ~ 30ms/h, the pressure range is 0.7-20mpa, and the working speed is 1200-4000r/min.
Structural characteristics of gear pump:

  • (1) Simple structure and low price;
  • (2) Low work requirements and wide application;
  • (3) The end cover and each inter tooth groove of the gear form many fixed sealing working cavities, which can only be used as a quantitative pump.

The gear adopts a new international advanced technology in the 1990s – double arc sinusoidal tooth profile arc. Compared with involute gear, its most prominent advantage is that there is no relative sliding on the tooth profile during gear meshing, so the tooth surface has no wear, balanced operation, no liquid trapping, low noise, long service life and high efficiency. The pump gets rid of the shackles of traditional design, which makes the gear pump enter a new field in design, production and use.
The pump is equipped with differential pressure safety valve as overload protection, and the total return pressure of the safety valve is 1.5 times the rated discharge pressure of the pump. It can also be adjusted according to actual needs within the allowable discharge pressure range. However, this safety valve cannot be used as a pressure reducing valve for a long time, and the pressure reducing valve can be installed separately when necessary.
The shaft end seal of the pump is designed in two forms, one is mechanical seal and the other is packing seal, which can be determined according to specific use conditions and user requirements.

Classification of pumps

As for the core component gear, it is mainly composed of common normal gear pump and circular arc gear pump. The public normal gear pump is more durable than the circular arc gear pump in conveying the medium containing impurities. The circular arc gear pump has special structure, conveying clean medium, low noise and long service life.

Working characteristics of gear pump

Advantages: simple and compact structure, small volume, light weight, good manufacturability, low price, strong self suction, insensitive to oil pollution, large speed range, impact load resistance, convenient maintenance and reliable operation.
Disadvantages: unbalanced radial force, large flow pulsation, high noise, low efficiency, poor interchangeability of parts, difficult to repair after wear, and can not be used as variable displacement pump.

Oil trapping phenomenon

Cause: during the operation of the involute gear pump, because the closed volume at the intersection of the gears changes with time, a part of the hydraulic oil is often sealed between the teeth, which is called oil trapping phenomenon. Because the hydraulic oil is incompressible, the external gears will produce great vibration and noise, affecting the normal operation of the system.
Measures: open unloading slots on the front and rear cover plates or floating shaft sleeves. The principle of opening unloading slots: the spacing between the two slots is the minimum closed volume, so that the closed volume is connected with the oil pressure chamber when it changes from large to large, and with the oil suction chamber when it changes from small to large.

Leakage phenomenon

The leakage of the gear pump is large. There are three leakage paths during the operation of the external meshing gear: the first is the gear top clearance, the second is the clearance measurement, and the third is the meshing clearance.
The end clearance leakage is large, accounting for 80% – 85% of the total leakage. When the pressure increases, the former will not change, but the deflection of the latter increases greatly, which is the main reason for the leakage of external gear pump. The volumetric efficiency is low, so it is not suitable for high-pressure pump.
Solution: static pressure balance measures are adopted for end clearance compensation, and a compensation part is added between the gear and the cover plate, such as floating shaft sleeve and floating side plate.

Unbalanced stress

The right side is the oil pressure chamber, the left side is the oil suction chamber, and the pressure of the two chambers is unbalanced; In addition, the pressure of the oil pressure chamber decreases due to the leakage of the tooth top. The two unbalanced pressures act on the gear and shaft, which is called radial unbalanced pressure. The higher the oil pressure, the greater the force, accelerate the bearing wear, reduce the bearing life, bend the shaft, and increase the wear of tooth top and shaft hole.
Preventive measures: use pressure balance groove or reduce oil pressure chamber.

Sealing form of gear pump

  • Mechanical seal;
  • Three layer seal with oil chamber;
  • Single layer seal;
  • Each sealing form of magnetic seal needs to be determined according to different inlet pressure and sealing performance.

Operation and maintenance of gear pump


  • (1) Check the tightness of all pipeline flanges and joints before startup.
  • (2) Turn the coupling without friction and collision sound.
  • (3) The pump shall be filled with delivery liquid during the first start-up.
  • (4) Before startup, the valves in the suction and discharge pipelines shall be fully opened, and it is strictly prohibited to close the valve for startup.
  • (5) After verifying the rotation direction of the motor, start the motor.


  • (1) Turn off the motor.
  • (2) Close the inlet and outlet valves of the pump.

Common faults of gear pump

(1) Fault phenomenon: the pump cannot discharge
Fault cause: a. the rotation direction is opposite; b. The suction or discharge valve is closed; c. There is no material at the inlet or the pressure is too low; d. The viscosity is too high for the pump to bite
Countermeasures: A. confirm the rotation direction; b. Confirm whether the valve is closed; c. Check valves and pressure gauges; d. Check the liquid viscosity and check whether the flow proportional to the speed occurs when running at low speed. If there is flow, the inflow is insufficient
(2) Fault phenomenon: insufficient pump flow
Fault cause: a. the suction or discharge valve is closed; b. Low inlet pressure; c. The outlet pipeline is blocked; d. Stuffing box leakage; e. The speed is too low
Countermeasures: A. confirm whether the valve is closed; b. Check whether the valve is open; c. Confirm whether the discharge is normal; d. Fastening; When a large amount of leakage affects production, stop operation and disassemble for inspection; e. Check the actual speed of the pump shaft
(3) Fault phenomenon: abnormal sound
Fault cause: A. large coupling eccentricity or poor lubrication B. motor fault; c. Abnormal reducer; d. Poor installation of shaft seal; e. Shaft deformation or wear
Countermeasures: A. align or fill lubricating grease; b. Check the motor; c. Check bearings and gears; d. Check the shaft seal; e. Shutdown disassembly inspection
(4) Fault phenomenon: excessive current
Fault cause: a. the outlet pressure is too high; b. Excessive melt viscosity; c. Poor assembly of shaft seal; d. Shaft or bearing wear; e. Motor fault
Countermeasures: A. check downstream equipment and pipelines; b. Check viscosity; c. Check the shaft seal and adjust it properly; d. Check whether the turning gear is too heavy by hand after parking; e. Check the motor
(5) Fault phenomenon: the pump stops suddenly
Fault cause: A. power failure; b. Motor overload protection; c. Coupling damage; d. The outlet pressure is too high, and the interlock reaction; e. Abnormal biting in the pump; f. The shaft and bearing are stuck
Countermeasures: A. check the power supply; b. Check the motor; c. Open the safety cover and conduct turning inspection; d. Check the instrument interlocking system; e. After parking, confirm the positive and negative turntable car; f. Turning confirmation
(6) Fault phenomenon: seal oil leakage
Causes: a. the shaft seal is not properly adjusted; b. The seal ring is worn and the clearance is large; c. The friction surfaces of dynamic and static rings of mechanical seal are damaged with time; d. Spring relaxation
Countermeasures: A. readjust; b. Properly tighten the gland bolts or replace the sealing ring; c. Replace the moving and stationary rings or regrind them; d. Replace the spring

Other phenomena

1. Cause

  • ① The tooth side clearance of inner and outer rotors is too large, so that the pressure suction oil chamber is interconnected, the volumetric efficiency is significantly reduced, and the output flow is not enough;
  • ② Axial clearance is too large;
  • ③ The joint surface in the oil suction pipeline is not tightly sealed, so that the pump sucks in air and the effective suction flow is reduced;
  • ④ Poor oil absorption. For example, the suction flow is reduced due to excessive oil viscosity and the oil filter is blocked by dirt;
  • ⑤ The overflow valve is stuck at the half opening position, and part of the flow from the pump returns to the oil tank through the overflow valve, resulting in insufficient flow into the system. At this time, there is a fault that the system pressure does not go up.

2. Exclusion method

  • ① Replace the inner and outer rotors to make the backlash within the specified range (generally less than 0.07mm);
  • ② Grind the two end faces of the pump body to ensure that the axial clearance of the inner and outer rotors is within 0.02 ~ 0.05mm after assembly;
  • ③ Replace the damaged oil suction pipe seal, wrap the threaded part of the pipe joint with Teflon tape, and then tighten the pipe joint;
  • ④ Select the oil with proper viscosity and clean the oil inlet filter to ensure smooth oil absorption. And increase the oil suction pipe diameter as appropriate;
  • ⑤ Repair the overflow valve and eliminate the phenomenon that the overflow valve is partially shorted to the oil tank, resulting in the reduction of the effective flow of the pump.

Oil trapping phenomenon

For the gear pump to work smoothly, the coincidence degree of gear meshing must be greater than 1, so there are always two pairs of gears meshing at the same time, and some oil is trapped between the closed cavities surrounded by two pairs of gear teeth. The closed cavity gradually decreases with the rotation of the gear, and then gradually increases. The reduction of the volume of the closed cavity will squeeze the trapped oil and produce high pressure, and squeeze it out from the gap, resulting in oil heating and additional load on the parts; The increase of the volume of the closed chamber causes local vacuum, which separates the dissolved gas in the oil and produces cavitation. These will produce strong vibration and noise, which is the oil trapping phenomenon of gear pump.
When the radial unbalance force is large, it can bend the shaft, contact the tooth top with the shell, accelerate the wear of the bearing and reduce the service life of the bearing.
Elimination method
The method to eliminate trapped oil is usually to open unloading slots on the cover plates on both sides, so that when the volume of the closed cavity decreases, it is connected with the oil pressure cavity through the unloading slot on the left, and when the volume increases, it is connected with the oil suction cavity through the unloading slot on the right.

Improve the performance of gear pump

A feasible circuit for improving the performance of gear oil pump
Due to the structural limitation of constant displacement, it is generally considered that the gear pump can only be used as a constant flow hydraulic source.
By directly installing the control valve on the pump, the pipeline between the pump and the directional valve can be omitted, so as to control the cost. Fewer pipe fittings and connectors can reduce leakage and improve working reliability. Moreover, the valve installed on the pump itself can reduce the circulating pressure of the circuit and improve its working performance. The following are some circuits that can improve the basic functions of gear pump, some of which are proved feasible by practice, and some are innovative research.
Unloading circuit
The unloading element will combine the high flow pump with the low-power single pump. Due to the structural limitation of constant displacement, it is generally considered that the gear pump can only be used as a constant flow hydraulic source. Due to the structural limitation of constant displacement, it is generally considered that the gear pump can only be used as a constant flow hydraulic source. However, the scheme of accessory and threaded combined valve is effective for improving its function, reducing system cost and improving system reliability. Therefore, the performance of gear oil pump can be close to that of expensive and complex plunger pump. At this time, the large flow pump circulates the flow from its outlet to the inlet, thus reducing the output flow of the pump to the system, that is, the power of the pump is reduced to a value slightly higher than the required value for the operation of the high-pressure part. The percentage of flow reduction depends on the ratio of unloaded displacement to total displacement at this time. The combined or threaded unloading valve reduces or even eliminates the leakage of pipelines, holes, accessories and other possible leakage.
The simplest unloading element is manually operated. The spring turns on or off the unloading valve. When an operation signal is given to the valve, the on-off state of the valve is switched. Lever or other mechanical mechanism is the simplest way to operate this valve.
Pilot operated (pneumatic or hydraulic) unloading valves are an improvement in the mode of operation because they can be controlled remotely. Its biggest development is the solenoid valve controlled by electrical or electronic switch. It can be controlled not only remotely, but also automatically by microcomputer. It is generally considered that this simple unloading technology is the best case for application.
Manually operated unloading elements are often used in circuits that require large flow for rapid action, large flow for rapid action and reduced flow for accurate control, such as fast telescopic jib circuit. When the unloading valve of the circuit has no control signal, the circuit always outputs large flow. For normally open valves, the circuit will output small flow under normal conditions.
Pressure sensing unloading valve is the most common scheme. Spring action puts the unloading valve in its high flow position. When the circuit pressure reaches the preset value of the overflow valve, the overflow valve opens and the unloading valve switches to its small flow position under the action of hydraulic pressure and pressure. Pressure sensing unloading circuit is mostly used for hydraulic cylinder with high pressure and low speed at the end of stroke. The pressure sensing unloading valve base is basically an automatic unloading element that can be unloaded when the system pressure is reached. It is widely used in odometer splitters and hydraulic vises.
The unloading valve in the flow sensing unloading circuit is also pressed to the high flow position by the spring. The size of the fixed orifice in the valve is determined according to the flow required for the optimal engine speed of the equipment. If the engine speed exceeds this optimum range, the orifice pressure drop will increase, shifting the dump valve to the low flow position. Therefore, the adjacent components of the large flow pump are made into a size that can throttle the maximum flow, so the circuit has the advantages of less energy consumption, stable operation and low cost. Typical applications of this circuit are to limit the circuit flow to the optimal range to improve the performance of the whole system, or to limit the circuit pressure during high-speed driving of the machine. Commonly used in garbage trucks, etc.
The unloading valve of the pressure flow sensing unloading circuit is also pressed by the spring to the large flow position. It will unload no matter whether it reaches the predetermined pressure or flow. The equipment can complete high-voltage operation under idling or normal working speed. This feature reduces unnecessary flow and therefore reduces the required power. Because this circuit has a wide range of load and speed variation, it is often used in excavation equipment.
The pressure sensing unloading circuit with power integration is composed of two groups of slightly changed pressure sensing unloading pumps. The two groups of pumps are driven by the same prime mover, and each pump receives the pilot unloading signal of the other unloading pump. This sensing method is called interactive sensing, which can make one group of pumps work under high pressure and the other group of pumps work under large flow. The two overflow valves can be adjusted according to the special pressure of each circuit to unload one or two pumps. This scheme reduces the power demand, so a low-cost prime mover with small capacity can be used.
Load sensing unloading circuit. When there is no load sensing signal in the control chamber (lower chamber) of the main control valve, all the flow of the pump is discharged back to the oil tank through valve 1 and valve 2; When the load sensing signal is applied to the control valve, the pump supplies liquid to the circuit; When the output pressure of the pump exceeds the predetermined value of the pressure of the load sensing valve, the pump only provides working flow to the circuit, and the excess flow is bypassed back to the tank through the throttling position of valve 2.
Compared with the piston pump, the gear oil pump with load sensing element has the advantages of low cost, strong anti pollution ability and low maintenance requirements.
Priority flow control
Regardless of the speed, working pressure of the gear oil pump or the flow required by the branch, the fixed primary flow control valve can always ensure the flow required for the operation of the equipment. In this circuit, the output flow of the pump must be greater than or equal to the flow required by the primary oil circuit, and the secondary flow can be used for other purposes or return to the oil tank. The fixed primary flow valve (proportional valve) combines the primary control with the hydraulic pump, eliminates the pipeline and eliminates external leakage, so the cost is reduced. The typical application of this gear pump circuit is the steering mechanism often seen on truck cranes, which eliminates a pump.
The function of load sensing flow control valve is very similar to that of fixed value primary flow control: that is, primary flow is provided regardless of pump speed, working pressure or branch pumping demand flow. However, only the required flow is provided to the primary oil circuit through the primary oil port until its maximum adjustment value. This circuit can replace the standard primary flow control circuit to obtain the maximum output flow. Because the pressure of the no-load circuit is lower than the fixed value, the primary flow control scheme has low circuit temperature rise and low no-load power consumption. The load sensing proportional flow control valve is the same as the primary flow control valve. Its typical application is power steering mechanism.
Bypass flow control
For bypass flow control, regardless of the pump speed or working pressure, the pump always supplies liquid to the system according to the predetermined maximum value, and the excess part is discharged back to the oil tank or the inlet of the pump. This scheme limits the flow into the system and makes it have the best performance. The utility model has the advantages that the maximum adjustment flow is controlled through the loop scale and the cost is reduced; The pump and valve are integrated, and the circuit pressure is minimized through the bypass control of the pump, so as to reduce the pipeline and its leakage.
The bypass flow control valve can be designed with a medium ball load sensing control valve that limits the working flow (working speed) range. This type of gear pump circuit is often used in garbage truck or power steering pump circuit that limits hydraulic control to make the engine reach the best speed, and can also be used in fixed mechanical equipment.
Dry oil suction valve
Dry type oil suction valve is a kind of pneumatic hydraulic valve, which is used for pump oil inlet throttling. When the hydraulic pressure of the equipment is unloaded, only a very small flow (< 18.9t/min) passes through the pump; When there is load, the full flow suction pump. This circuit can eliminate the clutch between the pump and the prime mover, so as to reduce the cost and reduce the no-load power consumption. Because the small flow through the circuit maintains the prime mover power of the equipment. In addition, the noise of the pump at no-load is reduced. The dry suction valve circuit can be used for on-off hydraulic systems in any vehicle driven by internal combustion engines, such as garbage loading trucks and industrial equipment.
Selection of hydraulic pump scheme
The working pressure of the gear pump is close to that of the plunger pump. The combined load sensing scheme provides the possibility of variable for the gear pump, which means that the original clear boundary between the gear pump and the plunger pump is becoming more and more blurred.
One of the decisive factors for the rational selection of hydraulic pump scheme is the cost of the whole system. Compared with expensive plunger pump, gear pump has become a practical scheme for many applications because of its low cost, simple circuit and low filtration requirements.

What should be avoided when using gear pump?

The gear pump is applicable to various industries and has a wide range of media. The gear pump has the advantages of firm structure, convenient installation, easy disassembly, simple maintenance, uniform and continuous flow, slight wear, long service life and so on.

  • 1. In the process of using the gear pump, grease should be added frequently. The grease is easy to volatilize, so attention must be paid to adding and changing. Secondly, keep the bearing clean;
  • 2. Put the electric oil well pump in a dry, non corrosive and clean environment after use or use;
  • 3. The gear pump shall be checked and maintained frequently during use. Attention shall be paid to checking the electric oil drum and checking the power line inside; Whether the internal wire, plug and switch can still be used normally; Whether the parts of the bearing are damaged, etc;
  • 4. Each part of the gear pump shall be preserved. During the disassembly and inspection of the gear pump, each part shall be preserved and kept clean.

Maintenance method of gear pump

1. Maintenance of gear pump shaft after wear
The wear of the shaft in the gear pump is mainly due to the friction and wear between the two ends of the shaft and the supporting needle, which makes the shaft diameter smaller. In case of slight wear, the diameter of the shaft at this position can be increased by plating a layer of hard chromium to repair the shaft. If the shaft is seriously worn, it shall be remanufactured with 45 steel or 40Cr steel. After rough and finish turning, the bearing part shall be heat treated with a hardness of hrc60-65, and then ground to make the surface roughness Ra of the bearing mating part not greater than 0.32 μ m; The allowable deviation of roundness and cylindricity of the shaft is 0.005mm; The matching part with the gear shall be H7/H6, and the surface roughness Ra shall not be greater than 0.63 μm.
2. Maintenance of gear pump body after wear
The surface wear of the pump body is mainly the circular arc working surface of the oil suction section. If there is slight wear, it can be used after grinding and deburring with an oilstone. The pump body is formed by cast iron blank. In case of serious wear, it shall be replaced with a new one. If both ends of the gear in the pump are repaired by grinding, the width of the pump body shall also be changed, which is equal to the size removed by grinding at both ends of the gear. The two end faces of the pump body after re machining shall meet the technical requirements.
3. Maintenance after the covers at both ends of the gear pump are worn
The end cover of the gear pump is made of cast iron. In case of wear, it can be ground and leveled on the flat plate. In case of serious wear, it should be ground and leveled on the surface grinder. The plane contact between the polished end cover and the pump body shall not be less than 85%. The flatness tolerance, the perpendicularity tolerance of the end face to the hole center line, the parallelism tolerance of both ends and the parallelism tolerance of the center lines of the two shaft holes are all 0.01mm. The surface roughness Ra after grinding shall not be greater than 1.5 μm.
4. Maintenance and replacement of needle roller bearing for gear pump
After the parts in the pump are repaired, the bearing needle should be replaced. The requirements for needle roller are: the dimensional error of all needle roller diameters shall not exceed 0.003mm, the length tolerance shall be 0.1mm, and the fit clearance with the shaft shall be about 0.01mm; During the assembly of needle rollers, the bearing shell shall be filled according to the quantity requirements, and the needle rollers shall be arranged in parallel with each other.

Maintenance steps of gear pump

Make sufficient preparations before disassembly, and be familiar with equipment structure, process flow and operation status; Care shall be taken during disassembly to avoid damage to equipment parts.
Review data
The fitting clearance of all parts of the gear pump shall be comprehensively checked.
Conduct detailed inspection on the removed parts and components, conduct coloring inspection on the gear, and no cracks are allowed; The taper of the journal is qualified, and the surface shall be free of scratches. The maximum allowable roughness Ra is 1.6 μm; The end cover, bracket and pump body shall be free of obvious defects.
Repair or replace
The parts exceeding the standard shall be replaced, and the parts to be repaired shall meet the standard after repair.
Assembly and adjustment
The axial clearance between gear end face, end cover and bracket is adjusted by changing the thickness of sealing gasket between end cover, bracket and pump body; When tightening the end cover bolts, the force shall be symmetrical and uniform, and the rotor shall be turned while tightening. When the rotor cannot rotate, the bolts shall be loosened and tightened again; When adding packing or installing oil seal, it is still necessary to turn the rotor while tightening the gland, and it shall not be too tight.
Test run
The hydrostatic test shall be 1.5 times of the working pressure and kept free of leakage for 5min. During commissioning, it is qualified if there is no leakage, the operation sound is normal and there is no abnormal vibration, and the outlet pressure meets the requirements.
Repair common sense
With the improvement of repair knowledge of gear pump and application time, gear pump will show problems such as lack of pump oil or even no oil. The main reason is that the relevant parts are worn too much. The wear parts of gear pump mainly include automatic shaft and bushing, intermediate hole and shaft pin of passive gear, inner cavity of pump shell and gear, gear end face and pump cover, etc. After the smooth oil pump is worn, if its primary skill goal fails to meet the requirements, it shall be disassembled and differentiated, the wear position and level shall be found out, and the response method shall be accepted for repair.

  • 1. Repair after the automatic shaft and bushing are worn. After the automatic shaft and bushing of gear pump are worn, their common clearance will increase, which will affect the oil volume of the pump. The normal common clearance can be restored by repairing the automatic shaft or bushing. If the automatic shaft is slightly worn, just press out the old bushing and replace it with a bushing of standard size, and the common clearance can be restored to the allowable limit. If the automatic shaft and bushing are severely worn and the common clearance exceeds the standard, it is not only necessary to change the bushing, but also increase the diameter of the automatic shaft by chromium plating or vibration surfacing, and then grind it to the specified size to restore the common requirements with the bushing.
  • 2. Repair of smooth oil pump shell and repair of shell crack: the shell crack can be repaired by casting 508 nickel brazing electrode. The weld must be tight and free of air holes, and the flatness error of the interface with the pump cover shall not be greater than 0.05mm. Repair of wear of automatic shaft bushing hole and driven shaft hole: after the automatic shaft bushing hole is worn, the wear trace can be eliminated by reaming, and then the bushing increased to the response size can be used. The wear of the driven shaft hole shall also be eliminated by reaming method, and then the repair of the inner cavity of the driven shaft pump shell shall be prepared according to the practical size of the reamed hole: after the inner cavity of the pump shell is worn, it shall be repaired by the inner cavity inlay method, and the inner cavity of the single machine dust collector shall be lined up and then inlaid with cast iron or steel bushing. After inserting the sleeve, the inner cavity shall be lined to the required size, and the bushing protruding from the end face shall be ground off to make it flush with the connecting surface of the pump housing. Repair of valve seat: there are two kinds of pressure limiting valves: ball valve and plunger valve. After the ball valve seat is worn, a steel ball can be placed on the valve seat, and then the steel ball can be knocked quietly with a metal rod until the ball valve is close to the valve seat. If the valve seat is severely worn, ream it first to remove the wear marks, and then use the above method to make it close. After the plunger valve seat is worn, add a little valve sand for grinding until it is tight.
  • 3. Repair of the pump cover task plane: if the wear of the pump cover task plane is small, the wear trace can be eliminated by manual grinding, that is, put a little valve sand on the platform or thick glass plate, and then put the pump cover on it for grinding until the wear trace is eliminated and the task surface is flat. When the wear depth of the pump cover exceeds 0.1mm, it shall be repaired by turning first and then grinding. Repair of the automatic shaft bushing hole of the bag cage of the dust collector: the repair of the wear of the automatic shaft bushing hole on the pump cover is the same as that of the housing.
  • 4. The gear wear of gear pump is mainly at the tooth thickness, while the wear of gear end face and tooth top are relatively light. The gear is worn on one side at the tooth thickness, so the gear can be turned over 180 degrees. When the gear end face is worn, the end face can be ground flat and the connecting surface of the oil pump housing can be ground smooth to ensure that the clearance between the gear end face and the pump cover is within the specification.

Reasons for poor rotation of gear pump

  • ① Axial clearance or radial clearance is too small. Readjust and repair.
  • ② There is dirt in the pump. Disassemble to remove foreign matters.
  • ③ Incorrect assembly. The machining datum of the two pin holes of the gear pump is not the assembly datum. If the pin is driven in first and then the screw is tightened, the pump will not rotate. The correct method is to tighten the screws while rotating the gear pump, and finally drill the pin hole and drive the pin.
  • ④ The coaxiality of pump and engine coupling is poor. The coaxiality shall be within 0.1mm.
  • ⑤ The parts in the pump are not demagnetized. All parts must be demagnetized before assembly.
  • ⑥ The quality of needle roller sleeve is unqualified or the needle roller is broken. Repair or replace.
  • ⑦ The working oil outlet is blocked. Remove foreign matters.

Usual maintenance method of gear pump

When using the gear pump, we can’t avoid the wear of the gear pump, so there will be many problems, so we should learn the most common maintenance technology for the gear pump. If you have a problem, you can make an accurate judgment. Next, I’ll tell you about the most common maintenance technology:

  • 1. Maintenance of the working plane: if the wear of the working plane of the pump cover is relatively small, you can eliminate the wear marks by hand grinding, that is, put a little valve sand on the platform or thick glass plate, and then put the pump cover on it for grinding until the wear marks are worn off and the working surface is flat. If the wear depth of the working plane of the pump cover exceeds 0.1mm, it should be repaired by turning and grinding first.
  • 2. Maintenance of driving shaft bushing hole: the maintenance method for the wear of driving shaft bushing hole on the pump cover is the same as that for the wear of driving shaft bushing hole on the housing.
  • Repair of the inner cavity of the pump casing: after the inner cavity of the pump casing is worn, the inner cavity inlay method is adopted for repair, that is, after the inner cavity is lined with large, it is inlaid with cast iron or steel bushing. After inserting the sleeve, the inner cavity shall be lined to the required size, and the bushing protruding from the end face shall be ground off, which shall be flush with the joint surface of the pump housing.
  • 3. Maintenance of valve seat: there are two kinds of pressure limiting valves: ball valve and plunger valve. After the ball valve seat is worn, put a steel ball on the valve seat, and then gently tap the steel ball with a metal rod until the ball valve is close to the valve seat. If the valve seat is seriously worn, ream to remove the wear mark, and then use the above method to make it close. After the plunger valve seat is worn, add a little valve sand for grinding until it is tight.
  • The above is about the maintenance of some of the most basic parts of the gear pump. We may encounter different problems in other aspects in the process of application. We have to seriously explore these different problems and find out the causes of the problems.

Development direction of gear pump

With the growth of population and the development of economy, energy problem has been paid more and more attention, especially in China, energy conservation has become more and more important. In order to strengthen the energy-saving concept of enterprises, China may start a more severe price lever for production power consumption. Therefore, energy conservation has become an important direction for the development of gear pump.
As a main type of pump, gear pump has undergone many important developments and changes. Early gear pumps were all hydraulic. Due to the needs of environmental protection and energy saving, as well as the mature application of servo motor and the substantial decline in price, there are more and more all electric precision gear pumps in recent years. In order to analyze this development trend, I list the comparative characteristics:

  • The all electric gear pump has a series of advantages, especially in environmental protection and energy saving. It is reported that by the end of December 2014, the power saving of the more advanced all electric gear pump can reach 70%. In addition, due to the use of servo motor, the injection control accuracy is high, the speed is stable, and it can be adjusted at multiple levels. However, the service life of the all electric gear pump is not as good as that of the all hydraulic gear pump. In order to ensure the accuracy of the all hydraulic gear pump, the servo valve with closed-loop control must be used, and the servo valve is expensive, resulting in an increase in cost.
  • The full hydraulic gear pump has many unique advantages in forming precision and complex products. It has developed from the traditional single cylinder liquid filling type and multi cylinder liquid filling type to the two plate direct pressure type, of which the two plate direct pressure type is the most representative, but its control technology is difficult, the machining precision is high, and the hydraulic technology is difficult to master.
  • Electric hydraulic gear pump is a new type of gear pump integrating hydraulic and electric drive. It integrates the high performance of all hydraulic gear pump and the energy-saving advantages of all electric gear pump. This composite gear pump with the combination of electric and hydraulic has become the development direction of gear pump technology.

According to the process requirements of gear pump equipment, the power consumption of gear pump oil pump motor accounts for 50% – 65% of the power consumption of the whole equipment, so it has great energy-saving potential.

Source: China Pipe Fitting Manufacturer – Yaang Pipe Industry (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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