What is a Hydraulic Pump?

A hydraulic pump is a power component of a hydraulic system. It is driven by an engine or an electric motor. It sucks oil from a hydraulic oil tank, forms pressure oil, and sends it to an actuator. The hydraulic pump is divided into gear pump, plunger pump, vane pump and screw pump according to the structure. ^[1]

Chinese name: Hydraulic pump
Foreign name: Hydraulic pumps

Drive: Engine or electric motor
Structure: Gear pump, piston pump, vane pump and screw pump
Nature: Hydraulic component

Introduction to Hydraulic Pump

A hydraulic component that provides pressurized liquid for hydraulic transmission is a type of pump. Its function is to convert the mechanical energy of power machines (such as electric motors and internal combustion engines) into pressure energy of liquids. There are many factors that affect the service life of hydraulic pumps, in addition to the pump's own design and manufacturing factors, and the selection of some components related to the use of the pump (such as couplings, oil filters, etc.), and operations during commissioning.

The working principle of a hydraulic pump is that movement causes a change in the volume of the pump cavity, thereby compressing the fluid so that the fluid has pressure energy.

A condition that must be present is a change in the sealed volume of the pump cavity.

Classification of hydraulic pump

Types of common hydraulic pumps:

1. According to whether the flow rate can be adjusted, it can be divided into: variable pump and fixed displacement pump. The output flow that can be adjusted according to needs is called a variable pump, and the flow that can not be adjusted is called a fixed displacement pump.

2. According to the common pump structure in the hydraulic system, it is divided into three types: gear pump, vane pump and plunger pump.

Gear pump: Smaller size, simpler structure, less strict requirements for oil cleanliness, and cheaper price; but the pump shaft is subject to unbalanced force, severe wear, and large leakage.

Vane pump: Divided into double acting vane pump and single acting vane pump. The pump has uniform flow, stable operation, low noise, higher operating pressure and volumetric efficiency than a gear pump, and a more complex structure than a gear pump.

Internal structure of hydraulic pump

Plunger pump: high volumetric efficiency, small leakage, can work under high pressure, mostly used in high-power hydraulic systems; but complex structure, high requirements for materials and processing accuracy, expensive, and high oil cleanliness requirements.

Generally, the plunger pump is used when the gear pump and vane pump cannot meet the requirements. There are some other forms of hydraulic pumps, such as screw pumps, but the applications are not as common as the three above.

Features of hydraulic pump

Made of aluminum alloy, high strength, corrosion resistance, light weight, suitable for operation in various environments.

The two-speed feature reduces the number of pressures, quickly enters the load power state in the low-pressure room, and immediately converts to high pressure, shortening each operation cycle.

Equipped with a pressure regulating valve, which can adjust the control and set the working pressure. composition

Vane pumps often used in the hydraulic machinery industry (2 photos)

Hydraulic pump coupling

1.Coupling selection

Hydraulic pump drive shaft cannot bear radial force and axial force, so it is not allowed to install pulleys, gears and sprocket directly on the shaft end.

Couplings are usually used to connect the drive shaft and the pump drive shaft. If due to manufacturing reasons, the coaxiality of the pump and the coupling exceeds the standard, and there is a deviation during assembly, the centrifugal force will increase as the speed of the pump increases, and the coupling will deform. A vicious cycle is caused, which results in vibration noise, which affects the service life of the pump. In addition, there are influencing factors such as loose coupling pins that are not fastened in time, and rubber ring wear that has not been replaced in time.

2. Assembly requirements for couplings

Coaxiality error of two axes of rigid coupling 0.05mm

Coaxiality error of the two shafts of the elastic coupling 0.1mm

Angle error of two axes <1 °;

The distance between the drive shaft and the pump end should be 5-10mm;

Hydraulic pump hydraulic oil tank

1.Selection of hydraulic oil tank

The main role of the hydraulic oil tank in the hydraulic system is to store oil, dissipate heat, separate air contained in the oil, and eliminate foam. The choice of fuel tank must first consider its capacity

The volume of the general mobile equipment is 2 to 3 times the maximum flow rate of the pump, and the fixed equipment is 3 to 4 times. Secondly, the oil level of the fuel tank is considered. After the cylinder is retracted, the oil level must not be higher than the maximum oil level. Finally, considering the structure of the fuel tank, the partition in the traditional fuel tank cannot play the role of sedimentation. A vertical partition should be installed along the longitudinal axis of the tank. There is a space between one end of the partition and the end plate of the fuel tank to make the two sides of the partition communicate with each other. The inlet and outlet ports of the hydraulic pump are arranged on both sides of the disconnected end partition to maximize the distance between the oil inlet and the oil return. The hydraulic oil tank plays a role of heat dissipation.

2.Installation of hydraulic oil tank

According to the different installation positions, it can be divided into upper, side and lower.

The upper type oil tank installs the hydraulic pump and other devices on the upper cover plate with better rigidity, and its structure is compact and the most widely used. In addition, heat radiating fins can be cast on the fuel tank shell to enhance the heat dissipation effect, which increases the service life of the hydraulic pump.

The side-mounted fuel tank is a device that installs hydraulic pumps and other devices next to the fuel tank. Although it covers a large area, it is easy to install and maintain. It is usually used when the system flow rate and fuel tank capacity are large, especially when one fuel tank supplies multiple hydraulic pumps Used during fueling. Because the oil level of the side-mounted tank is higher than the suction port of the hydraulic pump, it has a better oil absorption effect.

The lower type fuel tank puts the hydraulic pump under the fuel tank, which not only facilitates installation and maintenance, but also greatly improves the suction capacity of the hydraulic pump.

Hydraulic pump oil filter

Selection of oil filter

Generally, the impact of pollutants with a particle diameter of less than 10 m on the pump is not obvious, but greater than 10 m, especially above 40 m, has a significant impact on the service life of the pump. Solid contaminated particles in hydraulic oil can easily aggravate the surface of relatively moving parts in the pump. To this end, oil filters need to be installed to reduce the degree of oil pollution. Filtration accuracy requirements: 10 ~ 15 m for axial piston pumps, 25 m for vane pumps, and 40 m for gear pumps. The contaminated wear of the pump can be controlled within the allowable range. High-precision oil filters are increasingly used, which can greatly extend the service life of hydraulic pumps.

Working principle of hydraulic pump

It is a kind of hydraulic component that provides pressurized liquid for hydraulic transmission. It is a kind of pump. Its function is to convert the mechanical energy of power machines (such as electric motors and internal combustion engines) into pressure energy of liquids. The figure shows the working principle of a single plunger pump. The cam is rotated by a motor. When the cam pushes the plunger to move upward, the sealing volume formed by the plunger and the cylinder body is reduced, and the oil is squeezed out of the sealed volume and discharged to the required place through the check valve. When the cam rotates to the lower part of the curve, the spring forces the plunger downward to form a certain degree of vacuum, and the oil in the fuel tank enters the sealed volume under the effect of atmospheric pressure. The cam continuously raises and lowers the plunger, the sealing volume is periodically reduced and increased, and the pump continuously sucks and discharges oil.

Hydraulic pump performance parameters

The hydraulic pump is the power component of the hydraulic system. Its function is to provide pressure oil to the hydraulic system. From the perspective of energy conversion, it will convert the mechanical energy output by the prime mover (such as the engine) into the pressure energy of the liquid that is easy to transport. Hydraulic motor is an actuator. It can convert the pressure energy of the input liquid into the mechanical energy of the output shaft, which is used to drag the load to do work. According to the structural form, the hydraulic pump and the hydraulic motor can be specifically classified into a gear type, a vane type, a plunger type and the like.

Hydraulic pump pressure

The working pressure of a hydraulic pump refers to the pressure of the oil output (or input) by the pump (or motor) during actual work, which is determined by the external load.

Rated pressure refers to the highest pressure that can be continuously operated according to the test standards under normal working conditions. Its size is limited by the life. If it exceeds the rated pressure, the life of the pump (or motor) will be shorter than the designed life. When the working pressure is greater than the rated pressure, it is said to be overloaded.

2.Speed

Working speed refers to the actual rotation speed of the pump (or motor) during work.

Rated speed refers to the highest speed that can continuously run for a long time under the rated pressure. If the pump works above the rated speed, it will cause insufficient oil absorption, generate vibration and large noise, and parts will suffer from cavitation damage and reduce the life.

The minimum stable speed is the minimum speed allowed for normal operation of the motor. At this speed, the motor does not crawl.

3.Displacement and flow

Displacement refers to the volume of liquid discharged (or inputted) obtained by the change of the geometric dimensions of the sealed cavity for each revolution of the pump (or motor). The common unit is ml / r (ml / rev). The displacement can be changed into a variable pump (or variable motor) by adjusting, and the displacement cannot be changed into a fixed displacement pump (or fixed displacement motor).

The actual flow is the flow at the outlet (or inlet) when the pump (or motor) is operating. Due to the internal leakage of the pump, its actual flow is less than the theoretical flow. Because the motor itself also has internal leakage, in order to achieve the specified speed, in order to compensate for the leakage, the actual input flow must be greater than the theoretical flow.

4. Efficiency

Volumetric efficiency refers to the ratio of the actual flow rate to the theoretical flow rate of a hydraulic pump. For a hydraulic motor, it is the ratio of its theoretical flow to actual flow.

Mechanical efficiency refers to the ratio of the theoretical torque to the actual input torque of the hydraulic pump. For a hydraulic motor, the actual output torque is the torque after the theoretical torque overcomes friction, so its mechanical efficiency is the ratio of the actual output torque to the theoretical torque.

The total efficiency is the ratio of the output power of the pump (or motor) to the input power. The total efficiency is equal to the product of volumetric efficiency and mechanical efficiency.

Hydraulic pump repair and maintenance

Causes of failure: (1) The oil level of the hydraulic oil tank is too low;

Exclusion method: add hydraulic oil

Cause of failure: (2) Hydraulic oil is not used according to the season;

Exclusion method: Generally applicable to 46 # hydraulic oil (or 68 #) without special replacement, consider using 32 # when winter is extremely cold in the north

Failure reason: (3) the oil inlet pipe is severely blocked by dirt;

Exclusion method: remove foreign objects in the tube

Causes of failure: (4) The oil seal of the driving gear of the oil pump is damaged, and air enters the hydraulic system;

Remedy: Replace worn or damaged oil seals and O-rings

Cause of failure: (5) The oil pump inlet and outlet joints or elbow joints O -shaped seals are damaged, the elbow joint fastening bolts or the inlet and outlet pipe nuts are not tightened, and air enters the hydraulic system;

Remedy: Replace the O-ring, tighten the bolt or nut at the joint

Cause of failure: (6) Internal leakage of oil pump, aging of seal ring;

Remedy: Replace the seal

Causes of failure: (7) The end faces of the oil pump or the end faces of the main and driven gear bushes are worn or scratched, and the unevenness of the end faces of the two bushings is extremely poor;

Remedy: Replace the worn gear oil pump or oil pump shaft sleeve. When the wear is slight, smooth the end surface on the flat plate. The allowable error of its unevenness is 0.03mm; the end face of the upper sleeve is lower than the pump body, and the upper plane (normal value is less than 2.5 ~ 2.6mm). If it is too bad, the lower sleeve should be added with 0.1 ~ 0.2mm copper sheet to compensate. Should be placed on the rear sleeve

Failure reason: (8) Internal leakage caused by incorrect assembly of internal parts of the oil pump;

Remedy: Unloading disc and seal ring must be installed in the oil chamber, so that the two shaft sleeves can maintain balance. The elasticity of the guide wire should be able to twist the upper and lower shaft sleeves toward the driven gear at the same time by a slight angle, so that the machining planes of the two shaft sleeves of the main and driven gears are closely fitted; Side to eliminate the harmful dead volume when the gear meshes; before pressing the self-tightening oil seal, it should be coated with a layer of lubricating oil. Also pay attention to the oil blocking edge facing the front cover, which cannot be reversed; before installing the pump cover, you must Pour a small amount of hydraulic oil into the pump casing and turn the meshing gear by hand

Failure reason: (9) "Left-handed" oil pump with "right-handed", causing the oil seal of the skeleton to be damaged;

Remedy: "Right-handed" pumps cannot be installed on "Left-handed" machines, otherwise the skeleton oil seal will be damaged;

Cause: (10) The hydraulic oil is too dirty.

Remedy: Clean the system and replace the hydraulic oil.

Cause of failure: (11) The filter of the pump is blocked by dirt and cannot function as oil filter

Remedy: Remove the dirt from the filter with clean cleaning oil.

Cause of failure: (12) Insufficient oil level, oil suction position is too high, oil suction pipe is exposed to oil surface:

Remedy: Add oil to the oil level and lower the oil suction position.

Cause of failure: (13) There is no paper pad on both sides of the pump body and the pump cover; the pump body and the pump cover are not sealed vertically:

Exclusion method: suction air when rotating: add paper pad between pump body and pump cover; pump body is ground on flat plate with emery, so that the vertical error between pump body and pump cover does not exceed 0.005mm, tighten the connection between pump body and pump cover There must be no leakage.

Cause of failure: (14) The drive shaft of the pump is not concentric with the motor coupling, and there is twisting friction:

Remedy: Adjust the concentricity of the coupling between the pump and the motor so that the error does not exceed 0.2mm.

Reason for failure: (15) The meshing accuracy of the pump gear is not enough:

Remedy: achieve gear meshing accuracy on the gear.

Cause of failure: (16) The oil seal skeleton of the pump shaft falls off and the pump body is not sealed:

Remedy: Replace qualified pump shaft oil seal.