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Understanding of the overall structure of hydraulic pumps for excavators

Construction machinery structure recognition-excavator hydraulic pump overall structure recognition


Hydraulic pump is a kind of hydraulic component that provides pressure liquid for hydraulic transmission and 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 liquid pressure energy. There are many factors that affect the service life of a hydraulic pump. In addition to the pump’s own design and manufacturing factors, it is also related to the selection of some components related to the use of the pump (such as couplings, oil filters, etc.), and the operation during trial operation.


The hydraulic pump is the power component of the hydraulic system, which converts the mechanical energy input by the prime mover into pressure energy output, and provides pressure oil for the actuator. For the hydraulic pump to work normally, three necessary conditions must be met: it must have a closed volume composed of moving parts and non-moving parts; the size of the closed volume changes periodically with the movement of the moving parts, and the volume changes from small to large When the airtight volume is increased to the limit, it must be separated from the oil suction chamber before turning to oil discharge; when the airtight volume is reduced to the limit, it must be separated from the oil discharge chamber first. Then it switched to oil absorption. The single plunger pump achieves this requirement through two one-way valves.


1) According to whether the displacement can be adjusted, it can be divided into: variable pump and fixed pump. The output displacement can be adjusted according to needs is called a variable pump, and the displacement cannot be adjusted is called a quantitative pump.

       2) According to the commonly used pump structure in hydraulic systems, it can be divided into three types: gear pump, vane pump and plunger pump.

     (1) Gear pump: small in size, simple in structure, less demanding on oil cleanliness, and cheaper; but the pump shaft is subject to unbalanced forces, severe wear and large leakage.

(2) Vane pump: divided into double-acting vane pump and single-acting vane pump. This kind of pump has uniform flow, stable operation, low noise, higher working pressure and volumetric efficiency than gear pumps, and more complex structure than gear pumps.


(3) Plunger pump: high volumetric efficiency, low leakage, can work under high pressure, mostly used in high-power hydraulic systems; but the structure is complex, the material and processing accuracy requirements are high, the price is expensive, and the oil cleanliness requirements are high.

       Generally, plunger pumps are used when gear pumps and vane pumps cannot meet the requirements. There are other types of hydraulic pumps, such as screw pumps, but their applications are not as common as the above three types. The main pump of excavator generally adopts plunger pump.


The principle of hydraulic pumps is actually not complicated. You can find such examples everywhere in life. For example, syringes for injections and hand pumps for pumping water. For water pumps, there are two main points of work:

     (1) The piston draws back, sucks in water, pushes out, and draws water;

     (2) The greater the range of piston movement, the greater the amount of suction and drainage.

      For the plunger hydraulic pump used in the excavator, the main tasks are as follows:

     (1) The plunger reciprocates on the cylinder, sucking oil when it retreats, and draining oil when it moves forward;

     (2) A plunger pump has nine plungers, which can pump out hydraulic oil in turn;

     (3) The stroke of the plunger changes by changing the angle of the swash plate, thereby changing the oil discharge.


A plunger pump is mainly composed of a main shaft, a cylinder block, a plunger, a valve plate and a swash plate. The main shaft of the pump is splined to a cylinder called the cylinder block. The cylinder block is equipped with a crescent-shaped disc called the valve plate. , The oil port on the valve plate is arranged to pass the oil suction port when the plunger is retracted, and pass the oil outlet when the plunger advances. There is a part with a disc supporting the plunger called a swash plate. The angle of the swash plate can be adjusted up or down to change the stroke of the plunger, which also changes the amount of hydraulic oil discharged. The greater the angle of the swash plate, the greater the amount of hydraulic oil discharged. When the input shaft rotates, the cylinder body also rotates. When the swash plate is tilted, the plunger in the cylinder moves in a circular motion with the cylinder body while doing axial reciprocating motion, so that when the plunger passes through the suction port, it sucks oil. , When passing the oil outlet, drain the oil.