how to solve the output faults of Rexroth piston pumps and oil pumps?

Detailed Explanation of Output Fault Causes and Solutions of Rexroth Piston Pump

During the maintenance of Rexroth Piston Pumps, 

three common transmission faults are found in Rexroth piston pumps: insufficient flow or no flow, flow fluctuation, and abnormal working pressure. 

Generally speaking, how can these situations be detected and handled? 

The following text will introduce the situations where these three different output faults occur.

I. Firstly, the Rexroth hydraulic pump does not output flow and does not output oil.

Reasons:
Excessive rotation speed of the pump, too low liquid level in the oil tank, air leakage in the oil inlet pipe, blockage of the oil filter, etc. 

may all lead to excessive resistance in the oil suction pipeline or insufficient oil replenishment.
(2) Excessive leakage. It is caused by too large clearance of the pump and poor sealing. 

For example, the oil distribution plate is scratched by metal fragments, iron filings, etc., and there is end face oil leakage; 

the sealing surface of the check valve in the variable mechanism does not fit well, 

and there are sand holes or grinding marks on the supporting surfaces of the pump body and the oil distribution plate. 

The damaged part of the pump can be determined by detecting the mixed-phase impurities in the hydraulic oil of the pump body.
(3) The inclination angle of the swash plate is too small, resulting in a small displacement of the pump. 

The variable piston needs to be adjusted to increase the inclination angle of the swash plate. 

When the displacement at the middle position is not zero, the inclination angle of the swash plate of the variable Axial Piston Pump is zero at the middle position, and the output flow of the pump should be zero at this time. 

However, sometimes there is a phenomenon that the middle position deviates from the midpoint of the adjustment mechanism, and there is still flow output at the middle position. 

The reason is that the position of the controller deviates, is loose or damaged, and it needs to be re-zeroed, tightened or replaced. 

Insufficient angle maintaining force of the pump and wear of the inclination angle trunnion will also cause this phenomenon.

II. Fluctuation of output flow

(1) The fluctuation of output flow is related to many key factors. For variable pumps, it can be considered that the control of the variable mechanism is not good. 

For example, foreign objects enter the variable mechanism, leaving steps, grinding marks, scratches, etc. on the control piston, 

resulting in unstable movement of the control piston. Insufficient energy of the amplifier or damaged parts, 

and poor performance of the damper of the control piston with a spring will all lead to unstable movement of the control piston.
(2) Unstable flow is usually accompanied by pressure fluctuations. 

Generally, for this type of fault, the hydraulic pump needs to be disassembled, the damaged parts need to be replaced, 

the resistance needs to be increased, and the spring stiffness and the control pressure need to be enhanced.

III. Abnormal output working pressure

The output working pressure is too low.
① When the pump is in the self-priming state, if there is air leakage in the oil inlet pipeline or there is a large leakage in components such as the hydraulic cyLinder, 

check valve, and directional valve in the system, the pressure cannot rise. The air leakage point needs to be found, tightened, 

and the sealing parts need to be replaced to increase the pressure. If the relief valve has a fault or the adjusted pressure is low, 

the system pressure cannot rise either, and the pressure should be readjusted or the relief valve should be overhauled. 

If there is a large leakage due to the deviation between the cylinder block and the distribution plate of the hydraulic pump, and the cylinder block may crack seriously, 

the matching surface should be reground or the hydraulic pump should be replaced.
② The output working pressure is too high. If the load of the control loop continues to increase, 

the working pressure of the pump will also continue to increase, which is normal. 

If the load is certain and the pressure of the pump exceeds the required pressure value of the load, the hydraulic components other than the pump, 

such as the directional valve, pressure valve, transmission device, and oil return pipeline, should be checked. 

If the maximum pressure is too high, the relief valve should be adjusted.

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