The hydraulic pump is the energy device of the hydraulic system of the excavator. It converts the mechanical energy of the motor into hydraulic energy and outputs flow and pressure. It occupies a very important position in the hydraulic system. If the hydraulic pump fails, it will affect the normal operation of the entire hydraulic system. This article mainly introduces the causes and troubleshooting methods of hydraulic pumps for excavators.

Pressure can’t rise

Reason 1: The oil pump is not oiled or the flow is insufficient.

Remedy: Fill the pump with working oil.

Reason 2: The adjustment pressure of the overflow valve is too low or malfunctions.

Remedy: re-adjust the pressure of the overflow valve or repair the overflow valve.

Reason 3: There is a leak in the system.

Remedy: check the system, repair leaks

Reason 4: The pump cover screws are loose due to long-time vibration of the oil pump.

Remedy: Tighten the screws appropriately.

Reason 5: The suction pipe is leaking.

Remedy: check each connection, and seal and tighten it.

Reason 6: Insufficient oil absorption.

Remedy: Fill the pump with working oil.

Reason 7: Improper adjustment of variable pump pressure.

Remedy: readjust to the required pressure.

Insufficient oil supply of hydraulic pump

Fault diagnosis: the outside air enters the working cavity of the plunger pump and the displacement is reduced.

Analysis of the cause of the failure: As the working environment of the excavator is very harsh, it is very easy to break the oil suction pipe of the plunger pump or the sealing of the oil suction port in this environment, which causes the pump to suck in air. When the plunger pump is in operation, if the oil in the plunger working chamber enters air, when the plunger is at the oil pressure port position, the plunger will pressurize the oil and air in the chamber.

When the plunger moves to the bottom of the cylinder bore, there will always be part of the remaining volume at the bottom, that is, part of the pressurized oil is retained in the remaining volume of the cavity. When the plunger continues to move to the suction port position, as the internal volume of the cavity increases, the internal oil pressure decreases, and the air trapped in the remaining volume expands, so that part of the volume in the working cavity will be occupied by this part of the air. Occupy, so that the actual oil absorption of the plunger pump is reduced. When the air entering the oil reaches a certain amount, it will cause insufficient oil supply to the system or even no oil supply. Furthermore, if the hydraulic oil cannot flow into the suction port in time, cavitation will occur when the pump sucks oil 1:3, which will cause premature damage to the plunger seal and cavitation of the plunger cylinder wall. Therefore, corresponding measures must be taken to reduce or prevent air from entering the hydraulic system.

Elimination method:

1.Make sure that there is no leakage at the connections of all imported pipelines. To ensure a good seal, all pipe joints should be tightened; for plunger pumps, a tighter sealing device must be provided.

2.Prevent rupture or flattening of the suction hose. Try to control the flow rate of the liquid in the suction port to prevent the pressure of each point in the suction pipe from being lower than the atmospheric pressure and forming a vacuum, causing the rubber hose to leak, suck and invade the air.

3.Control the oil level of the fuel tank. Under normal circumstances, the vertical distance between the lowest oil level of the fuel tank and the suction port should be less than 0.5m; if the system permits, the height of the oil level in the fuel tank should be higher than the suction port of the pump, and the end of the oil return pipe of the hydraulic system should always be below the oil level , This can avoid the formation of air bubbles.

4.If there are a lot of bubbles in the fuel tank, they should be removed in time. If there is a considerable amount of air in the oil, loosen the pipe joint at the outlet of the plunger pump to discharge the air in the pump.