Hydraulic pump is the energy device of excavator hydraulic system. It converts the mechanical energy of motor into hydraulic energy and outputs flow and pressure. It plays a very important role in the hydraulic system. If the hydraulic pump fails, the normal operation of the whole hydraulic system will be affected. This paper mainly introduces the fault causes and troubleshooting of insufficient oil supply of excavator hydraulic pump.
1. Fault diagnosis
External air enters the working chamber of the plunger pump, resulting in a reduction in displacement.
2. Failure cause analysis
Because the working environment of the excavator is very bad, in this environment, it is very easy to break the oil suction pipe of the plunger pump or the seal at the oil suction port is not tight, resulting in the pump sucking in air. During the operation of the plunger pump, if the oil in the working chamber of the plunger enters air, when the plunger is at the oil pressure port, the plunger will pressurize the oil and air in the chamber.
When the plunger moves to the bottom of the cylinder block hole, there will always be part of the remaining volume at the bottom, that is, some pressurized oil remains in the remaining volume in the cavity. When the plunger continues to run to the oil suction port, with the increase of the volume in the chamber, the internal oil pressure decreases, and the air retained in the remaining volume expands. In this way, part of the volume in the working chamber will be occupied by this part of the air, which reduces the actual oil suction of the plunger pump. When a certain amount of air enters the oil, it will cause insufficient or even no oil supply to the system. Moreover, if the hydraulic oil cannot flow into the oil suction port in time, the pump suction 1:3 will produce cavitation, resulting in premature damage of 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.
3. Troubleshooting
1) Make sure that there are no leaks at the connections of all inlet pipes. To ensure good sealing, all pipe joints shall be tightened; For the plunger pump, it must have a tight sealing device.
2) Prevent the oil suction hose from cracking or flattening. Try to control the flow rate of the liquid at the oil suction port to prevent the vacuum formed by the pressure at each point of the oil suction pipeline being lower than the atmospheric pressure, resulting in air leakage, flattening and air intrusion of the rubber hose.
3) Control the oil level height of the oil tank. Generally, the vertical distance between the lowest oil level of the oil tank and the oil suction port shall be less than 0.5m; If the system permits, the height of the oil level in the oil tank should be higher than the oil suction port of the pump, and the end of the oil return pipe of the hydraulic system is often below the oil level, so as to avoid bubbles.
4) If there are a lot of bubbles in the oil tank, they should be eliminated 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.
