(1) There is air in the oil pump. This fault usually occurs when a new pump is installed. When starting a new pump, oil should be added to the pump to lubricate the pump's bearings, plunger and cylinder.
  Solution: Open the oil pump filling port when the pump is running, so that the air in the pump can be discharged from the filling port.

(2) The oil level of the fuel tank is too low, and the oil suction pipe is blocked, which increases the oil suction resistance of the pump, causing the pump to suck empty or the oil inlet pipe to leak air, and the pump sucks in air.
Treatment method: add sufficient oil; clean the filter, dredge the intake pipe; check and tighten the connecting screws of the oil intake pipe section.
(3) Improper installation of the oil pump and the motor, that is to say, the concentricity of the pump shaft and the motor shaft is inconsistent, causing the oil pump bearing to be subjected to radial force to generate noise.
Solution: Check and adjust the concentricity of the oil pump and motor installation.
(4) The viscosity of the hydraulic oil is too large, which reduces the self-priming capacity of the pump and the volumetric efficiency. Treatment method: choose hydraulic oil with appropriate viscosity, if the oil temperature is too low, use a heater.