Repair method of drive shaft leak oil in pump

In the maintenance of hydraulic motors, the leakage of the transmission shaft often occurs, and many customers are helpless when facing this situation. In fact, anyone who knows the structure of the hydraulic motor can easily determine where the failure occurred. Today, Runfront briefly introduces several repair methods for the leakage of hydraulic motor drive shafts.


The transmission shaft of the hydraulic motor usually uses a lip seal ring as an oil seal when it protrudes from the housing. The oil seal is composed of an elastomer, a metal skeleton and a spring. The inner diameter is slightly smaller than the shaft diameter. The interference amount installed on the shaft against the inner lip holds the shaft surface. The spring is placed on the outer edge of the inner lip of the elastomer to increase the contact pressure between the lip and the transmission shaft and compensate for lip wear. This oil seal will not leak when shutting down, and the amount of leakage during work will not exceed 1 drop per hour. The standard product of this oil seal does not exceed 0.5MPa, the pressure-resistant type can generally reach 1 to 3MPa, and some brands can reach 10MPa, which also shows in disguise that the applicable working pressure is usually not high. The roughness of the contact between the shaft or sleeve and the oil seal should be small, and the contact surface should be coated with oil or grease during installation.

Leakage of the drive shaft after a long time use of a hydraulic motor is a common failure, usually due to wear and aging of the elastomer of the oil seal, or wear and rust at the contact between the shaft (or sleeve) and the oil seal. The latter can be repaired by grinding after welding, or the sleeve can be replaced; the oil seal and all O-rings must be replaced in principle after each disassembly. Long-term oil leakage of the transmission shaft often means that the service life of the pump or motor’s other wearing parts (seals, bearings, etc.) is approaching, and the wear and tear of the moving mating surfaces of the components may also be serious. The oil seal should be replaced.


There is another possibility that the oil seal is leaking because the oil pressure it bears is too high. The oil pressure on the hydraulic pump or motor drive shaft oil seal is the oil pressure on its bearings. Bearings are usually lubricated and cooled by oil leaking from the gap between moving parts; some plunger pumps with higher power, longer working time or higher ambient temperature rely on leaking oil to cool the bearing and the heat dissipation is not enough, so auxiliary pumps are needed The bearing flushing oil port of the input housing is used for cooling.

The oil leaking into the casing of the plunger pump and motor mainly comes from the plunger couple and the oil distribution plate (shaft), etc., and the drain of the valve assembly assembled with the pump and motor usually also enters the casing. All are equipped with drain pipes to lead these oils back to the tank. Some models used for open systems have a housing that communicates with the oil suction port, eliminating the need for a drain pipe. If imitating the hydraulic control valve, the special drain pipe can be called external drain, and the omitted drain pipe can be called internal drain. The maximum (absolute) oil pressure allowed for plunger pumps and motor housings is generally 0.2 to 0.5 MPa, and the maximum is not more than 1 MPa. The lower the speed and the drain pressure of the housing, the longer the life of the seal.

The leakage of the hydraulic motor drive shaft is usually caused by the leakage of the oil seal, and there are several reasons for the leakage of the oil seal. When we are repairing the hydraulic motor, we just need to find out the cause of the leakage of the oil seal to see if it is naturally worn too much or the hydraulic motor pressure problem has caused the oil seal to break. After finding out, depending on the situation, to see if it is replaced or repaired, it depends on the damage.

Post time: Jul-31-2020