Advantages: simple and compact structure, small size, light weight, good processability, low price, strong self-suction, insensitive to oil pollution, large speed range, impact-resistant load, convenient maintenance and reliable operation.

Disadvantages: radial force imbalance, large flow artery, high noise, low efficiency, poor interchangeability of parts, difficult to repair after wear, can not be used for variable pump.

Sleepy oil phenomenon

Reason: During the operation of the involute gear pump, the hydraulic fluid is sealed between the teeth due to the closed volume at the intersection of the gears. As shown in the figure, it is called trapped oil, due to hydraulic pressure. The incompressibility of the oil will cause extreme vibration and noise of the external gear, which will affect the normal operation of the system.

Measures: opening and unloading the groove on the front and rear cover plates or the floating bushing, and the principle of opening the unloading groove: the distance between the two grooves is the minimum dead volume, and the closed volume is connected to the pressure oil chamber from the large change hour, and the dead volume is closed. When it is small, it is connected to the oil suction chamber.

Leakage

The leakage of the gear pump is large, and the leakage path of the external gear has the following three points: one is the gear head clearance, the second is the gap measurement, and the third is the meshing gap.

The leakage of the end face gap is large, accounting for 80%-85% of the total leakage. When the pressure increases, the former will not change, but the deflection of the latter is greatly increased. This is the main reason for the leakage of the external gear pump, volumetric efficiency. It is not suitable for use as a high pressure pump.

Solution: Face clearance compensation uses static pressure balancing measures to add a compensation part between the gear and the cover, such as floating bushings and floating side plates.

Unbalanced force

The right side is the pressure oil chamber, the left side is the oil suction chamber, the pressure of the two chambers is unbalanced; in addition, the pressure chamber is leaked due to the tip of the tooth, and the pressure is decreasing. The two unbalanced pressures act on the radial unbalanced pressure of the gear and the shaft. The higher the oil pressure, the greater the force, the accelerated bearing wear, the lower bearing life, the bending of the shaft, and the increased wear of the tooth top and the shaft hole.

Preventive measures: Use a pressure balance tank or reduce the pressure oil chamber.