Influence Of Internal Gear Pump's Floating Plate On Pump's Service Life And Efficiency

The greatest advantages of internal gear pump are: compact structure, small dimension, light weight, low sound level ,easy to reach high pressure compared with other types of pumpes. Its application cann't be replaced on some special occasion. Internal gear pump has a bright prospect.The floating plate, which has great impact on pump's service life and volumetric efficiency, is one of the most important components of internal gear pump. There are two applied forces acting on floating plate, one from the outlet port formed by the pinion, inner gear and filling piece, the other from the back-pressure cavity of floating plate. In order to analyse convinently, these two action area are simplified into two force functional points acting on each acting areas. The area, affected by pressure oil, between floating plate and gear teeth changes dynamically with gears' meshing. And the area's equivalent area and force functional point also change dynamically, which mean they are variables. The action area on the floating plate's back-pressure cavity is a fixed value, and the area's equivalent area and force functional point are also fixed value, which mean they are constants. When the pump working, these two action areas and two force functional points will be compared. The result is that there will be some time in which those two equivalent areas aren't equal and two force functional points aren't coincident. If the two force functional points aren't coincident, the floating plate will be inclined. Once it happened, the abrasion between gear pair and floating plate would be badly. Then the pump's service life will be reduced. If the two equivalent areas aren't equal, the differential value between those applied forces will make the floating plate axial shifting, then the axial clearance between the gear pair and floating plate will be changed . As a result, the pump's volumetric efficiency will also change dynamically.The paper gives study on the floating plate using some knowledge of moment balance and force equilibrium. It indicate that, in order to increase the pump's service life, the force functional point's coordinate value of the back-pressure cavity of floating plate must be located on some special point of the fitting curve formed by other force functional points from the outlet port. The floating plate must be in the state of excessive balance, which means that the applied force from the back-pressure cavity of floating plate is larger than the one from the outlet port. In this state, the floating plate can compensate the axial clearance between gear pair and floating plate automatically. The axial clearance's impact on the pump's volumetric efficiency is greatest. According to the analysis results, the value of the axial clearance shuld range from 30μm to 40μm. The conclusions of the paper will present useful tool for the designing and optimization of the internal gear pump.