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| The minimal trapped-oil pressure of expansion stage in external gear pump |
| Li Yulong |
| Industrial Manufacturing College, Chengdu University, Chengdu, Sichuan 610106, China |
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Abstract To overcome the limitations of testing and simulation, an analytic formula on minimal trapped-oil pressure in an external gear pump was tentatively established. For the expansion phase of trapped-oil, both cases of small backlash value and large backlash value, the long hole flow formula was applied to calculate the differential pressure flow through backlash. The leak path was simplified to calculate the axial leak flow from trapped-oil zone. The minimal trapped-oil pressure was calculated in the transient position that the expansion ratio of trapped-oil volume was equal to trapped-oil leak flow, that is to say, the change ratio of trapped-oil pressure with time was zero. The calculated results were then compared with the experimental results of the existing literature. The results show that, the position of minimal trapped-oil pressure was around the opening of relief groove, when in the inside, the negative minimal trapped-oil pressure would occur; while in the outside, the minimal trapped-oil pressure would approach closely the inlet-pressure; the minimal trapped-oil pressure was contributed by the outlet-pressure and rotation speed, among which, the minimum trapped-oil pressure was in a negative linear relationship with speed and a positive linear relationship with outlet-pressure; the overall offset of two relief grooves to inlet side was reasonable, etc. It can be finally concluded that, with the established analytic formula, the minimal trapped-oil pressure and its position can be promptly found without going through a large number of processes. Thus, the accumulated errors from process simulation are reduced and the minimal trapped-oil pressure is more accurate.
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Received: 26 December 2012
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