Abstract: The leakage of the clearance of the piston pair is the main factor affecting the volumetric efficiency of the piston pump, and the thermal-pressure coupling deformation of the micron clearance of the piston pair can not be ignored under ultra-high pressure.Based on the thermal-fluid-structure coupling method, the dominant pressure deformation model and the thermo-compression coupling deformation model were established to simulate the differential pressure flow in the two-dimensional axisymmetric model of the piston pair with 5 μm unilateral clearance height. The results show that when the inlet pressure of the piston pair is 110 MPa, the compressive deformation is dominant at the inlet of the clearance, and the unilateral clearance increases by more than 4 μm, while the thermal deformation is dominant at the outlet of the clearance, and the unilateral clearance decreases by 1.1 μm.The clearance leakage of the piston pair is 4 times as much as that of the piston pair without deformation under the model dominated by compression deformation. The clearance leakage of the piston pair calculated by thermal-pressure coupling deformation model is 1.3 times that of the piston pair without deformation.The research results provide a method for accurately predicting the clearance leakage flow of the piston pair of the ultra-high pressure water pump.

Key words: ultra-high pressure water pump, clearance of piston pair, pressure deformation, thermal-pressure coupled deformation, time-average clearance leakage ratio