Influence of temperature on null position pressure characteristics of flapper-nozzle servo valve

At different working temperature, Flow coefficients of the orifices in the pilot state of flapper-nozzle servo valve will change due to the changes of hydraulic oil properties. It may change the pressure distribution in the valve, which affect the dynamic performance of servo valve directly. Based on test data, piecewise functions were set up to describe the relation between flow coefficient and flow number for the orifices. Then combined with the calculations of hydraulic oil parameters, the variation of null position control pressure of flapper-nozzle servo valve was simulated while working temperature changed from −40°C to 135°C. According to the simulation results, when working temperature is lower than 80?, the control pressure of servo valve will change along with temperature, but a proper drain orifice may reduce the pressure variation.