Abstract: In view of anomalous and non reproducible test results of jet pipe servovalves under high temperature, it is proposed that the valve body, sleeve and spool can be simplified into regular metal frames, based on the deformation rule of regular metal frame with residual stress under variable temperature field, change of couples' fitting state and its mapping relationship with servovalve failures are analyzed. It shows that in high temperature environment, radial clearance between aluminum valve body and steel sleeve enlarges, and the sleeve obtains some axis space moving randomly, which destroys the fitting relationship between the jet-pipe nozzle and the receiver held in the sleeve, leading to anomalous and non reproducible test results; radial clearance between steel spool and sleeve with grinding burn on the mating surface reduces, which is likely to block and result in flow fluctuation or jump of the valve. Improvements include changing the tail of the receiver into a dowel, which connects the valve body and sleeve as a whole; adding lock bolts to prevent "pull out" of the receiver by expansion and contraction of the valve body under long term temperature alternation; adding butterfly spring inner beside the lock ring, ensures its pre-compression is greater than the elongation difference between the aluminum valve body and the steel sleeve, and eradicates the sleeve's axis free space; increasing the flow rate of coolant to enhance heat dissipation in grinding, and add a hardness screening process for the mating surface of spool and sleeve. Elevated temperature experimental results are in good agreement with the theoretical analysis.

Key words: anomalous characteristics, couples matching, high temperature, jet pipe servovalve, restraining measure