Abstract: In order to test the time constant value τ of dynamic pressure feedback servo valves, an approach based on frequency sweep is presented. The transfer function is established between the load differential pressure and feedback differential pressure. The transfer function is an expression about τ.So the time constant value can be calculated through the transfer function. A testing equipment is designed, and the amplitude frequency characteristic of the transfer function can be acquired through it. In this equipment, an alternating load with constant amplitude and incremental frequency is generated through a load servo valve. A digital controller is designed to realize the load amplitude value control. The test result shows that the test procedure is feasible, and the data obtained is accurate and reliable. The test method designed in this article can meet engineering requirements.

Key words: dynamic pressure feedback, characteristic test, time constant, servo, valves