Abstract: The ordinary integral two-stage relief valve can not work steadily when its dimension is limited. To solve this problem, a mathematical model of two-stage relief valve is established and the stability criterion of the pilot valve is obtained. The criterion indicates that there is a matching relationship between the main valve size and the pilot valve size in integral two-stage relief valve. If the main valve size is too large or the pilot valve size is too small, the pilot valve will become unstable. A new type two-stage relief valve with a series damping orifice in the front chamber of pilot valve is proposed to achieve stable control of the pilot valve and main valve without increasing the volume of the relief valve. This damping orifice can avoid direct impact on the pilot valve core from the pilot input flow, and decrease the open loop gain of the pilot valve loop. Theoretical and experimental results show that the new type two-stage relief valve can work steadily and has a better pressure-flow characteristic with the extreme small size.

Key words: technology of instrument and meter, hydraulics, extreme small size, integral two-stage relief valve, stability, damping orifice