This series belongs to the pilot valve piston valve. From the main valve and pilot valve composed of two parts. Mainly by the main valve seat, the main valve plate, piston, springs and other parts. Mainly by the pilot valve seat, disc, diaphragm, spring, adjusting SPRINGS. Adjusting the spring pressure by adjusting the outlet pressure setting, the use of changes in outlet pressure sensing diaphragm, through the pilot valve opening and closing the main valve piston adjusting throttle flow area the size of the site to achieve vacuum regulator function. 
 This series of products based on the common valve made the following improvements to increase the piston area, changing the throttle structure and changed the seal in the form, structure and improvement of the pilot valve spring form of regulation to improve the following aspects of the product performance. 
 1, the increased pressure sensor on the export performance, improved sensitivity, greatly reduced due to changes in upstream pressure and flow changes in pressure caused by factors such deviation. 
 2, to improve the streamline distribution and reduce the noise. 
 3, the improvement of the sealing surface of the structure, extending the life of the sealing surface. 
 This product is mainly used for steam pipes for inlet pressure changes, a large steam pipe flow changes.