A lift valve communicating with a compression chamber of a variable capacity screw compressor is set forth including a valve housing, a piston reciprocally received within the valve housing, a shaft having a first end connected to the piston and a second end extending from the housing. The valve further...http://www.google.com.hk/patents/US5556271?utm_source=gb-gplus-share專利 US5556271 - Valve system for capacity control of a screw compressor and method of manufacturing such valves
