It is also called pneumatic lock valve, is auxiliary components of pneumatic unit combination instruments. When the gas supply system does not work, the Paul-bit Valve can automatically cut off the regulating instrumentation and control valve the passage, so that the opening degree of valve ensure parked in front of location before it is broken, enable normal operation of process. Gas source failure eliminated, but also automatically resume normal work. the valve can be used as the safety protection device of automatic circuit