Patent ID: 7823604

Claim:
An exhaust apparatus pressure control system comprising: a main body wherein an intake port and a discharge port are formed, the main body comprising a pilot chamber; a spool comprising an upper slide and a lower slide, the spool is attached by a spring to the upper part of the main body, and the spool is held by the upper slide and the lower slide so that it can slide in an axial direction over a sliding surface connecting the intake port and the discharge port; and an absolute pressure sensor for detecting the pressure in the intake port and a differential pressure sensor for detecting the difference between the pressure in the intake port and atmospheric pressure; a control valve for supplying a pressure regulating gas to the pilot chamber; and a control circuit for sending switching signals to the absolute pressure sensor and the differential pressure sensor, and driving the control valve based on the output from the absolute pressure sensor or differential pressure sensor; wherein a portion of the pressure regulating gas supplied to the pilot chamber is made a purge gas for protecting the absolute pressure sensor and the differential pressure sensor; a purge gas flow path connects the pilot chamber, the absolute pressure sensor and differential pressure sensor, and the intake port.