Patent ID: 7445163

Claim:
A suck back valve comprising: a joint section which has a fluid passage and which includes a first port formed at one end and a second port formed at the other end; an ON/OFF valve which opens and closes said fluid passage by means of a valve plug displaceable in accordance with a pilot pressure; a suck back mechanism which includes a displacement member displaceable in accordance with a pilot pressure, a flexible member connected to said displacement member to make displacement integrally, and an elastic member fastened to said displacement member and which sucks a pressure fluid contained in said fluid passage under a negative pressure action of said flexible member; a load-detecting mechanism which detects a load applied by a resilient force of said elastic member corresponding to a pressure of said pilot pressure to be supplied; and a control mechanism which detects loads before and after displacement of said flexible member by using said load-detecting mechanism to calculate a displacement amount of said flexible member based on a difference between said detected loads, wherein said load-detecting mechanism comprises a load sensor which converts said applied load into an electric signal, and said elastic member is composed of a spring member which has one end fastened to said displacement member and another end fastened to said load sensor.