Valve apparatus

摘要

A valve device for controlling the operation of a safety valve in a flowline responsive to a pressure sensing pilot valve activated by a predetermined high and/or low pressure. Each form of the device disclosed has a body provided with a first chamber having an exhaust port and a safety valve control fluid port, a second chamber communicating with a control fluid supply port, and a third chamber communicating with a third port which is a control fluid supply port to a pilot valve in one form and an exhaust port in another form. A valve seat and flow passage is provided between the first and second chambers. A valve stem is movably disposed in the housing provided with a valve member in the first chamber for closing the exhaust port at a first position and for opening the exhaust port while engaging the valve seat closing the passage between the first and second chambers at a second position. A pressure-responsive piston is provided on the stem dividing the second and third chambers for moving the stem from the first to the second position in response to a reduced pressure transmitted through the port to the third chamber. The first and third chambers communicate through a passage including flow rate restriction means. One alternate form of the device includes a fourth chamber and another piston for using the device with a pilot valve operated by a pressure source independent of the control fluid source to the safety valve. Another form of the device includes additional passage means and a second piston in the third chamber for resetting the valve device after it has operated to close the safety valve.