Abstract: A shut-off valve in a fluid line closes by spring pressure and incorporates a control chamber wherein pressurized control fluid acting on a piston opens the valve in opposition to the spring pressure. A control system for the shut-off valve comprises a 3-way actuator pilot of the present invention in cooperation with a monitor pilot. The actuator pilot has a valve spool and four ports, namely, a supply port connected to a source of pressurized control fluid, a pilot port connected to the monitor pilot, a control port connected to the control cylinder of the shut-off valve, and an exhaust port for venting the control chamber of the shut-off valve. When the control system is in service and the monitor pilot senses an undue change in the pressure in the fluid line, the monitor pilot vents the actuator pilot to shift the valve spool therein to cut off the control fluid from the control port and simultaneously to place the control port in communication with the exhaust port to cause the shut-off valve to close.

Abstract: A shut-off valve in a fluid line closes by spring pressure and/or line pressure and incorporates a control chamber wherein pressurized control fluid acting on a piston opens the valve in opposition to the spring pressure and/or line pressure. A 3-way actuator pilot normally places the control fluid in communication with the control cylinder but when vented cuts off the control supply fluid and releases the pressurized control fluid from the control chamber to cause the shut-off valve to close by spring pressure and/or line pressure. A monitor pilot responsive to pressure changes in the fluid line incorporates a relief valve and opens the relief valve by cam action to vent the actuator pilot whenever the pressure in the fluid line makes a predetermined departure from a normal pressure range.

Abstract: Pressurized fluid is controlled by a reverse valve gate on a valve stem that extends through annular packing in a bore of a bonnet to a piston in an outer control chamber. Control fluid pressure moves the piston inward to open the valve against line pressure on the valve and/or spring pressure on the valve. In the absence of both line pressure and control pressure, the valve is closed by spring pressure. The control chamber construction permits quick replacement of control chamber seals. In the event of a fire, the control chamber seals disintegrate to release the control pressure and thus cause line pressure and/or spring pressure to close the valve. The valve stem packing may be conveniently expelled hydraulically for replacement. Various different control assemblies may be mounted interchangeably on the valve bonnet without disturbing the structure of the valve. An auxiliary control may be quickly mounted on the outer end of the control chamber to convert the shut-off valve to manual operation.