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Velocity Check Valves : Product Details

Velocity Check Valves are two position, two way Normally Closed, positive flow shut-off, manual reset, flow control safety devices. They are also commonly referred to as "Excess Flow" or "Surge Check Valves". Our Velocity Check Valves are designed to provide instantaneous, positive flow shut-off in the event either of the following abnormal process conditions occur: (1) an abrupt, high pressure surge develops at the valve's inlet connection, (2) a significant pressure differential develops downstream of the valve's Outlet connection or in the receiving control circuit.

There are three basic, control circuit applications that typically utilize Velocity Check Valves. In all applications, the Velocity Check Valve is installed at or near the monitored media process connection or instrument pressure source. Velocity Check Valves first pressurize the receiving control circuit or device (through manual operation), and thereafter react to the development of a pressure differential by instantly, blocking internal flow. Typical control applications are listed next.

1. As a Rupture Response flow control valve.

Rupture, due to over pressuring, could occur to any control that utilize Diaphragms, Bourdon Tubes or Helical Coil components. Once the pressure sensor mechanism ruptures, the Velocity Check Valve would provide positive flow shut-off to prevent the discharge of fugitive emissions, by instantly stopping internal flow at its Inlet connection.

2. A "Push-To-Charge" (Pressurize) Safety System Control Circuit.

The Velocity Check Valve is generally employed in an Emergency Shutdown (ESD Safety System), control circuit for this application. It is first used to pressurize the receiving control circuit, by manually pushing inward on the Knob. Thereafter, the Velocity Check Valve will provide both orifice flow and then positive flow shut-off, in response to the initiation of an Emergency Shutdown. The Velocity Check Valve's orifice (restricted flow configuration) compensates for minor leaks and also maintains constant operating pressure in a closed loop control circuit (that normally experiences pressure changes due to temperature fluctuations, etc.).

Actuation of the ESD Valve or some other critical function, monitoring control device, will create a pressure differential within the receiving (downstream) control circuit. The operating instrument supply pressure would be isolated or sealed at the Velocity Check Valve's inlet (to prevent continuous flow). A Shut-In or critical Safety Valve (SDV or SSV) closure occurs, as the ESD (downstream) circuit becomes depressurized. ESD Safety Systems normally use Nitrogen, Hydraulic Fluid or Natural Gas as the operating instrument supply media or operating pressure source.

3. To pressurize and operate Line Pressure Operated - Safety Systems.

Line Pressure Operated (LPO) Safety Systems are self-contained, surfaced mounted, Safety Valve components that respond to either abnormal high or low flowline pressure. Pressure monitoring devices (Pressure Sensors or Actuator Pilots) are installed to provide the "Shut-In" (Safety Valve closure) response, by isolating and depressurizing instrument supply (operating control pressure) to the Safety Valve. The Velocity Check Valve is used to first pressurize the Safety Valve's actuator assembly and then the Pressure Sensors for normal, operation. Once component and control circuit pressurization is complete, the Pressure Sensors will thereafter, detect and react to an abnormal, monitored pressure deviation. One of the Sensors will be actuated to exhaust all accumulated instrument supply pressure. A pressure differential is then created within the closed loop, control circuit through the Velocity Check Valve. The Velocity Check Valve will isolate the instrument supply pressure at its source. All operating instrument supply pressure previously accumulated, will be exhausted from the safety system to provide Safety Valve closure (Shut-In). The Velocity Check Valve will also provide the "lock-out" or manual reset (fault acknowledgment) feature necessary for "failsafe" (fail closed), safety system operation.