The Spence Type VH210 Pilot is intended for use with a Spence E or C Series Main Valve. This pilot/main valve configuration is designed to control a process variable in proportion to a continuous electronic signal received from a user supplied process controller.
The main valve is normally closed, held by an internal spring and initial pressure acting on its disc. The VH210 Pilot is controlled by the continuous proportional electronic signal received by the actuator from the process controller. When the process controller signals the VH210 Pilot to open, process fluid flows through the pilot to the main valve via the bends and fittings, actuating the main valve by causing pressure to build under the main valve diaphragm. Depending on the signal received by the process controller, the VH210 Pilot may be closed, partially open or fully open. Once the main valve opens, the downstream fluid variable is affected, measured and fed back to the pilot via a variable transmitter and the process controller.