This means that, on loss of signal, the valve positioning unit will freeze the valve in the last known position based upon the pneumatic signal at the time of failure. Normally, on losing the signal air, the valve would open or close fully depending on the pneumatic positioner's setting.
However, in some situations, it's important to keep the process running at some level until the batch or system can be shutdown and checked out. This is where fail-freeze comes in handy.
RENCOR recently designed and built an automated 2" ball valve package with a fail-freeze pneumatic positioner, regulator, and pilot valve combination that assured the valve would stay put when the 3-15 psi signal air was lost.
A manual override was included that allowed for manual control of the valve during the batch process and for a controlled shut down after the batch was complete.
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