Safety Interlock to Open SCSSV First

The SCSSV must have a safety interlock to make sure that this valve is opened before the SSV. The SCSSV is extremely difficult to open when there is a maximum differential pressure across the valve, which would be true if the SSV were opened first.

The addition of a pilot relay in the pneumatic circuit is the method usually used to provide the safety interlock. Pressure is thereby supplied to the hydraulic pump supply pressure, the hydraulic dump valve, and the supply port of the manual reset pilot relay that controls the SSV.

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