Fail Safe Operation of Big SVC Stargate O-Port® valves in Combination with Electronic Positioner

The drawing is indicating two Stargate O-Port® valves with the tandem actuators, the accumulator, the solenoids, the accumulator, the pressure switch, and a check valve. The one SVC Stargate O-Port® valve at the bottom is shown in the fail-open, the other one at the top in the fail-closed position.

“P” indicates the connection to the compressed air system.

Check valve C1 prevents the pressure in the accumulator to go back to the air supply system.

The accumulator has a plug in the bottom to release water from the accumulator. It will be necessary to open this plug infrequently because only make up air for air leakage and usage of the fail open/close system brings humidity into the accumulator.

SV1 is a piloted single-coil solenoid valve with a normally closed position, SV2 is a single-coil solenoid valve with a normally closed position, and SV3 is a single-coil solenoid valve with a normally open position.

When the plant starts operation SV3 is energized and goes into the closed position. SV1 and SV2 are controlled by the Allen Bradley Micrologix 1000 PLCs. The PLCs compare the 4-20 mA signal from sensors on the valves with a demand signal of 4-20 mA from a DCS control panel. These sensors are ultrasonic or magneto-strictive.  Depending on a positive or negative difference between the demand signal and the signal from the sensors, either SV1 or SV2 is energized. When the required position of the Stargate O-Port® valve blade is reached the energized solenoid valve goes to the normally closed position, the blade motion stops. The exhaust air from SV2 goes out of port E directly into air. The exhaust air from SV1 goes into port A of SV3 and out through port E of the energized SV3.

SV3 is energized while the plant is in operation separating the accumulator from the actuators. In case of a power failure and/or a reduction of air pressure below a certain pre-set pressure SV3 is de-energized, which brings the pressure in the accumulator through ports P and A of SV3 and E and A of SV1 to the actuators extending the rods and opening the Stargate O-Port® valve (bottom valve), respectively retracting the rods and closing the Stargate O-Port® valve (top valve). The piloted SV1 allows pressure to enter through the exhaust port E.