For linear control valves that require a specific seat load to ensure shutoff, Xpac Linear Series Actuators can be equipped with an elastic coupling. The elastic coupling is comprised of pre-compressed Belleville washers and sits between the valve and actuator stems. As the valve plug engages with the seat, the washers compress and the indicator pin slides into position. The dual purpose of the elastic coupling is to indicate positive seat load and compensate for thermal expansion of the valve stem or seat.
Seat Load Cylinder
A seat load cylinder (SLC) is used on actuator systems that are too large for elastic couplings. The SLC is a spring opposed cylinder hydraulically connected to the actuator cylinder. When the actuator cylinder reaches a hard stop (valve seat), pressure builds in the SLC. The pressure compresses the spring until the SLC reaches the calibrated seated position. An externally viewable indicator provides visual confirmation that the valve is seated.