Safety valves and Partial Stroke Actuators

2006-12-19T09:30:00.000-08:00

The industrial world is ever more concerned that a safety valve will operate should an emergency occur. There are too many examples of safety valves that have become frozen in place and inoperable for this situation to be ignored.

To assure valve operability, many users have applied partial stroke actuators that enable periodic exercise of safety related valves over a small portion of their travel. By moving the valve, if only a small amount, the user avoids disruption of the process while assuring that the valve has not become frozen and inoperable. Actuators that are sized to fully stroke the valve are able, when called upon, to limit the valve travel to a pre-defined portion of the total stroke for test and exercise. Subsequently, these actuators will again impart full travel to the valve.

Partial actuator stroke can be achieved by use of intelligent positioners that are programmed accordingly or actuators that are purposely modified to, upon demand, provide only a portion of their normal travel.

Some actuator designs employ locally installed pins or other mechanical means to temporarily limit the actuator travel. Users would install the pin locally, then operate the actuator either locally or from the control room, removing the pin when the testing is completed. A problem arises however in that the actuator location may make access difficult, or worse, pin removal may not occur, leaving the actuator incapable of full travel. We have a better solution.

As many are aware, QTRCO has successfully applied tandem piston actuators for use by customers who have lower than normal supply pressures. Using the same technology, we are able to incorporate a tandem piston as a remotely engageable travel stop to temporarily limit travel of the primary pistons. This means that an operator can enable partial stroke testing without leaving the control room, perform partial stroke testing as desired and then confirm that the tandem piston is dis-enengaged to allow full valve travel.

Summary; our design works well for both throttling and on-off services (where positioners are otherwise not needed) while enhancing convenience, allowing numerous exercise cycles and providing assurance that no travel limitation exists following the testing. Added to the already exceptional performance of the QTRCO actuator, we think we have a winning design.

We would appreciate an oportunity to describe our capabilities in greater detail.

Ed's Blog

Safety valves and Partial Stroke Actuators