Partial Stroke Testing (PST) stands as a fundamental practice ensuring the reliability and safety of valve monitoring and control systems. This method involves precisely maneuvering a valve to a predetermined position within its operational range, typically a fraction of its full stroke, enabling the examination of critical components such as the valve, actuator, and solenoid valve while maintaining operational safety.
One of the primary advantages of PST lies in its capability to evaluate the functionality of the entire valve system seamlessly, without disrupting its regular operation. By conducting partial strokes at regular intervals, operators can validate the accuracy and dependability of the valve’s output signals while it remains in service. This proactive testing approach aids in early detection of potential issues or deviations in valve positioning before they escalate, thereby bolstering the overall safety and performance of the system.
For safety valves designated for emergency shutdown, periodic testing is imperative to uphold their functionality and Safety Integrity Level (SIL) rating. PST emerges as a cost-effective solution, allowing partial closure of the valve without interrupting ongoing processes.
While PST does not replace mandatory full stroke tests necessitating plant shutdowns, it effectively prolongs the interval between Full Stroke Tests (FST), resulting in enhanced production output and cost efficiencies. Intelligent PST plays a crucial role in distinguishing between “safe failures” requiring scheduled maintenance and “dangerous failures” demanding immediate attention.
The Digital EPIC D500 from Westlock Controls represents a cutting-edge, second-generation transmitter-based intelligent device, boasting advanced diagnostic capabilities, including PST. During PST operations, the valve undergoes controlled movement to a preset travel limit within a configured timeframe before returning to its original position. Moreover, the D500 captures and stores PST signatures, utilizing the valve signature established during commissioning as a benchmark for future comparisons. Any deviation beyond a preset hysteresis limit prompts an alarm, facilitating the prompt identification and resolution of potential issues.
