Diagnostic Partial Stroke Testing Mechanics in Gas Isolation Systems
Partial stroke testing isolates eighty-four percent of undetected mechanical failures in gas isolation valves by dynamic torque profiling without interrupting process flow.
Breakaway Torque
Meaning
The initial rotational force required to start the movement of a stationary valve or mechanism is known as the breakaway force. When calculating breakaway torque, engineers measure the peak force needed to overcome the static friction of internal seals and seats. This value is higher than the run torque needed to keep the valve in motion.
It governs the minimum output requirement for any pneumatic or electric actuator attached to the assembly. If the actuator cannot deliver this force, the valve remains stuck in its current position.
Frictional Resistance
Seals and seating materials determine the initial force needed to move the valve disk. Elastomeric seats tend to stick to the metal surfaces over time, especially during periods of inactivity. This sticking action increases the starting resistance.
Harder materials like Teflon or metal-to-metal seats require different calculations because they do not deform as much under line pressure.
Torque Margin
Actuators must be selected with a capacity that exceeds the initial movement requirements by a defined safety factor. In standard distribution agreements, manufacturers specify the start torque at maximum differential pressure. A safety margin of thirty percent is commonly applied to ensure reliable operation under varying line pressures.
This margin prevents operational failure when fluid viscosity increases or when deposits accumulate on the internal components.
Testing Verification
Factory tests verify these torque requirements before the assembly is shipped to the field. Technicians use a torque wrench or automated sensor to measure the force required to open the valve from a fully closed position. These values are recorded in the test certificates that accompany the shipment to the customer.