When valve operating torque creeps up, the first suspect is usually an undersized actuator. But if the torque trace steps up at one particular angle, or the problem disappears with a different fixture, the cause is more likely assembly or test boundary conditions than the actuator.
Read the curve before drawing a conclusion
- Confirm the fixture is not loading the stem sideways. Clamping offset adds side load, packing friction rises with it, and the reading can double. Align the fixture before discussing numbers.
- Separate breakaway, running and shut-off torque. Actuator sizing needs the maximum; life assessment needs the whole trace. They are two different questions and one peak answers neither properly.
- Record disc position, speed, medium pressure and temperature. Torque rising as the seat loads up is normal, but it should follow a consistent pattern. Testing under pressure and testing dry are different conditions and the report should say which one it was.
- Run a no-load check and a reference part to rule out torque transducer zero, coupling misalignment and drive backlash.
Sampling matters as much as the curve. Too coarse an angular interval hides the angle at which sticking starts, and unstable speed makes two runs impossible to overlay. Fix the speed, fix the sampling density, and run the same valve twice to check repeatability. Repeatable but uniformly high points to fixture and assembly; non-repeatable points to transducer and drive train.
When torque measurement needs its own module
If the product involves electric actuator sizing, handwheel operating force limits, life cycling or high and low temperature conditions, a pressure bench cannot substitute for torque acquisition. The specification should state range, accuracy, speed, angular resolution and cycle count, and the curve plus the verdict should be archived together.
In life cycling, torque is the primary observation: how far it drifts after thousands of cycles, and whether it steps at any point, reflects seat wear and packing degradation directly. How such tests are judged and how often they are sampled is covered in the valve life test FAQ, and torque traces and pressure traces are separate acquisition channels – the difference in how each is acquired and judged is explained in reading a pressure test curve. On the configuration side, how torque and pressure modules combine and how much headroom to leave in transducer range is set out in the equipment selection guide.
Bring two or three representative samples and the existing process parameters to a selection discussion and the proposal converges much faster.
Related test equipment
Each test above maps to a bench. Pick by valve type and by the item you need to prove:
- Valve torque test machine — break-to-open and seating torque curves for actuator sizing
- Valve life-cycle test bench — pressurised cycling with automatic counting and stop-on-failure
- Valve testing equipment range — browse all models by valve type and test item