as long as I know, the tests in object are typically applicable to control valves, especially when (smart) positioners are present. Maybe You'll want to refer to IEC 60534 standard, Part 1 (July 2005) and Part 4 (June 2006) for definitions and/or to Shell DEP 32.36.01.17-Gen specification (just to make an example) for more information. Notwithstanding our objections, one Customer insisted to have this kind of tests done on on-off valves, operated by means of electric motors and gear reducers (!). Is this just a persevering error, or are there any actual reasons to investigate what happens to the valve obturator far from the fully closed position?If the answer is yes, he should know it does not make sense to consider this parameter for an on/off valve. Otherwise he knows the definition but does not understand it.You could show him a diagram which illustrates the meaning of hysteresis, applied to a proportional control valve, that is in a case where it is meaningful to talk about hysteresis. Then explain him that it takes a complete cycle for the valve to establish the max difference (as measured along a horizontal line) between the characteristic valve curves with increasing and decreasing input.For an ON/OFF the valve has just two positions of interest (fully open or fully closed). What to do with an hysteresis value that, no doubt, occurs for an intermediate position of the stem?

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