"Richard Smith" wrote in message ...
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For fatigue testing samples - it has to tension and release millions
of times.
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If you want simple, a 3-port rotary valve would alternately let oil in and
out of the cylinder. You could run it slowly until you determine how fast
you can spin it and still attain full and minimum pressure. The valve could
operate a revolution or cycle counter. If you can tolerate a little leakage
it's simple enough for a model engineer to make. ( I have too many machining
jobs for the sawmill and its gantry hoist in the queue to offer. )