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Pressure Vessel Testing

Pressure Vessel Testing

Pressure Vessel Testing

(OP)
Old Tester- diaphram pump, pressurizes 70 PSI / stroke then regens until vessel breaks.

New Tester- I designed a feed back loop analog control to regulate the pressure gradient at 80 - 100 PSI / Sec. Using a booster cyl., the pressure is gained linearly and adjusted 100 times a sec.
Both mediums are water.
Both sample lots used in the testers are from the same materila batch ( PolyPropelene ) from the same process, at the same manufacture time and from the same press.
Problem: The old tester breaks vessels at 700 PSI + -
The new tester breaks them at 500 PSI + - .
Could there be a stress re-allignment going on in the old test that is not present in the new, due to the rest between pulses. ( rest time is approx. .2 sec., Pulse is approx. .3 sec. ) which is allowing the vessel to fail at a higher pressure ?

Other factor - New uses threaded nipples and the old uses a air cylinder to clamp.

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