Dear sirs,
When a pressure drop higher than 3 % is reached at the inlet of a PSV, it migh cause chattering; Chattering is a cause of instability of the flow to be relief, and might cause also damages in the seat of the PSV.
But, appart from this, API 520 part II mention that chattering also migh cause lower capacity of the PSV.; Could you please explain why ? I mean, I understand chattering as a cause of inestability of the flow, but actually I do not understand how this directly recrease the PSV capacity...If I consider that the inlet pressure of the PSV remains constant , higher delta P at the inlet pipe would cause higher pressure in the protected vessel, but the inlet pressure of the PSV ( better said, relieving pressure would remain the same), so at the end, no matter the inestability, the rated flow thourgh the orifice of the PSV woudl be the same or not...?
thanks