Dear members,
I am currently sizing a rupture disk that can relieve both pressure and vacuum (Continental CAL-VAC type). The pressure setting is set as the design pressure of vessel which is 3.5 barg (50 psig). The vessel is also designed for a vacuum pressure of -0.7 barg.
The vacuum scenario could occur supposing that the vessel (normally vented to the atmosphere) and is 90% full of water, is isolated (V-1, V-3, V-6 are closed) and only the bottom outlet to a pump is open (V-2 is open). The pump is operates normally at 14 m3/hr, with TDH 50 m W.C.
My initial estimate to determine the gas space pressure is to use the ideal gas law based on isothermal conditions prevailing, i.e.:
P1 * V1 = P2 * V2 => P2 (final gas space pressure) = V1/V2 * P1 = 0.1*Vtank / 1*Vtank * (14.7 psia) = 1.47 psia
However, I was told by my senior that one could use the pump motor power / differential head to determine the maximum vacuum formed. But I have no idea how this could be carried out, or if this suggestion is correct in the first place.
I would like to see your advice on how best to approach this issue of estimating the maximum vacuum formed.
Thank you.