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[robbiejustice]

I have an existing water tank operating at atmospheric pressure which will be filled automatically via an on-off valve on level control. The tank feeds 3 users via a centrifugal pump. The pump is always on recirculating water. The recirculation route back to the tank is after all the other users and has a manual valve on the inlet to the tank (not locked open on it). The tank has a lower design pressure of -0.9 barg and a vent with a hydrophobic filter which blocks on contact with water.

 

A control failure could cause the vessel to overfill and block the filter. The vessel could then be emptied by the users and the control system fail to open the fill valve to the tank. This is the only vacuum relief case but sensibly I cannot see a pressure below -0.9 barg ever being achieved as the vent filter would probably still pass something and the pump would probably cavitate and fail before this very low pressure was achieved. However, I am struggling to quantify this so as a conservative approach I am going to provide vacuum relief but it seems over the top.

 

Does anyone have a view on this?