I have a NS Oscar that is a direct water connection model. I am going to fit an OPV and my thinking is that if the relief line from the OPV is rerouted back to the pump inlet, that the inlet side of the pump will be pressurized above the 1.5 bar supply pressure. Is this correct? I will probably just let the relief pressure go to the drain tray, but I am curious if what I think will happen in theory will happen in practice.

Baz

No, the pump would be taking more fluid of the inlet side than the opv was putting back in, the pressure the opv is opening at is not what determines a rise in pressure at the opv outlet/pump inlet. Its all about the volume flow rate and system volume, which is low and high respectively here.

Would this be true in a situation where there is a total by pass, such as a blind filter?

The sum flow rate out and in at the inlet side of the pump would be zero, so nothing much happening