I have in my house installed a water mist fire protection system. Currently it is connected directly to the main water system, which is of lower pressure than the nozzles are designed for.
I would like to add a pump and an expansion/pressure tank to increase the pressure.
My question is what kind of water pump can I use for this? It is an absolutely requirement that it will not significantly reduce the pressure or amount of water flowing through it in case of missing electricity. How well will centrifugal pumps let water flow through without power?
A battery backed solution that turns on/off a bypass path in case of power loss might be acceptable, but my initial thought is that this is added complexity and something that could fail so I think I would prefer not to have that.
Since the normal use case will be that the pump starts once to fill the tank and then never start again, power consumption and efficiency are of no relevance.
Best Answer
A simple solution would be to install a full sized bypass with a check valve, which ties in downstream of the pressure tank. This would allow full system flow in the case of pump failure. You could then use a pump of whatever type fits your needs most efficiently and effectively, and would need not be concerned about flow restriction through the pump.
You do not mention the nozzle activation mechanism but we must assume that the heads are closed unless opened due to fire melting a fusible/frangible element at the head(s) or other mechanical means. So... under static conditions the system would remain at the pressure held by the tank diaphragm, which would be above mains pressure (because it was pumped). Upon opening/activation of a spray nozzle then the tank would deliver until pressure drops enough for mains pressure to then lift the check valve and flow into the system, around the pump and tank assembly.
sorry for crude drawing of bypass with check valve