Which is better, flow sensor before or after flow control valve? Flow sensor mounted horizontal or vertical? My thinking is if you need low flow lets say to a fuge, would it be better to have a flow sensor before a flow control valve allowing water to completely fill the pcv pipe and flow sensor? If you mount the flow sensor horizontally and put the flow sensor after the flow control valve the flow sensor may not be completely full of water. Would this give you inaccurate flow readings? I understand that if you mount the flow sensor vertically with flow in the upward direction it should not matter. Which mounting is preferred? Any recommendations would be appreciated.