Diatomaceous earth type pool filters require that the earth material be replaced when the filter becomes dirty through continuous use. To determine when the filter material should be replaced, it has been the practice to provide an indication of the inlet pressure to the filter. Dirt removed from the water gradually clogs the pores of the diatomaceous earth thereby increasing the back pressure on the pump.
It has been the practice in the past to provide a conventional Bourdon type pressure gauge which is connected to the top of the filter housing on the inlet side of the filter. Associated with the coupling gauge is a stop cock or valve for bleeding off air which may become trapped in the top of the filter housing. The combination of the valve, pressure gauge, and coupling to the top of the filter, which conventionally are made of brass, add a substantial cost to the pool filter installation.