Water pump questions

[cp1977]

My water pump seems to be misbehaving. Last year it always worked fine, pressured up quickly and shut down when taps closed. This year it runs constantly. I tested it and it appeared to be a slight airleak on the suction side. I replaced my inlet line and it worked better for a cycle or two. Then back to constant running. When running, it pumps water but at a reduced flow rate. Another peculiar thing is that when i turn the pump off, I can hear air leaking and the water in the inlet line leaks back down into the freshwater tank, emptying the suction line. Should there be a check valve in the pump? I am not sure what kind of pump it is but you can see the pump arm going up and down when it is operating. When I look at other RV water pumps, this arm does not appear to be visible. My pump also has the inlet and outlet fitting on the same side of the housing. The pump may be OEM in my 1977 Safari Land Yacht. Any suggestions? TIA Lorry

[NevadaGeo]

You might need to redo the diaphragm. I make my replacements out of a thick rubber roof material, about like inner tube. Get the old one out, use it for pattern, make the proper holes in it and put it back together. My pump has a couple hidden bolts that are a little difficult to find. A .38 and .22 shell works quite well to cut the holes.