I just bought a house and inherited a troublesome STA-RITE cristal-flo (side mount) sand filter. After the initial problem of sand blowing out returns and blocking the return lines, I suspected a broken lateral; however, upon opening the filter, I found the sand bed had funneled down to where the inlet pipe enters the lateral assembly hub where they had blown apart. Obviously, this was allowing sand to escape in mass.
After digging out all the sand and removing the lateral assembly, I tested the fit of pipe and hub. The hub fits very loosely over the end of the pipe. In fact, it fits so loosely that it will fall off the end of the pipe if not supported from underneath. Is this right? I can't imagine that such a fit would stay together under pressure during a backwash. Is it supposed to be just friction fit or should there be a threaded fitting there?
To make it clear, the outlet pipe I'm talking about is a piece of grey flex pipe that goes into a PVC elbow and is connected to a short length of rigid PVC. It's this rigid piece that joins to the lateral hub.