Inlet Strainers - Tech Talk 110
Pump inlets can become quickly clogged by just a few leaves, a plastic bag, a small amount of debris, or even a dead fish. Inlet strainers are devices that keep debris out of a pump that might otherwise damage or clog it. They generally are not designed to be water filters (requiring frequent cleaning), but rather pump protectors. A pump’s performance is greatly diminished when its inlet is restricted. To avoid flow reduction or stoppage, you will need an inlet strainer with a large enough surface area to not impede water flow, even when partially clogged.
Another reason you need a large surface area strainer is to reduce the water velocity at the strainer inlets, so that debris, small fish and animals do not become stuck. To prevent this, we recommend that the strainer screen surface area be a minimum of one square foot for every ten gallons per minute pumped.
The strainer opening should be small enough to keep out anything that will clog the pump, the pump’s strainer, and the orifices of any valves, etc. after the pump. Your water filtering device, if any, such as sand filters, bead filters, cartridge filters, etc. should be located just after the pump.
Stringy materials can be a problem because they can go through small strainer openings and wrap themselves on the pump’s impeller. To prevent this, use a very large surface area with a strainer inlet that creates a tortuous path. Spun polypropylene, open cell foam, and even multiple wraps of window screen over a strainer can be used for this purpose.
A check valve (also known as a foot valve) can be attached to the inlet strainer in applications where the pump will lose its prime when shut off. The check valve’s orientation is important for rapid and positive closure.