Strainers for Backflow Prevention Device Assemblies – General Specifications

Strainers are installed on the inlet side of backflow prevention devices or assemblies to prevent rust, dirt, rust and other damaging debris from the inlet water service line or public water distribution system from entering the backflow prevention devices and assemblies. Backflow prevention device and assemblies are designed to prevent backflow by controlling the reversal of flow in a piping system. This is accomplished by the use of check valves that close drip tight when the backflow occurs. Over time, dirt or debris can get lodged between the check valve and check valve seat creating a situation where the check valve will not close drip tight. The dirt or debris over time could render the check valve disk to become damage and not seat properly. Debris accumulation on the first check valve seat is one of the prime factors associated with first check valve failures. Backflow prevention devices or assemblies with damaged or fouled check vales are compromising the effectiveness of the backflow prevention devices or assemblies to provide the appropriate cross-connection protection to the potable water system.

The strainer is a device that mechanically removes solids from flowing fluids. This is accomplished by utilizing a perforated metal, mesh or wedges wire straining element. The most common range of strainer particle retention is 1 to 40 micron. By installing a strainer upstream of backflow prevention device or assembly, the mesh filter in the strainer will catch debris before entering the backflow prevention device or assembly.There are two types of strainers used in connection with backflow prevention devices or assemblies, the wye strainers and basket strainers. The strainers come in a variety of sizes, shapes and material. The wye strainer can be installed vertically or horizontally provided that the wye strainer installed vertically is placed with the screen in the downward position to trap the sediment in the debris collection chamber. The basket strainers shall be installed in a horizontal position only.