Strainers for Backflow Prevention Device Assemblies – Installations

Strainers are designed to permit removal of the filter for replacement and repair without removing the body from the line. The strainers shall be flush out and cleaned periodically. A clogged strainer will create a pressure loss and is some cases will cause the flow of water to cease. The strainer filter shall withstand 125 psi when plugged. Friction loss shall not exceed 10 psi when tested with foreign materials is trapped in the strainer. Friction loss shall not exceed 3 psi at rated flow when tested with clean filter and clean water. Consult manufacture literature for information regarding specifications.

Strainers installed on fire protection system prior to the backflow prevention device assembly may utilize a water spray system to prevent the clogging of the strainer. Strainers for fire systems are designed to trap foreign material 1/4″ diameter or larger. This type of strainer is usually installed upstream of the backflow prevention device assembly and flow alarms, to prevent damage or check valve fouling.

Because strainers along with the backflow prevention device or assembly will reduce the pressure being delivered to the end use or last free flowing tap, pressure loss calculation should be completed prior to the installing them on service lines because the pressure loss generated by the installation may create a health hazard. Strainers along with backflow prevention device or assemblies should only be used if absolutely necessary.