Reduced Pressure Principle Backflow Prevention Device Assembly Relief Valve Drainage

Under no circumstances should plugging of the relief port be permitted because the device depends upon an open port for safe operation. Malfunctioning of one or both of the check valves or relief valve will be indicated by a discharge of water from the relief port.

Reduced Pressure Principle Backflow Prevention Device Assemblies (RPZ) may discharge large amounts of water and should be equipped with a suitable drainage system, especially if installed indoors. Discharge from relief valves must be readily detectable to maintenance personnel either visually or by means of water level alarms, flow indicator lights, or other suitable warning system. Manufacturer’s air gap fittings may be utilized provided that they maintain a proper air gap and do not enclose or cover the relief valve. These fittings are only sized to handle intermittent and low flow discharges they are not intended to handle a catastrophic discharge.

All drainage from RPZ’s must be by gravity drains. Sump pumps are not allowed unless they are sized to accommodate the maximum discharge rate and connected to emergency power supplies.

An air gap must be maintained between the RPZ relief valve opening and any discharge piping. The air gap must be at least twice the dimension of the effective opening of the relief valve; but in no case less than 1 inch.

Discharge piping from relief valves shall be terminated a minimum of one inch above any floor drain or other receiving receptacle.

Discharge piping connected to a storm sewer shall be equipped with backwater check valve.

Discharge piping connected to a sanitary sewer shall be trapped and equipped with a backwater check valve. Discharge piping from structures must be terminated above grade in an area not subject to flooding (generally one foot above the 100 year flood elevation). The terminal end of the discharge piping must have a rodent screen and may need to be supported by a headwall. Flap valves should also be considered to prevent entry of cold air and all exterior drains shall be kept free of snow during winter months.

Where a RPZ is installed out of doors, a concrete pad, or other suitable arrangement shall be provided to prevent erosion of the surrounding area.

A no drainage arrangement or piping system is not acceptable nor is it an approved installation.

Damage can occur to walls and structures if the appropriate drainage is not provided. Note the containers filed with water from the relief valve discharge. This was a new installation and after several days during the evening when there was no demand downstream, the relief started to discharge water continually. The cause was most likely a first check valve failure due to debris embedded on the check valve seat or disk. The debris was most likely coming from the public water system water supply. The RPZ was installed after the meter on the service line.