The Truflo BRP Series Back Pressure/Relief Valve has two functions. As a back pressure valve installed in-line downstream of a pump. In this position the back pressure below the metering pump is maintained. When the PRB valve is installed in the branch of a tee fitting it functions as a pressure relief valve. The valve remains closed until inlet pressure reaches the preset pressure which is adjusted by turning the spring tensioning bolt. The pressure at the inlet of the valve acts upward against the piston allowing the liquid under higher pressure to flow upwards through the orifice.