Watts LF530C-3/4 Lead Free Calibrated Pressure Relief Valves 3/4-Inch Adjustable. Series 530C Calibrated Pressure Relief Valves are used in commercial, residential and industrial applications to protect against excessive pressure in systems containing water, oil, or air. It consists of a bronze body construction with NPT threaded male inlet and NPT threaded female (drain) outlet connections, stainless steel spring, brass bonnet, Buna-N disc, and Buna-N O-ring. Series 530C has a calibrated adjustment feature for setting the valve to the required relief pressure, and is ideal for by-pass thermal expansion pressure relief (not ASME approved). Model 530FP is for use in fire protection systems.