Pressure Relief Valve (PRV) is a system safety device that has been designed to function in accordance with specific country codes to prevent and protect the operation of systems and vessels above allowable safe levels.
Pressure Relief Valve conform to the American Standard Safety Code for Mechanical Refrigeration (ANSI/ASHRAE 15), and are designed and manufactured in accordance with ASME Section VIII Division 1, certifying specific capacities and identified by the ASME and National Board NB stamps on each valve. These Pressure Relief Valve are also compliant with European Union Pressure Equipment Directive (PED 97/23/EC), and exhibit the appropriate EC marking and identification number.
Pressure Relief Valve operate automatically when the system pressure exceeds the valve set pressure and exerts a force on the valve disc that overcomes the opposing internal spring force. By code, valves may open with allowable tolerances within a +/- 3% range of stamped set pressure, with full discharge capacity realized at 10% above the actual opening pressure.
Selection of a Pressure Relief Valve should be based on the discharge capacity required for the system or vessel, based on the size of the equipment and the refrigerant being used. Minimum settings for Pressure Relief Valve should be at least 25% above the designed Maximum Operating Pressure, while additional consideration must be given if the valve location may experience high ambient temperatures such as an equipment room or rooftop. Sizing valves to the maximum allowable setting will minimize the possibility of seepage or early discharge.
While Pressure Relief Valve are designed to reseat after discharge, it is advisable that they are replaced, since system impurities such as piping debris, solder, and metal shavings can accumulate under the valve disc and inhibit the proper resealing of the valve.