There is one item on all boilers, water heaters and pressure vessels that has been installed for the protection of people who are or may be in the vicinity of the equipment. This very important piece of equipment is the pressure relief valve (PRV) and is it installed to ensure the equipment doesn t fail catastrophically due to overpressure. These PRV s require testing on a regular basis (preferably monthly) to ensure that they will work when they are needed.

The testing of PRV s is a simple task, but the importance cannot be over stated. A simple procedure would be to first locate the PRV on the equipment; it will be on the top of the boiler or vessel, or side in the case of water heaters, or air receivers. These PRVs are valves with a lifting lever or device (rings, etc.) on the top side of the valve.

Following these precautions when testing PRV:

• Wear gloves and safety eye wear to ensure your protection.
• Stand to the side of the discharge pipe; don t stand in front of the valve discharge.
• Locate the inlet isolation valve and shut off switch for the equipment. This is a precaution in the event of a problem s arising from the PRV s failing during testing, to enable the person testing the PRV to shut off the equipment if required.
• Locate the testing/lifting lever or device on the top of the PRV.
• With system pressure at at least 75% of the PRV set pressure, gently lift the lever, while watching the outlet pipe for flow of the product from the vessel or boiler and continue to open the valve until fully opened. If the valve is very stiff or seized do not force it open, shut down the equipment and replace the valve with a new one of the applicable specification (see last bullet).
• Watch the flow out of the discharge piping. Allow the flow to continue until a clean stream is coming out of the discharge pipe. Then allow the valve, which is spring loaded, to snap shut. Watch the discharge pipe to be sure the flow stops. This may take a few minutes to drain all the fluid from the lines.
• If the flow doesn t stop completely, the procedure can be repeated again to see if the valve will re-seat properly.
• If the PSV will not open with the lifting lever, it requires changing Immediately, as it would not function when required and an explosion could occur with deadly results.
• If the PRV doesn t close properly and is leaking, it requires changing, but would probably work if it was required. A leaking PRV should be replaced as soon as possible.
• Ensure that the replacement valve is sized properly; this information will be on the boiler nameplate. The information to be noted is the MAWP (maximum allowable working pressure) usually stated in PSI (pounds per square inch); the new valve must have its set pressure at or lower than this pressure. The second piece of information is the minimum PRV relieving capacity; this may be in lb/hr (pounds per hour) or in BTU/hr and the new valve must have this rated capacity or higher to ensure safety.