The Pressure Relief Valve: Increasing Safety in the Water System

Plumbing valves are used as fluid control devices which are usually located in a piping system at points other than outlets. Without them, water and other fluids would run freely through the pipes at all times with no way to shut them off for maintenance or any other reason. One very important plumbing valve is the pressure relief valve.

Water is a liquid that cannot be compressed. When water is in an enclosed piping system, if the pressure increases beyond the designed pressure of the plumbing system, a failure of the system can occur, causing leaks and water damage, leading to a potentially dangerous situation. That’s where the need for a pressure relief valve comes in. The pressure relief valve is a safety valve designed to open at a preset pressure level and relieve the system when it has exceeded the maximum rated level. The purpose of a pressure relief valve is to alleviate water pressure in order to prevent damage to the system. Common applications include water heaters, pumps, and water and well tanks. Below are the components that make up a (spring-loaded) pressure relief valve and how they contribute to the valve’s functionality:


A conventional spring-loaded pressure relief valve works based on the balance of force. The spring load is preset to equal the force that the inlet water applies on the closed seat packing when the system pressure is at the set pressure of the valve. The seat packing remains seated in the closed position when the inlet pressure is below the set pressure. The seat packing starts opening when the inlet pressure exceeds the set pressure, overcoming the spring force. At this time, the water would run out of the external drain (or outlet). The valve recloses when the inlet pressure is reduced to a level below the set pressure. To put a visual to this process, take a look at the graphic below.

A.Y. McDonald pressure relief valves include the 72049, 72048, and 6214 series. Each is no-lead material and comes in multiple size ranges. To learn more about pressure relief valves and our own product options, take the ‘Pressure Relief Valves’ A.Y. McDonald University (AYU) course, call our customer service department at 1-800-292-2737, or fill out a contact us form.