The temperature switch on your water heater sticks, and the water begins to boil. The pressure skyrockets until the tank bursts in a massive explosion like a bomb tearing through your house. Without safety relief valves, this could easily be a true story.
Safety Relief Valves
A safety relief valve, or pressure relief valve, is a safety device installed on or near the top of any tank that contains a liquid that is at risk of pressure build-up from any heat source. They are designed to open and allow pressure to escape so that the tank will not explode, then close again once the pressure is below the danger point.
How They Work
A pipe nipple extends from the bottom of the pressure relief valve (PRV) and is screwed into the top of the tank. The body of the valve contains a tension spring and a flat disc, the spring holds the disc tightly against the end of the nipple. When pressure in the nipple is stronger than the preset spring pressure, the disc is forced upward, allowing pressure to escape from the nipple. Once pressure drops lower than the pressure exerted by the spring, the disc will again be pushed against the nipple, closing the PRV. Water heater PRV's also have a temperature sensor extending into the tank through the nipple, which can also open the valve if the temperature exceeds a pre-set danger level.
Other Common Uses
PRVs have many common applications. They are used on the hot water tank on furnaces in homes and other buildings with hot water heat, on the propane cylinder on your gas grill and on the propane tank in the neighbor's back yard. They also are used in nuclear power plants and on the nitrogen tanks farmers use. Every pressure tank that can experience a dangerous rise in pressure is required by law to have a PRV installed.
- Photo Credit Heizung image by nizo from Fotolia.com valve and pipe image by Daria Miroshnikova from Fotolia.com Steam Power Plant image by dvest from Fotolia.com
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