Every steam and hot water heating boiler must have at least one safety or safety relief valve of sufficient relieving capacity to meet or exceed the maximum pressure output. Often considered the primary safety feature on a boiler, the safety valve should really be thought of as the last line of defense. If something goes wrong, the safety valve is designed to relieve all the pressure that can be generated within the boiler.
The safety valve must be set to open at or below the maximum allowable working pressure established by the manufacturer. This is the maximum pressure at which the designers have determined the boiler can be safely operated. The maximum allowable working pressure is usually listed on the boiler nameplate or stamping located on the side of the boiler.
The ability of a safety valve to perform its intended function can be affected by several things, such as internal corrosion or restricted flow, which can prevent the valve from functioning as designed. Internal corrosion is probably the most common cause of the malfunctioning of safety/relief valves. This condition is generally caused by slight leaking due to improper installation of the safety valve and is a condition that should be corrected without delay.
To ensure that a valve’s mechanism will operate properly, the try-lever should be lifted once a month and the valve set pressure tested annually. If a valve will not operate or does not reseat properly when tested, the boiler must be shut down immediately and the valve repaired or replaced.
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