Photograph of a water tank pressure relief valve Water Tank Pressure Relief Valves
     

  • WATER TANK PRESSURE RELIEF VALVE - CONTENTS: What are water tank pressure relief valves, where are they installed, why are they needed? Has anyone been injured due to failure to install a pressure relief valve on a water tank? Yes.
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Water Tank Pressure Relief Valves:

how to find buy, or where to install safety valves on water tanks and on well water systems. We explain where a pressure relief valve is usually installed on well water pressure tanks, how the valve works, and why pressure relief valves are an important safety feature on well tanks.

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WATER TANK PRESSURE RELIEF VALVES: installation, inspection, troubleshooting, repair, code requirements for

Photograph of a water pressure tank air valve

Safety warning: all pressurized tanks should have an appropriate pressure relief valve installed to avoid possible injury should the tank burst. In this photo the brass fitting to the right of the black tank drain is a pressure relief valve installed in the correct location.

Notice that there is no shutoff valve of any kind installed between the relief valve and the pressure tank?

If the pressure relief valve is leaking this is an UNSAFE condition (corrosion or mineral deposits could block the valve and prevent its operation in an emergency). The valve should be replaced.

Early in our building inspection career plumbers in our area were skeptical when we identified the absence of a pressure relief valve as a safety concern (and a building or plumbing code violation). Then in about 1984 a local plumber was killed by a bursting water pressure tank.

The water pump was a submersible unit located (remotely) inside of the water well. The plumber was leaning over the water tank repairing a fitting, unaware that the water pump had turned on, and unaware that the pressure control switch had been damaged or modified so that it failed to turn off the water pump at a safe pressure.

The water tank burst, metal fragments severely injured the plumber who, working alone, bled to death. After that terrible event all of our local plumbers took this relief valve requirement seriously.

How to Buy & Install the Right Water Tank Pressure Relief Valve for Water Storage Tanks or Water Pressure Tanks

Question: What size or capacity of pressure relief valve should be installed on a water pressure tank?

My water tank pressure switch is set to 20 - 40 psi. How do I gage the size of a relief valve I need to put for my tank? - D.R.

Reply: typical water tank pressure relief valves are 1/2" or 3/4" in diameter orifice and are set to open at 75 psi.

The water tank pressure relief valve shown in our photo (above) is marked indicating that it will open at water pressure equal to or greater than 75 psi. That pressure is pretty standard and you'll see the 75 psi figure on valves used on water tanks and on some tankless water heaters too.

According to the Water Systems Council, [quoting, paraphrasing, and expanding - Ed.]

High pressure in a building water supply system can result if the water pressure switch that controls the well pump is damaged, or if the pump stays on too long.

Most submersible well water pumps can develop pressure exceeding the rated working limits of the water pressure tank or building water distribution system piping, fittings, and fixtures. Excess water pressure can damage water system component as well as the pressure tank if not corrected immediately, and can also cause leaks within the piping system or at faucets and fixtures. Therefore on all building water supply systems using a private well and pump, a pressure-relief valve is recommended.

Water pressure relief valves are spring-controlled and open only in response to system pressure. That is, water temperature is not a controlling factor for these valves. For water service, these important safety devices are generally adjusted to relieve pressure higher than 75 psi. [1]

Watch out: water pressure tank fatality: we [Ed] are aware of a fatality that occurred in the Hudson Valley of New York State when a plumber, working alone on a water pressure tank and pump system was killed as the water pressure tank burst. There was no pressure relief valve on the water system; a submersible well pump was installed; the well pump pressure control switch stuck in the "on" position.

We suspect that because the submersible pump was located inside the well and thus there was little or no operating noise when the pump was on, the plumber had no idea that the pump was running. When the pressure inside the water tank exceeded the tank's design specifications the tank burst open. The plumber, leaning over the water tank to perform some task, was cut and killed by the "shrapnel" formed when the water tank burst. - ED.

Examples of water tank and similar pressure relief valves include

  • Watts 53 pressure relief valves in 1/2-in NPT and 3/4-in NPT. Model 53L includes a test or relief lever. Quoting from Watts® product literature for this product:

Watts Series 53 Pressure Relief Valves are spring operated bronze relief valves designed to be used only as protection from the build up of excessive pressure in systems containing water, oil or air. These valves are not ASME approved safety relief valves and should not be used in system applications with this requirement.

They feature all bronze construction with stainless steel springs. Series 53 have standard pressure settings of 75, 125, and 150psi (5.2, 8.6 and 10.3 bar). They are also specially available at 50psi (3.4 bar) setting. Pressure range is 75-175psi (5.2-12.1 bar). - Watts®

  • Watts530C (calibrated pressure relief valves) and LF530C, lead free calibrated pressure relief valves. Product literature quote:

    Series LF530C Lead Free* Calibrated Pressure Relief Valves are used in commercial, residential and industrial applications to protect against excessive pressure in systems containing water, oil, or air. It consists of a Lead Free* brass body construction with NPT threaded male inlet and NPT threaded female (drain) outlet connections, stainless steel spring, brass bonnet, Buna-N disc, and Buna-N O-ring. Series LF530C has a calibrated adjustment feature for setting the valve to the required relief pressure, and is ideal for by-pass thermal expansion pressure relief (not ASME approved).

    Maximum Pressure: 300psi (20.67 bar). Adjustable Pressure Ranges: Sizes 1/2, 3/4 in. - 50 to 175psi (3.45 to 12.06 bar), Size 3/4 in. - 100 to 300psi (6.89 to 20.67 bar).
    - Watts®

    These valves are also used for bypass thermal expansion relief as we describe below at the Watts 30L.

  • Watts 30L Pressure Relief Valves for Well Systems, with test lever. These valves, intended for protection against excessive pressure in well water systems, are designed for pressure relief only [compared with pressure and temperature relief valves that should be used on water heating equipment -
    see RELIEF VALVE, WATER HEATER

    or RELIEF VALVE, TP VALVE, BOILER relief valves used on heating boilers

    Quoting from Watts product literature:

    Series 30L Pressure Relief Valves for Wells are used to protect against excessive pressures in well systems. It is not diaphragm actuated and is used for pressure-relief service only.

    Series 30L consists of a bronze body construction with NPT threaded male inlet and NPT threaded female (drain) outlet connections, stainless steel spring, and test lever. Standard Pressure Setting: 75psi (5.17 bar), Optional Settings: 100, 125, and 150psi (6.9, 8.6, and 10.3 bar). - Watts®

    These valves are installed as an auxiliary bleeder pressure relief valve to provide relief of increased water pressure due to thermal expansion, and they are typically installed on a hot water supply pipe downstream from the water heater and over a laundry sink or drain. Watts points out in their product literature that these valves are also installed on cold water piping.

But check with the manufacturer of your water tank to determine if a different relief valve opening pressure is required.

Standard water tank pressure relief valves are sold at plumbing suppliers and are pre-set with a "safe" pressure for most home water tanks, provided that the water tank, piping, and controls are properly installed and adjusted. A professional plumber would select and install a water tank pressure relief valve that opens to spill water and relieve pressure at a point well below the rated burst pressure of the tank.

The burst-pressure of a water tank, provided it's undamaged and properly installed, should be well above the opening pressure on the tank relief valve. But to choose a specific valve matched to your water tank, you should consult the manual for your water tank and pump and their manufacturer to be sure you've got the right part.

Watch out: If a pressure relief valve is not installed on your water tank ask your plumber to provide one promptly.

 

Continue reading at WATER TANK SAFETY or select a topic from the More Reading links shown below.

Or see WATER TANK: USES, TROUBLESHOOTING

Or see WATER PUMP PROTECTION SWITCH

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