Water Tank Pressure Relief Valves

Can a water pressure tank explode? Yes!

Leaky Water Tank Pressure Relief Valve Safety Warning

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 the Right Water Tank Pressure Relief Valve for Water Storage Tanks or Water Pressure Tanks

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

Our reader asked:

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]

Water Pressure Tank Explosion Fatalities

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. - personal communication, Steve Vermilye to Editor ca 2001.

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.

Here are additional reports of injuries or deaths caused by exploding water pressure tanks.

• Chester New York Police Dept. Water Treatment Plant Explosion - King Tract Development [PDF] Town of Chester, NY Police Department, - retrieved 2021/04/19 original source: https://local.nixle.com/alert/4894709/
  
  Quote:
  
  At 6:30PM on Tuesday, the Town of Chester Police responded to a report of an explosion in the King Tract development off of Laroe Road. Residents in the area were reporting that they had no water. It was determined that the water treatment plant for the development had exploded.
  
  Chester Fire Department responded to the scene and were assisted by Orange County Fire Investigators. No evidence of criminal activity was detected.
  
  The water holding tank is pressurized by a compressor to send water to the residences. Preliminary investigation reveals that the tank failed and the internal pressure blew the end of the tank off and through the attached treatment building, completely demolishing the building.
  
  The water system that serves the area is privately owned by 473 West End Realty Corp. The water system owner has indicated that drinking water will be available to the residents from a water tanker later today.
  
  Address/Location Town of Chester, NY Police Department 79 Laroe Rd Chester, NY 10918
• Fox News "Two Killed From 300,000 Gallon Water Tank Explosion" Fox News, Tel: (888) 369-4762, April 07, 2011 - retrieved 2021/04/19 original source: https://www.foxnews.com/us/two-killed-from-300000-gallon-water-tank-explosion
  Excerpt:
  
  Two men died Thursday when a 300,000 gallon water tank exploded in Florida, unleashing a flood and causing an adjacent building to collapse. The victims were in the midst of repairing a pump that filled the tank inside an adjacent concrete block building.
  
  The force of the water from the explosion caused the building to collapse, MyFoxTampaBay.com reported.
  
  [Note: event occurred in Lake Placid Florida, original article not found - Ed.]
  
  Highland County Sherriff's Office, WATER TANK RUPTURE FINAL UPDATE [PDF] Nell Hays, P.I.O. Highlands County Sheriff’s Office 434 Fernleaf Ave. Sebring, FL 33870 863-402-7369 retrieved 2021/04/17 original source: http://www.highlandssheriff.org/document_center/Press_News_Release_Water_Tank_Final.pdf
  
  As previously reported, a 300,000 gallon ground level water tank ruptured on Thursday, April 7th at the former Georgia Pacific industrial plant located at 400 State Road 70 in Lake Placid. The resulting wave of water severely damaged an adjacent concrete block building where two United-Fire workers were making repairs on a pump. The workers, identified as Jon Martinez and Jason Steele, were killed in the partial collapse of this building. At this time the case remains open however further investigation has been turned over to the Department of Environmental Protection (DEP) and the Occupational Safety and Health Administration (OSHA).
• HeatingHelp.com, "Fatal Airing up of Water Tank", reported by Jughne, September 2016 - possibly anecdotal, no corroboration found, retrieved 2021/04/19 original source: https://forum.heatinghelp.com/discussion/158963/fatal-airing-up-of-water-tank
  
  Excerpt: About a week or two ago a local rancher was killed while adding air to his well water pressure tank.
  
• Karpen, R.J., "Investigation of a Water Pressure Tank Explosion", Minnesota Department of Health, Mankato MN, October 1940, retrieved 2021/04/19 original source: https://awwa.onlinelibrary.wiley.com/doi/abs/10.1002/j.1551-8833.1940.tb19589.x
  
  Excerpt:
  
  On December 14, 1938, the water pressure tank of the municipal water supply of Bricelyn Minnesota exploded, wrecking the pump house and tank. The explosion occurred at 1 AM just as the pressure gauge indicated pressure nearest 60 pounds and the pump was about to shut off.
  
  The possibility that the zinc lining in the pressure tank was a contributing factor to the explosion was indicated in an investigation report conducted by the Minnesota Department of Health.
  
  The Bricelyn water supply, prior to this explosion, was obtained from a drilled well from which the water was lifted by means of air and discharged into a small receiving tank. A centrifugal pump was used to force water from the receiving take into the pressure tank and distribution system.
  
  This pump had a rated capacity of 250 gpm, and was designed to operate up to a maximum head of 60 psi.
  
  It was the practice of the operator to maintain the water level in the tank at about 4 in. above the center. This he accomplished by pumping at approximately two-hour intervals from 7:00 AM to 3:00 PM, at 6:00 PM, 8:30 PM, and at midnight. The daily consumption of water was about 18,000 gal. The pressure tank, 8 ft. in diameter and 36 ft. long, had been in service for 36 years. It was provided with a pressure relief valve which when tested opened at a pressure of 66 lb. psi.
  
  Eight or ten onths prior to the explosion, a leak developed in an end seam at the bottom of the tank.
  
  After the tank was drained and inspected it was found that the portion of the tank which had been in contact with the water was petted and corroded. It was then reconditioned by welding the defective same and it's interior surface was coded by spraying it with molten zinc.
• KHOU-TV, "Worker killed in church water tank explosion", KHOU 11 News 5718 Westheimer Rd Houston, Texas 77057 USA Website: https://www.khou.com/ Tel: (713) 526-1111, 18 August, 2011
  
  TOMBALL, Texas A worker was killed Tuesday after a water storage tank exploded near Tomball. It happened at the Salem Lutheran Church, at Lutheran Church Road and FM 2920.A spokesperson for the church said the injured man was working on the 20-foot-tall tank when the blast happened.
  
  The force of the explosion caused the worker to fall and ripped the lid off the tank. - original source https://www.khou.com/amp/article/news/worker-killed-in-church-water-tank-explosion/285-341096970
• Yannaccone, John R., P.E. "PRESSURIZED WATER TANK EXPLOSION" DJS Associates, John R. Yannaccone, P.E., Senior Mechanical Engineer with DJS Associates, Inc., Email: experts@forensicDJS.com Tel: 215-659-2010.- retrieved 2021/04/19 original source: https://www.forensicdjs.com/blog/pressurized-water-tank-explosion/
  Excerpts:
  
  A worker was operating a system used to supply water from a tank mounted on a utility vehicle. Instead of using a pump, this system used a 120-gallon water tank, which was pressurized from a compressed air cylinder.
  
  The air pressure pushes water out of the tank, referred to as an “air over water” system. While operating the system, a worker near the vehicle was blown 20 feet from where he was standing.
  
  He sustained severe blunt force trauma and died as a result of his injuries. Photographs from the incident showed that the end of the water tank dislodged from the main portion of the tank.
  
  Expert Analysis: An inspection of the system revealed that the tank was in good condition, with no signs of corrosion or other damage. The 120-gallon water tank had a label indicating the maximum working pressure for the tank was 75 psi and must be equipped with an adequate size pressure relief valve; however, there was no pressure relief valve in this system.
  
  ... it was determined that the pressure regulator failed during operations, allowing air to continuously flow into the tank. The lack of a pressure relief valve allowed the tank pressure to increase until the tank failed.
  
  

Steps to install or replace a water tank pressure relief valve?

Our InspectApedia reader asked:

Good info. Every other site only talks about the Water Heater pressure relief valves.

Where is the information / steps on how to replace the pressure relief valve on the water tank? On 2011-06-05 by steve

Here are the steps in replacing a water tank pressure relief valve

Steve: good question. Until you asked I had not detailed the steps in replacing a water tank pressure relief valve.

The procedure to replace a water tank pressure relief valve is easier than installing a new one because the tee or fitting where the valve will be should already be in place.

For readers installing a new water tank pressure relief valve, look for a fitting like the one where the pressure gauge is mounted in our photo above. You may find that a tapping for the relief valve is already in place and is simply plugged with a pipe pllug.

If your water pipes where the pressure relief valve is installed are in reasonably good condition, not badly rusted or corroded, removing a pipe plug to install a new relief valve, or replacing an existing pressur tank relief valve should be straight forward as the following steps.

Assuming that the pressure relief valve is mounted at the bottom of your water pressure tank such as shown in my photo.

1. If your well pump is above ground, set aside a bucket of clean water to use in case you need to re-prime the pump at the end of this job.
2. Turn off the pump
3. Close water valves between the pressure tank and the building - this will reduce the amount of water draining to be done. If you can do this you can skip step 4 and go to step 5 below.
4. Drain water pressure off of the water system (if you didn't do step 3) by opening hot and cold water supply valves at the lowest fixtures in the building.
5. Drain the water tank - details are at WATER TANK DRAIN VALVE 
   
   Notice in the photo above that we have a hose temporarily attached to the water tank drain valve so that water can easily be directed outside rather than onto the floor. This can be helpful as usually this drain valve is too close to the floor to get a bucket underneath it.
6. Unscrew the existing pressure relief valve - you shouldn't need more than ordinary plumbing tools or simply an adjustable wrench
   
   Watch out: take care when unscrewing the relief valve: if force is needed use two wrenches: one to hold the fitting into which the valve screws and a second to turn the valve counter clockwise. (I'm avoiding bending or damaging the water lines into which the relief valve is screwed).
7. Using teflon tape or pipe dope, prepare the threads on the new valve and screw it in place.
   
   Watch out: be sure you've bought a water tank pressure relief valve of the appropriate size and capacity. Examples are given just below in this article.
8. Close any drain or house fixture valves that are open.
9. Turn the water or well pump back on to restore water pressure.
   
   Or if your water pump is an above ground jet pump t might need to be primed.

Sources / Examples of water tank and similar pressure relief valves

• 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.