Water Tank Pressure Relief Valve FAQs

Causes of & Safety Warnings About Water Spraying Out at a Cold Water Pressure Relief Valve Q&A

After we turn off the shower water spills at the water tank relief valve

Why would water blast out of the valve in a pressure tank?

I noticed that my shower had much better water pressure. Then shortly after my shower was finished I heard the water being released out of the tank and into the basement. (July 27, 2014) Anonymous

Reply: by Moderator with a safety warning

Anon,

Watch out: if water is pouring out of the pressure relief valve on your water tank system then the pressure control switch is allowing a dangerously high over-pressure in the system that can burst the water tank or water pipes, flooding the building and injuring anyone who might be neaerby.

From your description I think this is probably what's happening.

Here's what to do:

If you have municipal water supply from a city or town or community water system then your water pressure regulator either needs adjustment or replacement.

See WATER PRESSURE REGULATOR ADJUSTMENT

If your water is supplied by a private pump and well and water tank system then your pressure control switch is not working properly and needs repair or replacement or adjustment.

Sometimes silt and debris can clog the pressure control switch causing to tail to respond properly to the actual water pressure, and as I've warned above, that's dangerous.

See WATER PRESSURE CONTROL SWITCH ADJUSTMENTS - Daniel F.

 

Tell me Why Our Water Tank Pressure Relief Valve at the well is Spraying Water

What is the function of "PRVNL 75" 75 PSI above the domestic water well. Does it suppose to spray the water on water the cement slab on normal bases. On 2018-03-14 by Sam

Solution by (mod) -

Sam
You are asking about a PRV = Pressure Relief Valve

Your water tank's pressure relief valve is designed to open if water pressure exceeds 75 psi. At higher pressures the valve opens to relieve pressure, spilling water onto the floor (preferably at or near a floor drain).

Watch out: The Pressure Relief Valve on a water pressure tank or at the well prevents the tank or piping from exploding should a water pump fail to turn off - such breakages can injure or kill someone nearby.

The pressure relief valve opening pressure would be below the pressure tank's burst pressure but higher than usual water system pressure.

If your PRV is spraying water your system is unafe and needs immediate help from a licensed plumber. I'd turn it off as I suspect your well pump is running continuously.

The proper repair is to adjust or replace the well pump pressure control switch, explained at WATER PRESSURE CONTROL SWITCH ADJUSTMENTS - Daniel F.

 

If the water tank relief valve is leaking do we have to leave water turned OFF?

Should water be turned off until valve is replaced? On 2020-03-21 by pat

Answer by (mod) - not necessarily but beware of unsafe water pressure

Pat

Before requiring turning off the water I'd want to understand what problem we're having.
For example

IF the valve is dripping slowly - not a catastrophic leak - b(ut repair is needed soon - else dripping water can leave mineral salts behind that ultimately clog the pressure relief valve,leading to an unsafe condition)

AND IF the tank pressure is in the normal operating range (say no more than 60 or 70 psi and well below the maximum safe pressure on the tank label)

THEN you can live with the leak (catch it) until the valve can be replaced.

Watch out: BUT if there is a gushing leak or if there is abnormally-high tank pressure then the system is unsafe and the water oyno should be turned off and pressure relieved by opening a faucet. The risks are a burst pipe and flooded building or a burst water tank that injures someone nearby.

Relief valve goes off when the pump turns on and off a few times

After the pump runs several times the relief valve goes off. Is this due to too much air pressure or to less air pressure? When I press the air valve (where you would add air) water comes out no air. Any help would be appreciated. Thanks (Dec 18, 2014) Rick said:

Reply:

Rick you could be seeing an abnormal pressure increase in the system, e.g. if the pressure switch is not operating properly, or you could be seeing the effects of water hammer.

See WATER HAMMER NOISE DIAGNOSE & CURE

Why is my new pressure relief valve leaking

I replaced the water tank relief valve. But the new one is leaking just like the old one did. On 2017-10-26 by Mike E.

by (mod) - possibly water pressure is too high

Mike,

Take a look at the pressure and temperature in the system.

Watch out: If those are what is causing the relief valve to spill then the system is unsafe and it needs to be shut down immediately to avoid risking an explosion, such as a boiling liquid Vapor or on a water heate, a dangerous bleve explosion

Reader Questions Whether or Not a Leaking Relief Valve is Dangerous

Not a plumber but I respectfully question the statement that a "leaking" pressure relief valve is dangerous and should be replaced.

The valve may be doing exactly what it was designed to do; bleeding off an overpressure condition. A neighbor replaced his irrigation system leaking 75 psi valve with one that was adjustable. He then adjusted the release pressire until it no longer leaked. Fortunately there was no one around when the tank burst. On 2016-09-21 by H West

by (mod) -

H. West:

Thank you for commenting but

Watch out: you are seriously mistaken - an error that could result in a BLEVE explosion, property damage, even death to people nearby should such an explosion occur.

There are several concerns but a basic one is that water leaking from a pressure/temperature relief valve risks leaving deposits, often mineral scale as is shown in many photographs of leaky relief valves at InspectApedia.com.

Ultimately enough scale accumulates in a relief valve that the valve spring becomes jammed: the valve will no longer open at the proper temperature and pressure, and in fact may fail to open at all - thus a BLEVE.

On a cold water system whose relief valve is rated just for pressure - such as on a water supply system pressure tank, where temperature is not a factor - leaks can also deposit debris, silt, corrosive materials that could block a valve, though I suspect that the risk of blockage is reduced by the absence of heat. Heat speeds the deposits of mineral scale at points of leakage.

Water Pressure Relief Valve Selection & Installation Q&A

Can I use a reducer nipple to connect a 1-inch pressure relief valve with a 1/2-inch unit?

I have a well water 1 inch relief valve with a 0.5 inch output.

It is leaking and would like to buy another, but cannot find one. Also my water tank holds 50 gal and the tank pressure should be 40psi.

Should I be looking use a reducer from 1: to3/4" and buy a 3/4" relief valve set for around 100psi On 2018-10-31 by Dan

Safety warning by (mod) -

Dan I'm not entirely clear on what is your situation, but

Watch out: if you have a 1" diameter pressure relief valve it is unsafe to downsize its discharge to 1/2" - one should never restrict the discharge opening of a safety pressure relief valve as doing so can cause a tank to burst, injuring someone nearby.

Please read and follow the installation instructions on your tank relief valves.

I see plenty of discussion about the set pressure of relief valves. Obviously that number is important, but just as important is the relief valve (rv) capacity rating. If a RV opens and does not allow sufficient fluid out fast enough, it still can allow the tank to build pressure.

Pressure that still may exceed the vessel. Cold water system RV's should be rated in gallons per minute (gpm) and beable to relieve the out volume of the supplying pump.

Please read and follow the installation instructions on your tank relief valves. Most fluid (not air) system relief valves require that they are installed vertically. It does many a difference depending in the valve design. On 2017-04-02 by Tony V

by (mod) - TPR valves on HEATING EQUIPMENT are rated typically in maximum BTUH

Thanks for the comments, Tony. I agree and add that TPR valves are rated typically in maximum BTUH - a number that should be greater than the input BTUH of the heating device they are protecting.

But pressure relief valves used on water pressure tanks - i.e. not hot water vessels - are rated at an opening pressure that must be below that of the burst pressure or maximum rated permitted pressure of the water storage tank or pressure tank.

 

Does it matter whether the pressure gauge is upstream or downstream from the relief valve?

Does it matter the order in which the pressure relief valve and the pressure gauge are installed? If so, then which one should be "upstream", and which "downstream"? Thank you! Best regards, Robert B. On 2015-11-28 by robertb

Answer by (mod) -

Use a tank tee - that will give you typical placement of the components.

In general always keep the relief valve close to the tank.

Can I screw a boiler drain valve into my pressure relief valve?

(Aug 22, 2014) Anonymous said:
Can't seem to find a pressure relief valve that operates as a cutout switch ONLY.

Want a 100# releif valve that will cutout a runaway pump but not cut back in at lower pressure.

(Sept 20, 2014) Larry G said:
Can I screw a boiler drain valve into my pressure relief valve? There is a threaded port available.

Reply:

Larry

NO!!

Watch out: What you describe could cause a BLEVE explosion destroying the boiler, building, and injuring or killing someone.