Pressure Release Valve on a Water Heater

[mestrezat]

The pressure release valve has failed on my 30 years old water heater. One day, it just decided to start spewing water under our floor boards. Our water pump went crazy. Glad we were on board at the time. I took off the end cap where the water was coming from and installed a screw on cap in it's place stopping the leak. Now at least we have water.
I'm looking for a source for a replacement and have found some for RV's but their pressure is preset at 170 pounds of pressure which I'm sure my system with it's tiny little Jabsco pump would never get close to even in the worst of situations.
Anyone have any idea where I can get a replacement valve that would be closer to the pressure of a boat water system? Not may available out here in Fiji so I'd have to get one shipped in.

[matauwhi]

G'day, mate. The pressure rating of the relief valve is not totally based on the pump pressure of the system. For example, if you were heating it using electricity and the temperature cutoff failed, the temperature would go above 212 deg F, creating steam and significantly increasing the pressure in the system. Likewise, if you were heating the water using the engine and the heat exchanger and cooling system on the engine failed. This could cause the heater to burst (or explode in some cases).

Sometimes, you can replace the relief valve with one similiar to that of a typical household water heater if the pressure rating, thread dimensions and sensor length are the same. You might want to check at the local hardware store near you in Fiji. Cheers.

[captain465]

Look at the tag on the old valve..........it will tell you what the reliefe pressure should be. Watts is a vendor of water heater pressure relief valves. Get one as soon as possible.....with a plug in place of the valve, you are sitting on a bomb!!!

[donradcliffe]

Pressure Relief Valve

It says its setpoint is 75 psi and 210 degrees F, which is a little weird, as the saturation temp at 75 psi is 320 degrees. The 75 psi would have probably blown the hoses off my heater, and the 175 surely would.

[Mr B]

Try the boat shops in Lautoka, You might be lucky,

[GordMay]

The Temperature and Pressure (T&P) relief valve is a safety device that serves two functions. It is designed to open and relieve water should the pressure in the water heater exceed the rated working pressure of the tank, usually 150 psi in shore-side household systems; but (apparently) 75 psi in yours.
It will also open in the event that the temperature in the tank exceeds 210°F (standard).

If the T&P valve opens due to excess pressure, there will be either dripping or a small continuous flow of water that relieves the pressure.

If, on the other hand, it opens due to a high temperature condition, the valve will open completely and allow the whole tank to empty until cool water resets the thermal probe on the T&P.

Both excessive pressure and high temperatures in water heaters are extremely hazardous.

Elevated water pressure can be caused by thermal expansion*, a backflow preventer in the supply side, and/or high incoming water pressure (shoreside supply). These conditions can be managed by installing a thermal expansion tank and/or a pressure reducing valve in the system.

High water temperature can be remedied by replacing the thermostat.

In addition, the T&P valve may discharge (usually a drip, rather than a free-flow gush) because calcium (lime) or sediment has accumulated in the valve, preventing it from seating properly.

The T&P valve pressure setting must not be greater than the working pressure of the water heater, and must be higher than input of the water heater respectively. Accordingly, check your water heater pressure rating (75 psi?) - and do not exceed this psi rating with a hardware store replacement (150 psi).
If your tank is rated at 150 psi, then you csan substitue any "standard" 150 psi/210°F T&P Relief Valve, that fits.

[SV Demeter]

Originally Posted by mestrezat

The pressure release valve has failed on my 30 years old water heater. One day, it just decided to start spewing water under our floor boards. Our water pump went crazy. Glad we were on board at the time. I took off the end cap where the water was coming from and installed a screw on cap in it's place stopping the leak. Now at least we have water.
I'm looking for a source for a replacement and have found some for RV's but their pressure is preset at 170 pounds of pressure which I'm sure my system with it's tiny little Jabsco pump would never get close to even in the worst of situations.
Anyone have any idea where I can get a replacement valve that would be closer to the pressure of a boat water system? Not may available out here in Fiji so I'd have to get one shipped in.

Might help to know what brand of heater it is ie Raritan, Isotemp etc. As to your comment about being lucky you were on board when it happened you might want to consider turning things like the water pump off when not onboard as any other seemingly minor plumbing issue could result in dumping all of your FW supply into the bilge.

[roberttigar]

I replaced a Raritan T &P valve with 1 from home depot about 3 years ago. Has worked just fine since then. Bob

[Tripod]

Originally Posted by roberttigar

I replaced a Raritan T &P valve with 1 from home depot about 3 years ago. Has worked just fine since then. Bob

I hope the pressure rating of the valve is below the pressure rating of your tank, otherwise, it's no better than a plug and you're sitting on a bomb too.

[GordMay]

Originally Posted by roberttigar

I replaced a Raritan T &P valve with 1 from home depot about 3 years ago. Has worked just fine since then. Bob

Originally Posted by Tripod

I hope the pressure rating of the valve is below the pressure rating of your tank, otherwise, it's no better than a plug and you're sitting on a bomb too.

Indeed, Tripod!!!

[sailorchic34]

Gordy is spot on once again...

Very Important to have a temperature and pressure relief valve sized for your heater. For typical boat systems the 75 psig and 210 degree F sounds about right. Home water heaters are sized for 100 psig working pressure. Marine water heaters for the most part operate at a lower pressure, 35-40 psig.

Really important to get the T&P relief and not just a pressure relief. Big difference. If the thermostat failed to open the heating element could heat the water to above 212 degrees where the water turns to steam, so not good. A water heater explosion, even a dinky 6 gallon unit would be just like a bomb going off and would destroy the boat, house or factory building (as has happened in the past).

Never use a T&P relief rated at 150 psig unless the water heater is ASME stamped, which all boat and residential heaters ARE NOT! Residential heaters are rated at either 100 psig or 125 psig.... ASME stamped is only available on better commercial water heaters. (Thats for the USA btw and other countries would be difference of course)

[Cheechako]

So.... I've often wondered about this.... is the danger from air trapped in the system? Having worked in aerospace bulge forming (water pressurized up to 10,000 psi), I can tell you that there is very little danger from pressurized water. As water doesnt compress, any little leak relives the pressure very quickly. We often had problems with breaking metal or welds with parts pressurised 2-3000 psi. The result is like a squirt gun squirt and the psi is gone...... Many of our dies were open concept so you could actually stand there and watch it occur.

[sailorchic34]

You are quite correct about pressurized water, not a problem. No the problem is when the water temperature gets above 212 degrees F, the water will boil and the pressures will rise very quickly and the water will flash into steam.

Failure mode is for the shell to fail along a seam via expanding steam vapor. It has destroyed buildings and sent 40 gallon residential water heaters hundreds of feet into the air.

That's why every water heater in the US has a T&P, Temperature and pressure relief valve.

BTW like electric circuit breakers, pressure relief valves should be tested / tripped every so often to verify that the valve will actually open. Many old ones will not open at rated pressure or temp due to liming, corrosion.

[Millerslocal]

We want to replace the pressure relief valve on our Quick Nautic B3 boiler. There are no markings on the current valve. It is available from Quick but no specs of it provided on their website. We are based in a remote location so shipping one in will be complicated and costly. How do I work out what generic I can replace it with? The boiler manual says it has a working pressure of 600kpa. My water pump has a high pressure cut off of 210kpa. Based on that what specs would my new pressure relief valve need to be?

[GordMay]

A water heating device is generally considered to be a “boiler”, when it reaches an operating pressure of about 1100kPa (160 psig), or an operating temperature of 99 degrees Celsius (210 deg F), etc.

What you have (600kPa), is technically a water heater.

I’d ask sailorchic34 to correct or confirm that:
The pressure-relief component of a TP valve, or of a separate additional pressure-relief valve should be at least 20 to 30 psi above the maximum working pressure in the system. The standard opening pressure for TP valves (on residential water heaters) is usually 150 psi (1034 kPa), and most water heater tanks also have a standard operating pressure of 150 psi.
The standard maximum temperature rating for a T&P valve is usually 210°F (99C).

1 psi ≈ < 6.9 kPa