Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 02-02-2012, 20:12   #1
Registered User

Join Date: Jul 2007
Location: Bonaire
Boat: Shin Fa 458 Custom Cutter but looks like a Liberty 458
Posts: 346
Pressure Release Valve on a Water Heater

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.
__________________

__________________
mestrezat is offline   Reply With Quote
Old 02-02-2012, 20:25   #2
Registered User
 
matauwhi's Avatar

Join Date: Jun 2010
Location: Bay of Islands, New Zealand
Boat: Mason 53
Posts: 652
Re: Pressure release valve on a water heater.

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.
__________________

__________________
matauwhi is offline   Reply With Quote
Old 02-02-2012, 21:02   #3
Registered User
 
captain465's Avatar

Join Date: Mar 2007
Location: Ft Lauderdale, FL
Boat: 38ft Irwin center cockpit sloop MERIDIAN
Posts: 619
Re: Pressure release valve on a water heater.

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!!!
__________________
Do not go where the path may lead.........
go instead where there is no path........
and leave a trail.
Ralph Waldo Emerson
captain465 is online now   Reply With Quote
Old 02-02-2012, 21:04   #4
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,334
Re: Pressure release valve on a water heater.

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.
__________________
donradcliffe is offline   Reply With Quote
Old 02-02-2012, 21:30   #5
Registered User

Join Date: Aug 2011
Location: Melbourne Australia
Boat: Paper Tiger 14 foot, Gemini 105MC 34 foot Catamaran Hull no 825
Posts: 1,616
Re: Pressure release valve on a water heater.

Try the boat shops in Lautoka, You might be lucky,
__________________
Mr B is offline   Reply With Quote
Old 03-02-2012, 08:06   #6
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,586
Images: 240
Re: Pressure release valve on a water heater.

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 210F (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/210F T&P Relief Valve, that fits.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 03-02-2012, 08:22   #7
Registered User
 
SV Demeter's Avatar

Join Date: Dec 2009
Location: Cruising Eastern Caribbean
Boat: Wauquiez Amphitrite 43- Demeter
Posts: 1,164
Re: Pressure release valve on a water heater.

Quote:
Originally Posted by mestrezat View Post
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.
__________________
SV Demeter is offline   Reply With Quote
Old 03-02-2012, 08:25   #8
Registered User

Join Date: Oct 2008
Posts: 205
Re: Pressure release valve on a water heater.

I replaced a Raritan T &P valve with 1 from home depot about 3 years ago. Has worked just fine since then. Bob
__________________
roberttigar is offline   Reply With Quote
Old 03-02-2012, 09:23   #9
Registered User
 
Tripod's Avatar

Join Date: Aug 2010
Location: St. Augustine, FL
Boat: Morgan Out Island 415
Posts: 220
Re: Pressure release valve on a water heater.

Quote:
Originally Posted by roberttigar View Post
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.
__________________
[SIGPIC][/SIGPIC]
"Without question, the greatest invention in the history of mankind is beer. Oh, I grant you that the wheel was also a fine invention, but the wheel does not go nearly as well with pizza." Dave Barry
Tripod is offline   Reply With Quote
Old 03-02-2012, 09:45   #10
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,586
Images: 240
Re: Pressure release valve on a water heater.

Quote:
Originally Posted by roberttigar View Post
I replaced a Raritan T &P valve with 1 from home depot about 3 years ago. Has worked just fine since then. Bob
Quote:
Originally Posted by Tripod View Post
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!!!
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 03-02-2012, 10:18   #11
Moderator
 
sailorchic34's Avatar

Cruisers Forum Supporter

Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 4,815
Re: Pressure release valve on a water heater.

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)
__________________
sailorchic34 is offline   Reply With Quote
Old 03-02-2012, 10:41   #12
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,369
Re: Pressure release valve on a water heater.

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.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is online now   Reply With Quote
Old 03-02-2012, 17:54   #13
Moderator
 
sailorchic34's Avatar

Cruisers Forum Supporter

Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 4,815
Re: Pressure release valve on a water heater.

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.
__________________

__________________
sailorchic34 is offline   Reply With Quote
Reply

Tags
water

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cruisers: Pressurized Fresh Water ? Beersmith Plumbing Systems and Fixtures 80 22-11-2011 02:46
Refilling Water Tanks ironhorserider2 Plumbing Systems and Fixtures 19 29-09-2011 07:01
Water Heater Siphoning Through Engine RussR Plumbing Systems and Fixtures 9 13-09-2011 16:14
Building a Pump for a Watermaker Lars_L Plumbing Systems and Fixtures 2 22-08-2011 12:51
Send Over-Pressure Shore Water Over the Side with Pressure Valve ? sdowney717 Plumbing Systems and Fixtures 4 15-08-2011 19:36



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:40.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.