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Old 09-02-2015, 11:07 AM   #21
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Dicky is right, you won't lose the air cushion by releasing air from that valve, it sits well below the top of the hot water tank. I'm not sure what's going on but since this is happening on gas and electric it is probably not the thermostat.
I personally would install a good quality pressure regulator with a set screw, not the plastic cheapos they sell in some big box store, and set it to 30 - 40 psi that is all you need. A pressure regulator adjusts the pressure, it does not affect the flow.
Another option would be to fill the fresh water tank, turn the city water off and use the built in water pump and see if that makes a difference. Next, if that doesn't work I would install a pressure accumulator.
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Old 09-05-2015, 06:43 PM   #22
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Originally Posted by VinceU View Post
DISAGREE WITH SOME OF YOUR POINTS. The aircushion is designed in by Atwood and Suburban otherwise they would tap the tank top for more volume.
I'm sorry about that, but please allow me to respond. This of course is way beyond the OP question but may prove useful.

FWIW we do sometimes use water heaters with the taps on the side due to height space limitations. The side taps are not at the very top because there is insulation surrounding the water heater and the tank under the insulation is more of an oval shape, not the squared off shape the jacket is. If the side tap was at the very top it would only be able to connect to the tank with a special angle fitting, not the standard and inexpensive weld o let commonly used. So while I do not know for certain why Atwood and Suburban use water heaters with side taps, I would think because of space constraints and ease of service. Also no matter whether the top of the tank or the side of the tank is tapped, the volume of a given tank would be the same.

As for the statement " MOST UNITS COME FROM FACTORY 130-140 F " I'm sure they do. I only wanted to point out the risk of burns increases quickly when water temperatures are above 120deg F.

As for the statement "RELIEF VALVES ARE SET TO 135 PSI " I submit a picture of the relief valve on my unit, which is a very common Watts 100XL. It states it is set to 150psi and 210deg F.

As for the statement "WATER AND AIR ARE INSOLUABLE, DIVERS BUBBLES RISE TO THE TOP. THERE IS A GOOD REASON RV WATER HEATERS OUTLET IS TAPPED ABOUT 25% FROM THE TOP, ALLOWS AIR SPACE, SAME FUNCTION AS A ACCUMULATOR. NOTE HOME HEATERS TAP THE TOP OF THE TANK, NO AIR SPACE." Air will quickly become entrained in water as the water is heated. So much so that a required element of any water space heating system is an air separator. I submit a Google search results page that supplies various education based links that discuss how air will dissolve into water https://www.google.com/#q=is+air+soluble+in+water I'm a little confused about the reference to divers bubbles, I assume that means air will rise to the top of a water filled vessel. I allready answered why a water heater with side taps does not have the tap at the top. I think the term accumulator may not be used correctly here, an accumulator usually refers to some sort of energy/potential storage device. https://www.google.com/#q=what+is+an+accumulator Do you mean expansion tank instead? Please note most, but not all home water heaters have the connections at the top of the tank.

Why do we not have the same problems as the OP had in our homes? Because the water heater in our home does not usually go from cold water to setpoint and there is not a check valve; like we have in our trailers; in our homes. This allows the water heating in our home water heater to expand back into the cold feed. Our home water heater's temp usually varies only about 10-15deg F, unless it is sized incorrectly.
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Old 09-06-2015, 10:15 AM   #23
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Here 's my final submittal, fresh from the Internet blog channel of proper RV operation. I'm Out!!



"RV WATER HEATERS AND MOTORHOME WATER HEATERS

The majority of RV water heaters and motorhome water heaters are either Suburban water heaters or Atwood water heaters. RVs, which do not have Suburban or Atwood water heaters, are usually high end motor homes which may have either instantaneous water heaters or some type of engine assist water heaters. Here we’re going discuss leaking, weeping water heaters, or more specifically weeping pressure temperature relief valves. (Commonly referred to as P&T relief value)


P&T relief valves can be an area of confusion for Rv’ers until they understand the purpose and function of the P&T valve and whether or not they are functioning properly. In other words a P&T valve which is always weeping way not necessarily be bad. Let me explain why.

PURPOSE OF P&T RELIEF VALVE

RV water systems are closed systems, which mean there must be a means of relieving excess pressure when it develops. The obvious question then is what would cause excess pressure to develop in the tank. We know H2O expands when heated so we might then conclude there is always excess pressure in the water tank. This is true…only to a point however. A properly functioning RV water heater always has an air expansion pocket in the top of the tank. What is an air expansion pocket? It is simply an air pocket, which naturally forms in the water heater tank when it is filled.

As long as this air expansion pocket is of sufficient size, the only time the P&T relief water valve will weep is during the heating cycle. However, as hot water is taken from the tank the size of the air expansion pocket will diminish eventually to the point where the tank is practically full of water. When it reaches this point the inside pressure of the tank will almost always be excessive ( over the 125/150 psi rating for the P&T valve) resulting in excessive weeping of the P&T valve.

Rv’ers not aware of this may mistakenly conclude the P&T valve is bad when it is not. To further complicate matters they may replace the valve and in the process re-introduce an adequate air expansion pocket and then it will naturally work fine…until the air expansion pocket is diminished again and the whole process repeats itself. Rv’ers replacing numerous P&T valves are most likely doing it needlessly. So what is the answer?

Reintroduce an adequate air expansion pocket and this is how it is done:

1.Turn water heater off.
2.Turn off water supply (city H2O or H2O pump)
3.Open closest hot H2O faucet in RV.
4.Open the P&T valve by pulling on handle at end of valve and allow H2O to flow until it stops.
5.Release handle on P&T valve – it should snap shut. ( do this a couple of times as it may stick)
6.Close hot water faucet.
7.Turn on H2O supply – Now that everything is closed the tank will refill and air expansion pocket will be re-established.
Repeat the above procedure if P&T valve continues to weep between heating cycles. If this is not successful then the P&T valve should be replaced. "

Vince


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Old 09-06-2015, 10:47 AM   #24
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Quote:
Originally Posted by VinceU View Post
DISAGREE WITH SOME OF YOUR POINTS. The aircushion is designed in by Atwood and Suburban otherwise they would tap the tank top for more volume.
I think this is a questionable theory. The air will dissipate top of tank above the bleed valve or not. That is why there has to be a diaphragm in a pressure accumulator tank. Water will absorb most if not all air in just a few days of use so if there is an intention to keep air in a tank, it has to have an accumulator. The hot water outlet and the pressure relief valve in RV water heaters come as close to the top as practical allowing for the way they have to slide in and out for convenient installation and replacement.
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Old 09-06-2015, 11:07 AM   #25
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Originally Posted by dicky1243 View Post
Question? When you hooked up the hose and turned the water did you bleed off the air at the water relief valve if not that is where the air is comming from once that gone should work fine.
DING DING DING This is the correct answer; just open a hot water faucet inside and bleed off air before turnin the water heater on. It also helps to run water thru the hose before connecting to camper, therefore not inducing more air into the system
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Old 09-07-2015, 11:23 AM   #26
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Vince Is Right!!

Dear Vince and Kids,
Please do read my response, thank you for bearing with me. One of the original points made was that that Atwood and Suburban water heaters are designed with an internal air cushion. That is in fact correct, please see page 5 of the Atwood manual here http://www.askforatwood.com/manuals/...S%204.9.09.pdf. There is in fact the procedure described by Vince to reestablish the air cushion written in the manual. So Vince was in fact quite correct!

To re answer the OP question, a small burst of high pressure from a faucet; after the water heater has been first turned on and satisfied; is normal. A drip now and then from the T&P valve is normal in this application (a closed system). Anything else indicates a problem. The rest of my reply is academic, read at your own risk.

The above mentioned manual does also state the air cushion will be absorbed by the water and for a permanent solution to install a diaphragm expansion tank on the cold inlet line. Another permanent solution stated in the manual is a pressure relief valve installed in the cold inlet line set to a lower pressure than the water heater T&P valve. Of the two I would strongly recommend the expansion tank, it will also reduce water pump cycling which will increase the pump's life.

I would like to dissect; literally; the Internet blog channel Vince quoted to illustrate how a little fact can be added to by assumptions and opinion and then spread as fact. I do not have the link to the blog, so I cannot respond to the source. Read on at your own risk, I do not wish to; and it is not to; detract from the fact Vince was quite correct!

Quote:
In other words a P&T valve which is always weeping way not necessarily be bad.
Yes, a T&P valve that is allways leaking *is* bad. It indicates a problem, that can possibly be solved as easily as relieving the water heater over pressure by opening a faucet. The spec sheet f/a Watts 100XL T&P http://media.wattswater.com/ES-10L-100XL.pdf states in part "The combined 2 in 1 T&P relief valve provides the least expensive and proven means for protection against both excessive temperature and pressure emergency conditions." and "This device is designed for emergency safety relief and shall not be used as an operating control." The key words I see are "emergency conditions" and "shall not be used as an operating control". In other words a T&P that is leaking is an emergency condition. Is an emergency condition bad?

Quote:
We know H2O expands when heated so we might then conclude there is always excess pressure in the water tank. This is true…only to a point however.
In a properly operating water heater there is almost never excess pressure. In a water heater that is hot, does not have excess pressure how does it magically get excess pressure with no other input????

Quote:
A properly functioning RV water heater always has an air expansion pocket in the top of the tank. What is an air expansion pocket? It is simply an air pocket, which naturally forms in the water heater tank when it is filled.
This of course we have proven as true, and as Vince stated. In this case this is the grain of truth in the sea of disinformation.

Quote:
As long as this air expansion pocket is of sufficient size, the only time the P&T relief water valve will weep is during the heating cycle.
If the expansion tank, or pocket in this case were of sufficient size the T&P would not drip. I submit a spec sheet from AO Smith http://www.hotwater.com/lit/spec/tanks/aoseb55300.pdf. On page 2 it states in part "Thermal expansion in a closed plumbing system can be damaging, dangerous and costly. Its effects include damage to water heater connections, gas water heater flue tubes, pumps serving washers and dishwashers, leaking faucets, weeping ̋ of water through the water heater T&P Relief Valve, and noisy water hammer in the pipes. A properly sized Expansion Tank eliminates these problems, ".

Quote:
Reintroduce an adequate air expansion pocket and this is how it is done:
. Part of this procedure asks you to open the T&P to drain water from the tank. The spec sheet f/a Watts 100XL T&P http://media.wattswater.com/ES-10L-100XL.pdf states in part "The combined 2 in 1 T&P relief valve provides the least expensive and proven means for protection against both excessive temperature and pressure emergency conditions." and "This device is designed for emergency safety relief and shall not be used as an operating control." The key words I see are "emergency conditions" and "shall not be used as an operating control". The reason for that is the T&P is an automatically operating unit, and if excessively manually operated will prematurely fail. It is designed to cycle a certain amount and beyond that it will start to fail. In this case would you be using the T&P as an operating control? Yes, I realize that the Atwood manual in fact states you should be using the T&P as an operating control. This shows that Atwood in fact does not fully understand how a relief valve operates. It they did an additional valve would be provided to re establish the air cushion/pocket, or *gasp* they would install an expansion tank. But that is the difference between meeting minimum requirements/code and what is good practice. But that is a rant for another day and thread! If you have read this far, thank you for flying with us, happy camping where ever the road leads you!
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