Water heater relief valve

[Tom]

This is a belated follow up to an ealier thread in our prior location.

I'd reported the relief valve on the hot water tank letting out water quite frequently when the water got hot. I received several useful responses, including re-establishing a head of air, manually opening the relief valve, and replacing the valve. This was one of those things I didn't get around to for a long time. I recently re-established the head of air and manually opened and closed the relief valve. The result was a continuous stream of water from the valve when the water got hot. This led me to believe the valve was defective, i.e. it wasn't seating correctly, which was one of the original suggestions.

I couldn't locate a local source for the identical valve and ended up ordering one from a local store. The valve arrived overnight, specifically for my Attwood water heater. It's even the same part number. But the old valve has "210o, 75psi" on it whereas the new one has "210o, 150psi" on it. That's the exact same thing I turned down at an RV repair place yesterday as being the "wrong" valve.

Does anyone know why there might be two different pressure specs?

FWIW this water heater is 220V (no propane).

 

[Karl]

Tom,

I'm assuming your water is not getting near-boiling hot, which would be a problem with the temp. control and not the valve, and that you have not 'lost you head'.

The relief valve has two purposes: relieve excess pressure, and open when the water's too hot (letting in cooler water). Most are rated at 210 deg.F, but the pressure rating is based on the maximum safe operating pressure of the tank and associated plumbing. Rheem advises that you NEVER replace a 75psi relief valve with one of higher rating (150 in your case). It might be o.k. if you have a pressure limiting device on your city water connection, and your onboard pump certainly wouldn't exceed 75psi anyway. With the higher pressure valve, if something went terribly wrong, you could end up with a very expensive, multi-wheeled swimming pool.

 

[Tom]

Thanks Karl.

I'm assuming your water is not getting near-boiling hot

I'm still able to wash dishes and take a shower with it, i.e. it's hot, but I have to mix some cold water, but I don't believe it's near boiling.

that you have not 'lost you head'

I had previously lost it, but replaced it after your prior explanation of how to do that.

It might be o.k. if you have a pressure limiting device on your city water connection, and your onboard pump certainly wouldn't exceed 75psi anyway.

This is a situation where a city connection is never used. Any idea what the typical pressure is with on-board pumps? They're just like typical Shure RV pumps (2 in parallel to provide greater volume - more sinks and showers).

you could end up with a very expensive, multi-wheeled swimming pool.

Since it's below decks on the boat, it would drain into one of the bilges and be pumped overboard.

I might install it as a temporary measure, but will call Attwood given that it has the same valve number as the old (75 psi) one. I was careful to specify the temp and pressure ratings when I had the guy order it.

Thanks again.

 

[Ned]

I doubt your onboard pump will put out more than about 40psi.

 

[Tom]

I just called Atwood tech support - very polite and efficient - and here's the scoop:

The 75 psi relief valve is a requirement for Europe, or at least some European countries. My tank is rated at 350 psi and the 150 psi relief valve is the correct valve for this tank in the USA.

 

[Ron]

That is good news.  Hope the new relief valve corrects the anomaly.

 

[Tom]

Me too Ron    I just installed the new valve and hooked up the water line and drain hose. Heater is on, and we'll see what happens in a short while. My bod doesn't go into these tight quarters as easily as it used to.

 

[Tom]

Ned, I suspect you're right, although I don't know exactly what the pressure is.

 

[Ron]

I doubt your onboard pump will put out more than about 40psi.

Unless he has an Aqua Jet water pump like we do that provides 5.5 Gal per minute @ 60 PSI.

 

[Ned]

Our Aquajet sure doesn't put out 60psi.  It's the model YOU recommended

 

[Ron]

Per the Aquatec information at http://www.aquatec.com/new/products_files/specialty/rv.htm  The OEM version Aquajet (which we have) Patented 5-valve design delivers up to twice the flow (5 gpm) and pressure (60 psi) of traditional RV pumps.  The ES or aftermarket version version Delivers same high pressure (60 psi) as the original Aquajet RV, but at a reduced flow rate (3.5 gpm).  So whether you have the OEM version or the aftermarket version you should be able to get 60 psi from it. Unless you set the pressure setting lower.

IMHO it is the best RV water pump available.

 

[Ned]

The pump works ok, but it doesn't put out anything near 60psi and isn't adjustable as far as I know.? It also pulses, especially at low flow rates, but it's better than no water at all

The model no. is Aquatec Aquajet model ES3.5.

 

[Ron]

That is the aftermarket version whci is an excellent pump.  The only reason we got the OEM version is that we bought ours before the ES version became available.  The I believe pressure is adjustable and instructions are included in the installation guide.

 

[John From Detroit]

One thing that can happen.. In some instalations they put a check valve in the INLET line to the how water heater, This is to prevent HOT water from backing up into the cold water lines when you loose pressure in the system (which is very common, espically when you are on the pump)

Well, water EXPANDS as it gets hot Just like when it freezes (Water at the freezing point is an anamoly in the way things work, which is normally they get bigger the hotter they get) the tank expands as well, but not as fast, this causes an increase in pressure in the tank and the venting you describe.

The solution is to use the higher pressure valve you received in the post.

It's that simple

 

[Ned]

Being curious about the performance of my pump, I got the performance data from Aquajet:

PERFORMANCE DATA
DISCHARGE PRESSURE FLOW CURRENT
(PSI) (BAR) (GPM) (LPM) (AMPS)
65 4.4 0.60 2.27 6.50
60 4.0 0.70 2.65 6.50
50 3.4 1.00 3.78 6.50
40 2.7 1.60 6.05 6.50
30 2.0 2.30 8.70 6.50
20 1.4 2.70 10.22 5.80
10 0.7 3.00 11.35 4.60
OPEN OPEN 3.40 12.87 3.60

It appears that I can get up to 65 psi but at a flow rate of only .6gpm.? For a decent shower at 2.7gpm it will only produce 20 psi.  Of course, if I can get the water I need, it really doesn't matter, but a high pressure shower at times would be nice .  The after market pump isn't adjustable either, it's factory set for draw a maximum of 6.5 amps (as seen in the above chart), thus limiting the available pressure and flow rate.

Thus more than most people ever wanted to know about a water pump

 

[Tom]

After a couple of heat up and cool down cycles, it looks like the new relief valve did the trick. However, as mentioned earlier, I'd also lost the head of air in the hot water tank and this was replaced using a combination of Karl and Don's methods.

As you see from the photo, it wasn't easy getting to the valve or the overflow hose.

 

[Ron]

Heck Tom that would have been a piece of cake to do that job            for an experienced aircraft mechanic. ;D ;D

 

[Tom]

LOL Ron, I could fit when I was 50 lbs lighter.