Help with an expansion tank

[Wayne Lippman]

I installed a PRV because my water pressure was 90 psi. It is now 55, but when the water heater comes on with no one using water, the pressure goes up to 80. I take that as a sign I need an expansion tank.

I have a 3/4" cold water line going to a corner of the basement with a threaded faucet on the end of it. I am not sure why it is there; maybe to wash out a sewage ejector pump in the floor near by? Anyhow, it would be really convenient to simply hook the expansion tank to that faucet. Would that do the trick? I was thinking a washing machine hose would be a good choice for the connection, but if there is a better choice...

I have read that they can leak. Are we talking about trickles of water, or massive blow outs. Perhaps the washing machine hose that shuts off if the flow gets too high would be a good choice; does it allow backflow?

What size do I need? 50 gallon tank.

Lowes has two brands; one is rather more expensive than the other; Eastman and AO Smith. I don't want to save $20 and have an avoidable problem, but I don't want to waste $20 if they are the same thing. What do you think?

Your help is appreciated.

 

[Terry]

It comes with a 3/4" pipe thread, not a hose thread.
2.1 gallon works for a 50 gallon water heater.
They normally last about 15 years, and it's better to replace them before they rust through.

 

[Sponsor]

 

[Wayne Lippman]

It is easy enough to go from 3/4" to hose thread, isn't it?

 

[Terry]

It is easy enough to go from 3/4" to hose thread, isn't it?

They are totally different. You can get an adapter from hose to IP, but certainly not hose onto IP. Way different. At least try it in the hardware store so that you understand why not.

Hose thread is a straight thread which seals with a rubber washer. The threads do nothing except to pull it together.

Iron Pipe threads are tapered and the seal is at the threads.

One is a Fox and one is a Hen.

 

[Jadnashua]

FWIW, if it only gets to 80psi, you may have a leak somewhere! Since water and copper piping is not really able to balloon at those pressures, there's either a leak, or some hoses that can balloon to accept the extra volume. Normally, if the system is tight, it gets high enough to cause the T&P valve at the water heater to open at 150psi to relieve the excess volume that's raising the pressure.

 

[Wayne Lippman]

1) With no water being used, the water meter doesn't budge. That probably means I don't have a leak, doesn't it? The pressure can't get over 90psi because the the PRV has a bypass on it. Perhaps the full water pressure had dropped to 80 when I was testing it. I don't know.

2) Won't this fitting connect 3/4" iron pipe to a hose?
https://www.amazon.com/Nelson-855784-1001-Male-Female-Fitting/dp/B0015ASX12/ref=sr_1_5?crid=3O74ANQ3SCAWF&dchild=1&keywords=3/4+npt+to+garden+hose+adapter&qid=1589818399&sprefix=hose+adapter+to+3/4,aps,168&sr=8-5

 

[Terry]

Yes, the "adapter" allows you to do that.

 

[Jeff H Young]

1) With no water being used, the water meter doesn't budge. That probably means I don't have a leak, doesn't it? The pressure can't get over 90psi because the the PRV has a bypass on it. Perhaps the full water pressure had dropped to 80 when I was testing it. I don't know.

2) Won't this fitting connect 3/4" iron pipe to a hose?

Answers 1 no you dont have a leak if meter dosent spin at all. Dont over think this your not supposed to have 150 psi just forget about that.
2 its a 2 dollar part 3/4 inch iron pipe to3/4 inch hosethread adapter .
You can do this its about as simple as it gets . Good luck

 

[Wayne Lippman]

I tried the existing valve. It is frozen and I presume it needs to be replaced. As long as I am doing that, I might was well run pipe from the existing pipe to the expansion tank. I want to put a faucet and shut off valve on it.
The existing pipe is 3/4" copper with a 3/4" IP adapter on it. I can run iron all the way down, or I can remove the adapter and put it on the tank, and run copper down to it. Is one solution better than another; or is it just a matter of whether I'd rather use a torch or wrenches?

 

[Reach4]

The existing pipe is 3/4" copper with a 3/4" IP adapter on it. I can run iron all the way down,

If you mean galvanized pipe, there is no good reason to run that for potable water in a house; it rusts. If you mean IPS (iron pipe size) adapters, then that's fine.

 

[Wayne Lippman]

Yes, I meant galvanized. So I should go to copper; right?

 

[Reach4]

Yes, I meant galvanized. So I should go to copper; right?

Yes. It is not important that you maintain the 3/4 inch over the path. Consider adding a drain valve, since some are worried about whether that constitutes a dead leg. https://terrylove.com/forums/index.php?threads/tet-deadlegs.86420/

The smaller the pipe ID, the more the water gets swapped out routinely. So maybe run the long run with 1/2 or 3/8.

If the galvanized pipes is there already, it may be coated inside with deposits that will prevent significant new rust from happening. But don't add new galvanized.

Regarding calling galvanized pipe iron, steel has a higher percent of iron than cast iron does. Cast iron has a lot of carbon. Making steel is largely burning out a lot of the carbon. It's just not common to call "galvanized pipe" "iron pipe" in the plumbing world.

 

[Jadnashua]

When iron rusts, the iron oxide ends up being a larger volume compound, which exposes more of the underlying iron so that it can rust, too. They don't galvanize the pipe after they cut the threads, either in most cases, which means that they've cut off any protection that may have happened there, and on the end during the initial galvanization process...you do not want to use any iron pipe in potable water systems anywhere. It WILL eventually rust and create problems. The water you get out of the pipe WILL have some dissolved oxygen in it, and it WILL rust anything ferrous.

Way back when, I thought logically that it would be handy to have a valve between the ET and the supply line to make eventual replacement easier...but, I got beat up when I suggested it by some of the pros at the time. You ideally want the ET to be in a location where it can always do its job, regardless of where the thing is placed...that means nothing that can block the flow to OR from it in normal operation in case someone flips a valve they shouldn't, and forgets to move it back. As long as it is not isolated, it will work.

 

[Wayne Lippman]

Expansion tank is in, and seems to be working. I turned the heat to VAC for a few hours and then turned it up much higher than I normally have it. It went from 50psi to about 62. Without the tank it would have gone to 90 so that is correct, isn't it?

Had to solder 14 joints with no leaks; my first in 15 years. I put a valve in because I had a couple I probably would never used for anything else, and a faucet because there was one there originally. And then I figured it out! There was a length of hose there, and I thought it was for washing out the sewage ejector pit near by; but then I saw the hose had female hose threads on both sides. Someone had done exactly what I was thinking of... connecting it to a tank with a washing machine hose! Previous owner was incredibly cheap; it probably needed to be replaced and he just left it out.

 

[Jadnashua]

Well, normally, the pressure doesn't actually go up much IF the tank is properly sized and precharged. 12# is certainly better than a 40# increase, but I'd have expected it to be less than that.

 

[Wayne Lippman]

Well, normally, the pressure doesn't actually go up much IF the tank is properly sized and precharged. 12# is certainly better than a 40# increase, but I'd have expected it to be less than that.

It might have been high because I set the thermostat to a much higher setting than I normally use, so the water expanded more than usual.

But 62 isn't likely to cause any problems is it? Presumably most of my neighbors have 90psi all the time.

 

[Reach4]

It might have been high because I set the thermostat to a much higher setting than I normally use, so the water expanded more than usual.

But 62 isn't likely to cause any problems is it? Presumably most of my neighbors have 90psi all the time.

No problem. Set the air precharge to 55 psi -- the PRV setting, or maybe 56 or 57.

The temperature of the incoming water comes into effect if you actually calculate. I would go with the 4.5 gallon unit to give margin, but the 2 gallon size is OK according to the sizing charts. Your water is probably fairly cold. So your water will expand more than it would in a warmer area.

 

[Jadnashua]

This time of year in upstate NY, the water usually isn't all that cold unless you have a deep well, which you don't since you're dealing with a public utility. Grew up in Spencerport, NY, so have a feel for that area! The delta-T in the middle of winter will be greater. Where I live, I've actually measured it at 33-degrees after a cold spell.

 

[Jeff H Young]

This solved yet? what are you going to try next?