Expansion tank failed, but is now fine?

[SephYuyX]

I had to solder on a ball valve at one of the lower points of my house, and even after purging, draining the water heater, and waiting three hours, water was still coming out.

I used an air compressor to blow water back up stream (had all faucets open, and used at a low psi), and that gave me about ~5 minutes of time until water started coming back out at the solder point.

Whether that was a smart or dumb move is debatable, but it worked!

I was able to successfully complete the job, but noticed erratic pressure behavior at the faucets a week later. I checked the expansion tank and it had no PSI, but also no water come out.

I filled the tank back up to match the water heater PSI, and has maintained PSI with the faucet pressure fine for over a week now.

How is this possible?

How was the expansion tank able to "fail" and displace all of that air without busting the diaphragm? The air couldn't escape through the nipple, right?

Should I play it safe and replace the tank, or just see how it goes?

 

[Tuttles Revenge]

Whenever I visit any clients home and they have an expansion tank, I always perform a basic Thunk test.. If the expansion tank Thunks on both sides.. its dead. If it thunks on the water side but rings on the air side, its good, but may need maintenance. If the diaphragm has busted it will be thunk thunk.

They're also not incredibly expensive nor difficult to replace generally. So there is that.

 

[Sponsor]

 

[SephYuyX]

I did attempt that, and it does sound more thunky than tinky (from my remembrance of when first installed), but that would be even more confusing of how it's still measuring the proper 60 PSI lol.

 

[Reach4]

but that would be even more confusing of how it's still measuring the proper 60 PSI lol.

To measure air precharge, you want the water pressure to be zero.

If you read 60 psi of air when the water pressure is zero, that would be significant.

 

[SephYuyX]

Good point.. I did charge it when water pressure was 0, but did not lower the pressure when testing. Will have to try that. Thanks.

 

[Reach4]

I had to solder on a ball valve at one of the lower points of my house, and even after purging, draining the water heater, and waiting three hours, water was still coming out.

It is possible that water was siphoning out of the WH. You should have turned off the WH, and closed the valve feeding the WH.

If that pipe you were working on was a hot pipe, you should have drained the WH. Remember to have the WH off unless the WH is full of water.

 

[SephYuyX]

I had the WH off, closed off at cold, and drained.

 

[SephYuyX]

It's been over a week now, and decided to give the PSI a check.

Emptied the tank a bit to relieve pressure, power off, cold closed, hot facet open with nothing coming out.

60PSI, not a bit of difference.

I know the tank was good before the project, because afterwards I noticed the erratic pressure behavior in the house, and it went away when filling the tank back up with air.

I don't quite understand how the tank could fail to let the air out of it, but still be able to hold pressure.

Oh well, guess I'll just march on and see how it goes in the future. Maybe I'll give it a month and check again.

 

[Reach4]

Oh well, guess I'll just march on and see how it goes in the future. Maybe I'll give it a month and check again.

Good plan.

Put a valve cap, such as one made for cars, on the stem. Supposedly the cap is the primary seal, rather than the valve.

Did a curious child have access to that valve?

 

[Jadnashua]

The Schrader valve is not a perfect air seal all of the time, and a good cap should keep the air in the tank, but not if it was loose, or cracked (if plastic). The better caps have an O-ring, but over time, those can fail, too. If you didn't see any water when you opened that valve, the bladder tank should be okay.

If you have a PRV, and it's wearing some internally, when you shut water off, drain things, then turn it on, that surge of water in the empty pipes can loosen some crud on the insides of the pipes, and that could mess with the seals in the PRV, which might then show erratic pressure if they can't get cleaned off with the flow.