Everyone's favorite topic - gurgling pipes

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Old 10-17-18, 10:31 AM
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Everyone's favorite topic - gurgling pipes

Thanks in advance for any ideas the group may have. I am dealing with gurgling in a hot water stand pipe for baseboard heat. I thought it was air trapped at the top, so I had a bleeder valve installed at the top of the stand pipe this summer. But there's no air in the pipe, yet the issue persists. I have tried flushing the system; it was also flushed by pros when the bleeder was installed a couple months ago.

Most interesting to me is that the noise is very cyclical; one big gurgle every 4-5 seconds, like clockwork. It sounds like a wave within a horizontal pipe. Silence in between. I believe the noise may be reverberating up the pipe from the basement.

For some reason they left a 1 1/2" pipe for the stand pipe, where it goes down 2 floors to the basement and bends 90į for several feet before reducing back to 3/4".

I have lots of theories - would like your opinion. Perhaps the upper cross section of the horizontal larger diameter pipe is filled with air, and the air can't get pushed out through the reducer into the 3/4" pipe. That would create a wave/gurgling sound if the air is sloshing around.

Perhaps the sudden increase in diameter is allowing air to form within the vertical standpipe.

But I am no expert.

Any theories, or how to test? Worst case I drain the system and replace the 1 1/2" standpipe with 3/4" copper but I'd hate to go through that expense on my single theory.
 
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Old 10-17-18, 01:31 PM
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What is the system pressure and temperature? What automatic air removal device(s) are installed?
 
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Old 10-17-18, 06:07 PM
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180į, 12 psi. There are no automatic air removal devices - the system has an expansion tank.
 
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Old 10-18-18, 05:20 AM
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What type of expansion tank do you have? A bladder type (looks a bit like a propane tank for a BBQ grill)? Or a conventional, steel tank - probably hangs from the ceiling joists in your basement?

When you say "stand pipe," is it a riser carrying water? When did this problem start? Is it relatively new? Don't rip out piping yet - that probably isn't called for. Please post some photo's of your system.

In the meantime, temporarily jack up the system pressure to 20 psi, and see if the noise goes away.
 
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Old 10-19-18, 06:35 AM
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Conventional steel tank. Yes, it's the riser from basement to the 2nd floor loop. They left a 1 1/2" riser in place and connected 3/4" copper to both ends. Hopefully this weekend I can play with the pressure and see if that eliminates some air. I'll post back with results.
 
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Old 10-20-18, 02:39 PM
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Updates

A few updates. Thoughts, comments?

1) the pressure dial on the boiler reads 12 psi (as does the label on the pressure reducing valve). But, I hooked up a pressure gauge to the drainage bib and it read 18 psi. Is it possible the boiler gauge is off by that much,? If so, I don't want to follow the boiler's gauge and overfill and accidentally blow the 30 psi release valve. Thoughts?

2) The house has 4 loops (all one zone). I closed the other 3 to increase flow through the problem pipe. This appeared to work. 5 Min of flushing and the gurgling sound went away, and stayed away after I opened all the loops again.

Time will tell if this solved the issue. In theory it makes sense. If I have a section of 1 1/2" pipe, that section is only getting 1/4 the water velocity of the 3/4" pipes. So closing the loops drastically increased water velocity and cleared the air. But, how is air getting stuck in the basement in the first place? You'd think it would work back up to the top floor bleeder valve, but it isn't. Some shots below.

This is where the top floor 3/4" turns down and into 1 1/2". No air comes from the bleeder valve.
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This is the basement where the 1 1/2" (now horizontal) reduces back to 3/4". My theory is that air is getting stuck in the top 1/2 of the larger pipe, and is unable to clear at lower velocities. The question is how quickly it will fill up with air again, and how often I'll have to isolate that loop to clear the air.
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Old 10-20-18, 02:59 PM
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Yes, it is possible that the boiler pressure gauge is off by that much. But, it's just as possible that the second gauge you connected to the drain valve is off. I wouldn't worry to much about "blowing" the relief valve - it will just lift slightly before it opens fully - at or close to 30 psi. It will reclose on its own. But, it would be best if the relief valve doesn't lift, unless you are purposely doing it as preventative maintenance.

I don't put much stock in your theory about the change of pipe sizes leading to air in the lines. The air would first have to come from somewhere - and that would be the problem, not the pipe sizes.
 
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Old 10-20-18, 04:48 PM
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I completely agree with gil. The difference in pipe sizes has no effect or cause air to get into a closed loop system.

There are only a couple of ways for air to get into a system. One is by feeding fresh water, which brings air with it, into your system or if you have a leak which causes constant feeding to replace what is lost or sucking in air from a defective vent when the pump comes on.

Since you don't seem to have any leaks my thought is your air is getting in from the way you are bleeding the system.

The short version is when you bleed your system you must do it with high pressure of between 25-28 PSI and maintain that pressure until all the air is out and when you are done you end up with that high pressure still in the boiler.

You then drain water out slowly until your desired pressure of around 18 PSI is acquired.

You do this so you end up with a higher pressure than the feed valve is set for and it will not introduce any more water and air after your done bleeding.

If your system is bled properly there is no way for air to get back in and as long as your system isn't drained you'll have no more air problems.

Hope this helps a little.
 
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Old 10-21-18, 08:00 AM
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Well, it didn't take long for the sound to come back so more air got there somehow.

I have an expansion tank, not a bladder tank, so there is always air in the system. I was under the impression that hot water holds more air than cold water, so bubbles form when the system is off and cools? But then when the pump turns back on, those bubbles are quickly sent back to the boiler (and into expansion tank) and the cycle repeats. There's no automatic air removal because the tank would get waterlogged.

Often when the pump turns on for the first time in hours/days I hear bubbles in the loops for about 30 seconds until they are cleared. The system is then silent, except for this one location. Air is just getting stuck in this one location time and again.

To your point, moving to a bladder-type system could resolve the issue.

If increasing pressure solves the issue, would you recommend leaving it at 20+ psi permanently?
 
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Old 10-21-18, 08:16 AM
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You are correct - a conventional expansion tank, unlike a bladder type, should not have automatic air eliminators on the system. But, a conventional tank needs to have means to return air from the system back into the tank. (Each time the system cools down, water from the tank flows from the tank into the system, and that water carries air.)

A common device to return air to the tank is a Bell & Gossett boiler fitting (which you can Google), along with an upward sloping pipe connecting the fitting to the bottom of the tank. If you post photos of your boiler, exp tank, and piping, we can help you verify what you have.
 
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Old 10-21-18, 08:44 AM
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I do not have access to photos at the moment, but I can tell you my boiler is attached to the expansion tank via upward sloping pipes. There is not an airtrol device in the tank but I do not have a problem getting air into the expansion tank from the boiler. In all the other loops, any released air gets pushed to the boiler and flows into the expansion tank. After initial start up, those loops all run silent. It appears that released air in this problem loop is getting stuck, and creating noise. I do not know why it is not getting pushed back to the boiler like all of the others. it appears that released air in this problem loop is getting stuck, and creating noise.

that was my original theory about the larger diameter riser pipe being the problem. Velocities would drop significantly in that section, making it difficult to push the air down to the basement back to the expansion tank. That doesnít make entire sense, however, because there isnít any air at the manual bleeder valve at the top of the riser which is where it would get trapped.

So here I am..... Iíll trying upping the pressure but would you leave it at 20psi(if that works)? Because I can easily clear the air by isolating that loop, but the Released air from cool down gets stuck there again at the next start up.
 
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Old 10-21-18, 08:52 AM
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Found photos

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Old 10-21-18, 10:32 AM
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From what I see in the photos, I think the piping should return the air in the system back to the tank. If you just leave the pressure at 20 psi, does that solve the noise issue? Running the system at 20 psi shouldn't hurt anything.
 
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Old 10-21-18, 10:40 AM
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After looking at your pics I have a couple of thoughts.

Your expansion tank is fed from an independent line instead of coming off the supply line and ordinarily an air scoop.

You have given the air 2 directions to go. What makes you think it would pick the tank line instead of the supply which is circulated water pressurized by the pump and back into the system.

Air, like water is going to take the path of least resistance.

If you repiped your tank to the supply line, attached to an air scoop and just used that other port for your relief valve the air would have no choice, along with the expanded water, but to go up that line into the tank.

Another thing to make sure of is that your tank is not water logged. The more you let fresh water in to bleed the system the more water is going to get into that tank and eventually become water logged and must be drained and refilled properly to provide that air cushion on top.

When you drain that tank it must be drained completely and not partially or it will be worse than not draining it at all.

Yes, I would run that system at 20 PSI all the time.

Hope this helps a little.
 
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Old 10-21-18, 10:41 AM
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I was under the impression that hot water holds more air than cold water,
No, it's the other way around. The solubility of air in water is lower at higher temps. At 212 degF and at atmospheric pressure, the solubility of air is zero - which is why some deaerators operate at the boiling point.
 
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Old 10-21-18, 10:55 AM
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I noticed after my last post that you mentioned your pressure was 12 PSI at 180 deg.

When a boiler heats up to temp your pressure rises at least a couple of pounds or sometimes more but the point is if your hot pressure is 12 what is your cold pressure. Is it below 12 PSI.

If so, since your feed valve is factory set at 12-15 PSI, as soon as it drops below 12 it is opening back up letting fresh water in that also brings air with it creating that vicious cycle. Then you bleed again and if not bleeding properly with high pressure you are introducing even more air.

Try 20 PSI cold pressure and your air problems might disappear.
 
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Old 10-21-18, 03:29 PM
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It may be 12 psi cold and 14 psi hot - the gauge is not very easy to read on the boiler and it isn't very accurate. I'd bet it's at 12 psi cold. I don't think more water is coming in; there is no known leak.

Is increasing pressure to 18 psi as simple as manually opening the pressure reducing valve until the system hits 18 psi and closing it?
 
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Old 10-21-18, 03:42 PM
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Yes, that will do it. Don't be afraid to go to 20. That's what I run mine at and now Taco is even recommending that with there pumps to help alleviate cavitation.
 
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Old 10-21-18, 03:53 PM
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Sounds good. There's still the question of which gauge is more accurate - 18 psi on the boiler gauge will look like 23-24 psi on the Winston one attached to the drain valve. I'm not that concerned about over pressurizing except for the release doesn't go into the sump - just onto the floor. :-/ Hopefully any leaks are smaller than a bucket.

Backing up a couple posts to answers spott's questions; the high point in the boiler itself connects to the pipe going to the expansion tank. You are correct that air could make its way back into the supply pipe (which is lower), but I haven't had that problem. I'll hear air when the system starts up but very rarely when it's running. So I think the air is getting into the tank - I think air is just getting stuck in this one loop. To your point, however, an air scoop would do a better job of this. If I cannot solve the issue with pressure I can always add an air scoop, or just go to a bladder tank and automatic air removal. I assume that would solve the problem since all air is eventually permanently eliminated from the system. Time will tell. I'll report back after I get this pressure test done.
 
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Old 10-21-18, 04:06 PM
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When two gauges disagree, and they each display readings that are within the range of reason, there is no logical way to identify which is wrong, or even if both are wrong. You need a third gauge. I have two different pressure gauges on my system, and they both agree. (Right now, one gauge reads 15 psi and the other reads 14.) Be aware that any elevation differences between two gauges will cause a difference - of about 0.5 psi per ft. (That may partially explain a higher reading on the gauge connected to your boiler drain valve.) Also, if the circulator pump is running, that can throw everything into a cocked hat.

Older bourdon tube pressure gauges, I think, may tend to indicate high - maybe the tube mechanically creeps a bit over time - but that should show up in the gauge not zeroing out. So, using that theory, maybe lean toward the newer gauge?
 

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Old 10-21-18, 05:23 PM
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Originally Posted by spott View Post
Yes, that will do it. Don't be afraid to go to 20. That's what I run mine at and now Taco is even recommending that with there pumps to help alleviate cavitation.
Interesting.

I wonder what's behind Taco's 20-psi guidance? Maybe Taco pumps are a bit more at risk for cavitation, at least compared to the old, bullet-proof B&G 3-piece pumps?

Taco wet-rotor pumps have higher rpm than the old 3-piece pumps - motor synchronous speed of 3600 vs. 1800 rpm. And nylon or plastic impeller, vs. bronze?

I've had no problem with either the 3-piece or wet-rotor pumps that I've used. Cavitation would be easily identified - it sounds like pumping rocks as the fluid at the impeller vaporizes and collapses. Jacking up the system pressure would certainly alleviate that.
 
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Old 10-21-18, 05:30 PM
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g,
It is with the wet-rotor pumps they recommend it but I didn't know if he knew the term wet-rotor meant and didn't want to confuse anyone.

Something with design I guess compared to the old 3 piece that makes it more prone to cavitation.
 
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Old 10-21-18, 06:41 PM
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Well it's been brought up to 22 psi on the newer Winters gauge and reads 15 psi on the boiler gauge. I should note that there's not much pressure change from cold to hot, so I don't think the system is waterlogged by any means. Perhaps I'll buy a 3rd gauge in the mean time. I imagine there is a big difference between 15 and 22 psi as it relates to my issue. If the solution works it will likely be a day or so before it's proven out and I come back to post. Thanks!
 
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Old 11-10-18, 06:35 PM
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Just an update - I have been watching the pressure to ensure there is no leak. It has held steady 16-18 psi on the gauge on the boiler. So far, the gurgling noise has been eliminated at this location.

It appears this is the solution. thank you all for the help.
 
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Old 11-11-18, 10:30 AM
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Thank you for the update.
 
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