Lingering return pipe noise ... poor venting?

Saldanah

We have a two-pipe steam system, and one return riser has persistent sharp clicking and occasional banging mid-cycle, along with gushing sounds and sluggish condensate flow. When placing an ear to the pipe, it feels like a sucking motion.

We can’t access the full length of this pipe as it heads to the boiler but don’t suspect any bad traps. Hoffman vents are installed on the main return line in the boiler room, and the F&T traps before the condensate tank were recently replaced. There are no known pitch issues.

Could poor venting be causing the noise and these symptoms or is it something else? Currently, the vent is closed because opening it seems to worsen the problem—possibly indicating venting is a factor? Should we open and throttle the vent? If so, what’s the recommended adjustment? At more than 1/3 open, we hear air hissing. What’s the right balance to reduce noise while ensuring proper venting?

Thank you.

Jamie Hall

Whoa. OK. Two pipe steam system. How are the traps on the radiators? Are they functioning properly? It can be a little hard to tell, but with the heating system going and the radiators full — hot across — the outlet from the trap should be warm to hot, but noticeably cooler (at least 5 degrees cooler) than the inlet from the radiator to the trap.

Additionally, all the dry returns — return lines above the boiler water line — may be warm, but none of them should be hot.

Check the rest of the piping. If there any low level return lines — near of at floor level — they must be below (preferably at least two to three feet below) the water level in your condensate tank. If not, any drips (pipes coming down from a steam main to one of these pipes) must have a trap on it (might be an F&T, but could be thermostatic) and that trap needs to be working.

Saldanah

Thank you. We had the two F&T traps in the boiler room leading up to the condensate tank replaced (bought the repair kits from Woody Tunstall). Wonder if there is a way to quality-check them. We have a bypass valve for the F&T but that is likely just to allow repairing them.

The vent for the returns is in the boiler room as well. Manual. I am trying to throttle the vent to see if that helps with the jerky movement of condensate in one return pipe in an apartment (presumably air pockets). A number of risers that are exposed return pipes passing through that apartment get very hot, so steam is entering them?

At this point we are focusing on two accessible components — the F&T traps and the main return vent. Unclear if either of them is causing the symptoms — steam in return pipes and the clicking and jerky movement of the condensate coming down those pipes. The pitch and steam pressure have been corrected/adjusted.

Jamie Hall

Steam in return pipes will cause all kinds of mischief. Some expected, some not. Your very first step is going to be to find out where that steam is coming from. You likely have several traps here and there which are failed, and you need to find all of them and repair them before you look at anything else.

The second place to look for trouble in your system is any drips where condensate can come from a steam main down to a wet return pipe. Those drips must have fundtioning traps on them — most conventionally F&T, and you need to check size — they're probably too big.

So long as you have steam coming out of the condensate receiver vent, you have a problem — which must be resolved.

Now. I'm puzzled by your comment about the vent for the returns. If these really are dry returns, that vent should be always open, and steam should never get into them. An automatic vent does need to be there, but it should never close. If steam is getting into those dry returns, go back to the beginning here and find the villains. Could be either the device traps or those drips I mentioned.

I might add that both of the things you are complaining (rightly!) about are almost certainly caused by either bad traps or those drips.

Saldanah

Thanks, point taken about tracing the line and accounting for all traps. Unfortunately, some length of the pipes is wrapped in asbestos and concealed in the first floor ceiling.

I am attaching pictures from the boiler room showing the vent on the main return … this is above the boiler water line. And two F&T traps that are below the water line and next to the condensate tank.

Jamie Hall

Two nice Hoffman vents there. Why on earth are they valved off? If that dry return has steam in it, fix that problem — don't bury it with that valve.

Saldanah

well, believe it or not, when those vents are full open, the noise is worse. as i am opening the valve it begins hissing at the 1/3rd open point. Wonder if I should throttle the vent — how do I know where to stop?

Saldanah

There is steam entering the returns. Question is where are the bad traps. The steam rises from below so the traps that are malfunctioning are below the return lines that are getting super hot.

Is it possible that the f&t traps are the culprit (they are in the boiler room in the basement)? If the f&t traps are sending steam through to the condensate tank, the pressure could build up and could be pushing steam back out into the return lines and be causing the banging?

If I see that the downstream pipe connecting the f&t traps to the condensate tank is steaming hot, can I conclude the f&t traps are passing steam through and are the likely culprit? That section of pipe is insulated but I can probably open up a segment to check the temperature if that is worth doing.

We are seeing if the venting can help, but if the f&t traps are not functioning well, then perhaps that is what needs to be resolved?

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1830409#Comment_1830409

I do believe it. Really. As I've said above, no you should not throttle the vents. That pipe should be at atmospheric pressure at all times, and never, ever, ever have steam or pressure in it.

Find the actual problem traps or cross connection and fix the problem. Don't keep trying to put a bandaid on it.

Saldanah

Understood. I need to figure out if the f&t traps are working.