Large Steam system - condensate return problems

TBrown

I have been asked by a local university to investigate condensate problems in a residence hall. Original building and steam radiators still in operation - about 60 years old. About 5 years ago, they replaced the condensate piping. They are telling me it worked for about a year after piping replacement, and then they started having problems getting condensate back. Their solution is to open the condensate line and let it vent to atmosphere, instead of returning to the flash tank that then drains into a condensate pump. It appears they are simply allowing steam into the condensate return system. So they have a constant vapor cloud outside the basement mechanical room where it vents.

Steam is supplied from a central campus utility, delivered to the building at 60 psig. PRV reduces the pressure to 8 psig at the building.

Radiators have thermostatic traps. Some have original manual valves, while others have thermostatic valves on the supply side.

Original design incorporated a vacuum pump, but currently there is only a gravity return to a condensate receiver/pump - no vacuum pump.

Facility is a two story building. Steam and condensate run horizontally below radiators on each level - in a crawl tunnel below the first floor, and above first floor ceiling to serve the second floor. All EOM's and risers are trapped with bucket traps. All condensate eventually makes it back to the piping in the tunnel, and back to the flash tank / condensate receiver/pump in the basement.

I have crawled the tunnels and nothing appears to be wrong with the piping. In fact, the installation is practically as per original design drawings.

They are having problems in two areas of the first floor. No problems on the second floor. Problems are identified by radiators not heating - so they appear to be holding up condensate.

My suspicion is the thermostatic traps are bad in several locations. An infrared thermometer indicates several thermostatic traps with the same high temperature on both sides of the trap - about 195 deg F.

It is very difficult to replace the inline pattern thermostatic traps the way they were originally installed - so quickly replacing a trap is not possible. The process actually requires shutting down a portion of the building and completely removing the radiator to replace the trap - about a 2-3 hour process per radiator.

I have considered simply installing another thermostatic trap downstream of the failed trap, thinking that a bad trap is passing steam anyway, so another trap in series may work.

Would bad traps cause the problems I am seeing? When they open up the return line to atmosphere, I am having trouble understanding what is happening that results in the system to begin working again (or I should say heating again - it's obviously not working).

Hope this is not too long winded - just trying to present what I know about the system.

retiredguy

You have asked lot of questions about this system so let me in-turn ask a few also. #1), Is the vacuum pump still piped into the system and if it is what part of it are they utilizing? If it is still in the system it should be repaired and put back into service. #2), If the temperature on the discharge of those thermostatic traps is 195F why do you think they are bad. The temperature through the traps should be below the steam temperature and "NO" you can not add a 2nd trap after the first. You should be able to rebuild or repair those traps in place. #3), Has the piping system been changed recently that may add to the condensate not returning? #4), Has this system been up graded in any way say, by the installation of zone valves or any new type temperature controls. I would be very careful on this job since many universities were always looking for the quick or cheap fix. There a lot of good steam guys on this site that may be able to help but a lot more information is needed and also, where are you located?

Jamie Hall

I suspect that your initial suspicion is entirely correct. There should never, ever, be steam in the condensate piping, never mind making it to the condensate receiver. And yes, steam in a condensate line will quite cheerfully reduce or stop completely heat in other radiation connected to the line.

However, this may not be your only problem. As @retiredguy asked, are there any zone valves -- new or original -- on the piping, either on the steam mains or the condensate lines or, heaven forbid, on both? If there are any on the steam side, they must, without exception, be dripped (probably through traps) to the condensate line on both sides of the valve. This is often overlooked. There is also the minor detail of venting air at such a valve. Although that will hurt mostly on startup, it's a potential problem.

On one thing I'm afraid I differ slightly with @retiredguy -- if the temperature of the pipe on both sides of a trap is the same, it is very likely that it is passing steam. Now it could also be passing a lot of very hot condensate, but I'd be very suspicious of it.

Would it be possible to post a photo of a typical inline trap? If you could, it is likely that one of the more experienced heads here -- @Steamhead or @Gordo or @EzzyT or @clammy may have experience with them, and know how to repair them without taking the whole thing apart.

Steamhead

TBrown said:

....Steam is supplied from a central campus utility, delivered to the building at 60 psig. PRV reduces the pressure to 8 psig at the building.

That's too high. Get the pressure down to 2 PSI and you shouldn't need the flash tank.

Also- bucket traps can blow steam if they're not properly primed, and they don't handle air venting well. I'd switch them out to F&T traps.

JUGHNE

I just finished, hopefully, a job with the same problems.
Steam pouring out of the return, into boiler room, with large fan to blow it out the window. Steam was set up to about 7 PSI. Now down to 3 PSI and possibly lower next season.
Small private school.

It had bucket traps for a couple of the EOM's.
No one knew they existed in this building.

As many buildings go that have maint people, they don't know that they don't know.

Someone told me about bucket traps and repeated the same thing that Steamhead said. Not good for EOM and might need priming every season.

Changing all the EOM's to new F&T fixed the steam problem.
However we also changed all emitter traps, as some were original from 1951 and no work had been done on the system for at least 20 years.

We did remove the convectors to get under them to the traps.
These came off simply and maint man washed them and helped for the R&R.

I have a recent posting about "Amy school steam repairs".
Some pictures of new F&T with air venting added on there.

Post some pictures of the problem units with limited access to the traps, please.

Steamhead

JUGHNE said:

.......Someone told me about bucket traps and repeated the same thing that Steamhead said. Not good for EOM and might need priming every season.

I got this from Lost Art, at the end of Chapter 10. Thank @DanHolohan .

JUGHNE

That yes, and also my wholesale supplier said not good for heating, that you might use them if you were making dog food or such.
He thought they would have to be primed every season.

Once they were replaced with F&T's the steam stopped flowing out of the pump vent pipe. The rest of the traps were just changed as PM.

JUGHNE

I took one of the Armstrong 800 bucket traps apart. It looked OK as far as I could tell. Nothing broken and all parts moved. The small seat and ball seal was worn.
It is obvious that this would not vent much air.

So down the rabbit hole of Utubes of bucket traps. (why? I will probably never see one again.....IDK)
One thing pointed out was if prime was lost they would blow steam by.
But it was mentioned that if you valve off the discharge and wait for condensate to fill the trap, it would then be primed.

OP said that system worked for the first year....maybe they then lost the prime.

Simple test would be to valve off the discharge and they might prime.
Or shut down and there must be a plug to add water for prime.

This would possibly eliminate these as the steam blow by.

Perhaps narrow down the problem.

Steamhead

If it were me, I'd just change them to F&Ts. Keeps call-backs down.

JUGHNE

But if priming fixed the problem then go for the F&T's.
That would narrow down the culprits.

If F&T's were installed and the blow by persisted that wouldn't look good.

EBEBRATT-Ed

And if it was designed to use a vacuum pump (as others have mentioned) the original piping is likely too small to run without it

Pumpguy

While you're working on this problem, you might also look for the presence and function of equalizer lines downstream of the zone valves.

When the zone valve closes and the downstream steam condenses, a high induced vacuum is formed. When this occurs, the check valve or thermostatic trap opens equalizing the pressure and allowing the condensate to flow downstream by gravity.

The attached file shows the piping arrangement.

TBrown

Thanks to all of you - lot's of good discussion and things to consider and chase down.
Sorry for the delay in responding - I just got time to get back to this forum to review the comments.

Response to the some of the comments / questions that were raised:
1. The only "zone" valves in the steam or condensate piping are in the main mechanical room. They are all open. Really these are manual zone isolation valves - for service.
2. Only piping upgrades have been replacing the condensate return piping. As indicated, it appears to be installed as per original design.
3. Some radiators do have thermostatic supply valves. Others still have manual valves.

From the discussion, it appears the first and simplest thing to address is the bucket traps being used for EOM and drip traps.

The relatively high steam pressure (8 psig) was also something that we can easily address. This also was a flag to me, but thanks for confirming.

I do not currently have a photo of the radiator traps, but the are inline traps installed below the convectors with no unions - that is what makes them so difficult to replace.

Unfortunately we are nearing the end of heating season here in the Texas Panhandle, so may not see any results until next fall (although we did have 6 inches of snow on Tuesday, but today - Friday - it is going to be 80 deg.)

Steamhead

TBrown said:

....... From the discussion, it appears the first and simplest thing to address is the bucket traps being used for EOM and drip traps.

The relatively high steam pressure (8 psig) was also something that we can easily address. This also was a flag to me, but thanks for confirming.

Right on both counts.

TBrown said:

I do not currently have a photo of the radiator traps, but the are inline traps installed below the convectors with no unions - that is what makes them so difficult to replace.

Most of these inline thermostatic traps have unions built-in. Post a pic if they're not completely obvious.

retiredguy

@TBrown wrote, My suspicion is the thermostatic traps are bad in several locations. An infrared thermometer indicates several thermostatic traps with the same high temperature on both sides of the trap - about 195 deg F.

So, I have to ask and correct me if I am wrong; @ Jamie Hall, wrote in response to my statement that the thermostatic trap passing condensate at 195 F is working correctly is that, "On one thing I'm afraid I differ slightly with @retiredguy -- if the temperature of the pipe on both sides of a trap is the same, it is very likely that it is passing steam. Now it could also be passing a lot of very hot condensate, but I'd be very suspicious of it". Now, my knowledge of thermostatic rad traps is that the alcohol/water mixture in the bellows of the trap forces the condensate to cool before opening not allowing steam to pass. You can have steam at 195 degrees if there is an 8" to 9 " vacuum at that point in the system. (This could make for a great discussion and provide for an education in the workings of steam traps).

There was also a question of inline rad traps. Both Barnes and Jones and Hoffman make them and they can be purchased at the SupplyHouse.com.

Jamie Hall

Basically quite right, @retiredguy . The theory is that the alcohol/water mixture in the bellows boils -- enough -- at around 200 or so that it expands the bellows and the trap shuts. So if the condensate touching the bellows is below that temperature the bellows should open and let it go, and if it is above it should close.

Should is the operative word. Depending on exactly what got into the bellows in the first place, and what the pressure difference across the trap is, that opening temperature can vary perhaps as much as 5 degrees either way. My theory -- and it's just that and I could well be wrong -- is that if the temperature on both sides of the trap is high and the same, something hot is getting through it. If it's hot condensate, there really shouldn't be enough of it to keep the downstream pipe the same temperature -- within 5 degrees, yes, but the same? But... I could be off base on that.

As the pressure difference goes up the bellows will have more and more difficulty keeping the trap shut; over two or three psi it may not be able to at all. Not damaged (yet...) but just not strong enough.