False water line for pumped return system

Mike_Sheppard

I am looking for some guidance for properly designing and installing a false water line for a pumped return system, as described on page 55 of The Lost Art Revisited.

Has anyone here done it before?

I have a customer who had a new boiler and feedwater pump installed. They also converted from gravity return to pumped return. The water line of the feedwater tank is about a foot off the floor, well below where it used to be.

The saving grace is that they are running only 10 ounces of steam pressure and the condensate return drops below the level of the tank just enough to create a water seal to stop the steam from escaping into the tank.

They now have returns which used to tie together below the water line tie together above the water line. The building heats alright but they get a lot of banging in the formerly wet returns.

As @steamhead suggested in a different post, a false waterline would do the trick. But it is something I’ve never done and I want to make sure I am doing it correctly.

As TLAOSHR describes, you can use a 10 inch piece of pipe to receive the condensate return, supply steam to it as well to equalize the system (like a gravity system would be), and use one or two bucket traps to drain back to the feedwater tank.

This is a five story building, four units on each level, 20 total. Two 3 inch mains, and a 2 inch return at the tank. One pipe steam.

Will a 10 inch “tank” work here?

Is there a way to accurately size the traps without having to count total EDR? They have a 2 inch wet return which is good for a max of 4,000 EDR, would that be enough to size the two traps?

Should there be a drain at the bottom?

If using dip tubes inside for the traps should the top or bottom of the tank be flanged to allow repair of the dip tubes?

Would a 1-1/2 inch steam line be enough to equalize this?

Any advice would be much appreciated.

JohnNY

I’ve done a few false water lines. On some smaller residential systems, I simply created an inverted U on the return just before the boiler to drown all the parts of the system that were meant to be filled with water. It works well and cures a lot of problems. Often, I see evidence of contractors having tried everything under the sun to solve water line problems, adding pumps, traps, etc, when only a few short lengths of pipe and fittings will do.
On something closer to what you’re describing, in a 6-story office building in Midtown Manhattan, I used a ~60” long old expansion tank taken from the rafters of an old house to a welder who fitted it with 2” piping connections, trap outlet tappings, and a water column gauge. The tank is more like 14” around and that’s why I used it. The extra width handles more water and things just happen in a more slowly and controlled way in the wider space.
This particular job was a real success. It quieted the banging pipes down instantly, prevented steam pressure from getting into the returns, balanced distribution for the first time in years, and initiated a great dialogue between Dan Holohan and I who went through the whole process with as much curiosity and anticipation about what the end result would be as I had.
We did size the traps based on EDR of the system but I’d have to look in my notes to see what that value was and we used a 1” trap at one height and a secondary 1” trap at a higher connection in the vertical tank as a backup. The second trap never sees condensate but you’ll want to install one anyway. We had a 6” supply line with a 2” return. The tank, or pipe in your case, needs a drain. Debris collects in there and you’ll need a way to flush it out. This was a municipal steam project and we had to reduce our steam pressure from the incoming 160 PSI to 1 PSI, but most of that was already in place yet running at 5 PSI. Simple adjustments took care of that.
I’m away from my desk but I’ll try to find some pictures to post. Let me know if you need any help.

Mike_Sheppard

@JohnNY thank you!

I agree, the larger tank would be better, I was thinking that as well.

Did you use a steam line to the tank as well to equalize the system?

I would love to see some pictures if you have them. It was great meeting you and others in NY at the last get together. I’ve learned a lot from your posts over the years!

JohnNY

Hi Mike,
That's nice of you to say. Thank you very much.
Yes we did use a steam supply pipe on top to equalize the pressure. It's a difficult thing to photograph but here it is. The client is a very worthwhile non-profit and we did the job for no fee but it's not bad at all and we're happy with how it functions.

Mike_Sheppard

@JohnNY thank you for the pictures. This helps a lot. Great idea using the tank.

Is that a vacuum breaker up at the top? (The check valve)

Since that tank is a pressure vessel again, did it need to be inspected and approved afterwards since it was modified?

What is the purpose of the air vents after the traps? I’m assuming the line has a water seal somewhere before the feedwater tank which would require the air vents there?

As always, great idea and great work. Thank you

JohnNY

Yes. We found out we needed a vacuum breaker one day and so we made our own with the check valve. No inspections on the tank. I'm not sure who would even govern such a thing.
The air vents are after the traps because we send the condensate through a shell-and-tube heat exchanger (donated by Taco) which the hot water recirculation line runs through to pre-heat our DHW for free, and to temper the hot discharge to a Code compliant temperature before dumping it into the city sewer system.

Mike_Sheppard

@JohnNY ahh I see. I forgot you mentioned it was district steam. We don’t have any of that here in DC.

I know we have to have pressure vessels inspected down here, I’m not sure if something like this would count but I will look into it.

Thank you a ton for the pictures and info. One of the guys in this co-op building is from NY and he knows a decent amount about steam systems. I’m sure he can count th EDR for me.

This will be a summer project. I will start writing up a report for them tonight.

Thanks again!