Is this a "thermal trap", or ??

Al Roethlisberger

I have an old overhead gravity system that was converted to a closed circulated system many years back.  After several posts to this forum over the last couple years most here seemed to agree that my system was currently piped into the "new" boiler backwards from the original supply/return as the boiler output was no longer going into the "express riser" that goes to my attic.



That being said, I had one other bit of mystery piping from the original that had me wondering what it is, and if that changes any opinions on which "direction" I should re-pipe the boiler.



See the attached photo.  It shows an odd "U" shape that goes all the way to the floor.  This piping is currently the return from the system to the boiler, although this piping is directly connected as a straight unimpeded run to the "express riser" to the attic.



I was wondering why the original "dead men" piped it this way, and what function it has.  Also, does this change anyone's opinion on whether this current return piping should actually be the supply piping?  Not knowing how the original boiler was piped(it was changed out long before we had the house), I just want to be sure to pipe it back the correct orientation.



Thanks,

Al

Paul Pollets

Gravity piping retrofits

There are several ways to repipe a gravity system with a pump. When I use a cast iron boiler, I use a 4 way valve on the supply to protect the boiler from thermal shock. The pump is installed on the supply outlet of the mixing valve. Several controls are available to power the 4 way valve. Some use a system bypass, if the water content of the system is 3 times greater than what the boiler content is.  On gravity piping, the water content usually greatly exceeds the water content of new boilers. The boiler must be piped so condensation does not occur. If the system return water does not reach 130 within 5-7 minutes of boiler firing, you need a bypass and/or a 4 way mixing valve, or both.  Piping a boiler backwards is not recommended.

Al Roethlisberger

Thanks, but wondering what the "U" is....

Hi Paul,



Yes, I already have a pri/sec system design using a 4-way motorized valve and Tekmar 362 planned for my upgrade.



What I'm curious about is what this "U" is and why the original installers put it on what we now assume was the original supply side of the piping as this connects directly to the express riser to the attic.   However after a previous DIY owner replaced the boiler circa 1991, he piped this section of pipe into the boiler return.  That is what I was referring to being piped "backwards".



I'm just wondering about this "U", what it does/did, and any other thoughts one may have on why it is installed on this particular section of pipe.



Thanks,

Al

Paul Pollets

U Tube

I've never seen this type of piping before. The thermal trap is too shallow to act as a check valve, so it remains a mystery. 

digger_2

pipe support

I believe the pipefitter added the "U" as a support for the pipe itself. It appears to be resting on the floor. It was an afterthought, see the coupling in the riser.

Unknown

a ' u' is much easier

A ' u' pipe is much easier than to pipe a ' R' pipe.....

Al Roethlisberger

Thanks, I too think it is likely a vertical support

I'm actually glad to hear that the consensus is that this is likely just a structural support  versus some sort of thermal flow check as the latter may have confused me further given some past discussions on the "piping history" of this system



The "U" does indeed rest on the floor as it appears, and I too had wondered that if this wasn't a thermal trap then must have been some sort of vertical support.



Thanks again,

Al

Jean-David Beyer

Looks like a trap to me.

I do not mean an intended one. I agree with the consensus that it is just a structural device. But it is a trap, like the one under my bathroom sink.



Should one of those elbows at the bottom be replaced by a T and a valve so that could be flushed out once in a while?

Al Roethlisberger

Might not be a bad idea....

...I'm going to try to avoid breaking into any old pipe as much as possible when I do the boiler rework, but this may be a prudent option to consider.



Thanks for the suggestion.



Al