When to use an F&T trap at end of main ?

delcrossv · December 15

As opposed to a thermostatic (radiator) trap? Seen both, is it dependent on condensate volume, or something else?

Designer's choice? Some small systems have F&T, some larger systems make do with a rad trap (???)

EBEBRATT-Ed · December 15

F & T is better if you have a lot of air to pass through it. In some cases you can use either one.

The weigh to properly size an end of the main drip is something most people do not know how to do and they usually install traps far larger than needed.

You measure the length of the main and accounting for any reductions in pipe size you add up the WEIGHT of all the pipe, valves and fittings. Then you take the specific weigh of the steel pipe and knowing the weight and specific heat you calculate how much condensate will be formed bringing the steel pipe from say 50 degrees to the steam temp (212) or whatever, Then when you get the condensate volume from that you apply a 1.5 safety factor to that.

In most cases a 3/4 F&T is more than large enough.

Alot of peopel put on a steam trap as large as the drip leg which makes it 4x the size it needs to be and wire drawing will shorten the trap life.

Jamie Hall · December 15

Um… well, it depends a little on the overall setup, in my view. If you have an arrangement with a steam main and a parallel dry return and, if you are really lucky, a parallel wet return, then the simplest solution is a crossover trap for the air to go into the parallel dry return, and drips from both the steam main and the dry return to the wet return to handle the condensate.

Crossover traps can be normal size radiator traps, but if you have more air to handle you can go to a larger size but still quite normal thermostatic radiator trap. They pass a remarkable amount of air.

In my view at least you really have to be dealing with a lot of condensate to justify the order of magnitude higher price — never mind the maintenance — of an F&T.

If you don't have a handy wet return, but you do have the headroom, a simple water seal will handle as much condensate as any residential or small commercial system will create, with the only stipulation being that you have to keep the pressure in line (which you should anyway).

EBEBRATT-Ed · December 16

Loop seals are the best and underutilized.

I had a funny system I serviced in an old Town Hall that was built during the Civil War. Of course, the heating system was not quite that old but over the years some of what was a vapor system had portions of the building that were one pipe, and some was 2 pipe.

They had complained that they had water squirting out of the vents on the first floor of the one pipe section. About 5 good sized one pipe rads were hooked into a main and at the end of the main was a 3/4" F & T dripping the main. I had looked at this and everything looked fine to me. I checked pipe pitch etc. Then I realized that this one pipe main was carrying not just the end of the main drip but all the condensate from the 5 one pipe radiators, so the trap was very much undersized.

Lucky for me the 3/4 trap discharged into a dry return that was 12" below the main. I was originally going to leave the job and go searching for a 1 1/2" trap which was going to be an hour and a half trip.

Then I thought of a loop seal.

I was able to pick up some 1 1/4" pipe and fittings locally….plus what I scrounged off my truck. I had to thread it all by hand but I had the height to put in a 60" loop seal.

Worked like a charm and never needs any maintenance unless the loop seal collects sludge.

The maintenance guy was so happy I fixed it. They also needed a new boiler which they had to go out to bid for but we didn't get that job.

Figures. No good deed goes unpunished.

delcrossv · December 16

So, as I understand it, a water seal needs a vent at the end of the main to release air, yes?

Jamie Hall · December 16

https://forum.heatinghelp.com/discussion/comment/1827090#Comment_1827090

Either a vent or a crossover trap to a dry return. Take your pick.

EBEBRATT-Ed · December 16

Yes have to have a place for the air to get out before you drop to a wet return. As the return pipe fills with water you can sometimes let the air back up and go out the radiator air vents if you have them but if you have traps on the rads that will not work.

When to use an F&T trap at end of main ?

Comments

Categories