Vapor System Venting

Davidho

I have a vapor system that doesn’t get above an ounce of pressure unless 20 degrees or colder.  3 ounces dead of winter.  I have one 76 vacuum vent at end of supply  and two 76 vacuum vent end of return pipe.  The last radiator on the second floor to get steam only gets hot at the top of it out to the middle of the radiator.  You can hear water falling inside of it.  Sounds like water dripping into gutter. Always thought could be air lock.  After reading lost art of steam I am thinking so even more.  I am not ready to get rid of the vacuum side of this awesome system.  I have two more new hoffman 76 vents for back up. On the radiator it has a plug right where a vent would be on a one pipe system; comparing drawings in the book.  Worth putting one of my vents there?  I also have two plugged connections in my main where radiators were removed.  Hurt to put a vent there? Book says end of the main wasn’t sure what would happen with one literally almost in the middle of it. I have enough space to add a nipple and make the vent higher up than the other vents, if that matters. It takes 10-15 minutes to get all of the air out when the boiler sits off for more than 1 hour.  When the temp is upper 30s or above the thermostat is off and we just turn it on when we feel cool.  We set a timer for 28 minutes and than shut it off.  I may have an ounce of pressure in that time. Leave well enough alone or would I actually improve the system?  

Jamie Hall

First check all your traps. That radiator that is a bit slow to heat may have a failing trap -- or there may be one elsewhere on the same dry return. Also check if there is a crossover trap at the end of that steam main and if there is, if it is working properly. They are often overlooked

Make sure the valve on that radiator is open.

Assuming you do have crossover traps, you really should only need venting on the dry returns where they join before they drop to the boiler. Others elsewhere aren't going to help much, if any.

Your stable pressures tell me that you have adequate venting as is.

Davidho

Thank you for the reply.  I do not have any cross over traps.  The only trap is trane number 2 direct return trap and trane traps on each radiator.  I will check them out.

EBEBRATT-Ed

@Davidho

Wont hurt to but a vent in the middle of the main but I doubt that is your issue. Make sure the problem rad is no worse than level (it should have a slight pitch toward the trap.

I agree with @Jamie Hall it could be a bad trap. Also check the supply riser if you have access and make sure it is pitched so it cannot collect water.


The other issue that is very common and a lot of people miss is if you have another radiator with a trap (especially in the vicinity of the problem rad) that is blowing through it can pressurize the return line to the problem rad and keep it from draining.

Davidho

I checked all my traps by touching them.  I had everything good and hot.  Every radiator you would not want to hold your hand on too from top to bottom.  I can grab the trap and it feels ice cold from the connector nut at radiator to pipe.  Except one.  The whole thing is hot as radiator.  Also seems to be one that had piping replaced.  There is about a 16 foot horizontal run back to the main return.  The raiser part all looks pitched correctly.  Of course this in the crawl space of the house and pipe runs above our a/c air handler.  I am going to have to crawl back there and see if I can see better on how the piping is pitched. The pipe here coming from the trap is warm. 

Jamie Hall

When the radiators are running at full power, the inlet to the trap should be at, or very close to, steam temperature. The outlet should be warm to hot, but at least 5 degrees cooler than the inlet.

Davidho

Every radiator but that one feels room temperature from my thumb and over to right. I guess I try running longer.  30 minutes and couple ounces pressure juat that one gets hot from where my thumb is and to the right.

 Update was real cool and hasn’t ran since morning; guess I didn’t have it good and hot like I thought. Turned it back on and everything like you described @Jamie Hall.  I have opened that trap on the troubled radiator a couple times when everything is cool, there is no water. Maybe I will try one of those infrared laser thermometers.  Or build that test station in the book and do it that way.  Thanks again for the help.

Jamie Hall

I think you have a trap element replacement project coming up. If you give Tunstall a shout with the make and model of the traps they can set you up.

Davidho

Thats what I am thinking.  Just replace every single one and be done.

EBEBRATT-Ed

@Davidho that's probably the best thing to do just rebuild all the traps. They can be a little difficult to troubleshoot.

Some advice if 1 trap blows through and passes steam it can ruin other traps. Wait till you don't need heat and do them all at once

Davidho

This morning I figured I would open the trap on noisy radiator while running.  The noise is coming from the inlet pipe to radiator. First opened little air pressure came out unscrewing the top and there was no pressure at all coming up through the return.  I was able to catch it on video when very little water running out of radiator into trap.  Posted link.  The riser is pitched correct coming off supply and than goes straight up to second floor to radiator.  This supply pipe is right at the end of the run before a 90 turn and a 10foot run to end of main.  I replaced the 10feet the 90 and the 2 feet going to the fitting that has the riser going to this radiator.  Wonder if junk in the riser piping or something?
https://m.youtube.com/shorts/fvlN8QKm8hk

delcrossv

Valve open?

clammy

Try blowing through the return piping . I ve run into a few where the return was clogged seems to usually be on the the return drop at the first 90 ,first clue was removing the trap and blowing in the return if there’s restriction then there must be some crud built up in the piping ,enough crude and the air won to vent and the rad will never get hot or take forever . If a trap is fail open and not passing steam into the dry return then the return is clogged .
Peace and good luck clammy

Silkey

My 1920s radiators with original Safety Vapor orifices, no traps per say, had rust, metal shavings, and crud just inside the lip on the radiator. Using a magnet and small wire hook I was able to get a significant amount of debris out of a few radiators........while converting to traps.

Insulate those pipes! At least all the hot supply to keep the steam heating the areas you want. I did the returns in the rubber type insulation.

1" fiberglass recommended (R6). There is a tax credit available and the savings will pay for itself within a few years. The existing white cardboard stuff may be hazardous and has an R2 rating.