Commercial steam building main venting

tuli

Hi!



I'm a little new here (and new to the steam heating field as well) so i'll try to put as much info in as little words. I've been reading here all night about proper venting for main runs, and for the most part i'm seeing discussions which look like they are for residential applications or small commercial.

I'm having an issue with a 6 story building that's not balanced properly. I went down to to look, and for some reason,  previous serviceman had installed a Hoffman 75 on the mains all along the way right near each riser going up. Now from what i understand this is not correct, but is it doing any harm? Since there is the same Hoffman 75 at the end of the main as well?



Thanks in advance for all the help.

nicholas bonham-carter

6 stories venting problems

if he had put the Hoffman 75 on the top of the riser, it would have done more good. can you tell us what vents are on the dry returns just before they drop down near the boiler? Hoffman 75's are good quality, but quite slow, and therefore Gorton 2's are better, but for your system you may need several dozen to handle the air removal arranged on antlers on each dry return. an option would be the use of a trap to handle the air. the Hoffmans could then be put on the top of each riser.

A low pressure gauge [0-3 psi] would enable you to see when you have enough main venting. the goal is to have such low resistance [back-pressure] that you are no longer paying for extra fuel [10%?] to push the air out. in your situation, there will be a short payback.

Are the radiators all heating at the same time?--nbc

JohnNY

Answer

No, the Hoffman 75s placed midway along the mains are not doing any harm. There are better places to install vents, but they can be installed in addition to what you've got in place now. Hoffman 75s basically vent the same as Gorton model #1 vents, but the Gorton model #2 vents 400% more air than the #1. Consider having the #2s installed in strategic places in the piping.



My company is repiping a steam system in a 6-story, block-to-block building in Manhattan as we speak and venting is a big concern.

tuli

Got a better look

I went back to the building today to get a better look. There are a total of 4 mains coming from the boiler. Each main feeds approx 12-16 risers (each being between 1-1/4"-2") in a span of approx 150 ft. Along these mains, approx every 30-40 ft, there is a dry return with 1 Hoffman 75 on the return. I have enclosed a picture of those dry returns and the air valve.

What i am seeing is, all the air valves are shooting out a significant amount of steam. Am i correctly assuming that they are all defective?

nicholas bonham-carter

Watery vents

Either they are defective, or the pressuretrol (clogged pigtail?) is (more likely). They can only stand so much pressure. An accurate low-pressure gauge (0-3 psi) would show you the true pressure, which should be below 1.5 psi, or could be ounces for more economy.--NBC

tuli

thanks

Thanks for the tip. I will definitely look into the pressure. But don't these big boilers have 3 or 4 pressuretrolls? I'm sure at least one would work?

nicholas bonham-carter

Multiple pressuretrols

Yes: safety(reset), high fire, low fire, and medium fire.

If they are on a common header, they could all be unable to feel the steam pressure.--NBC

Dave in QCA

Try Cleaning the Vents First

From my experience, the Hoffman 75 vent usually last a VERY long time. However, they seem prone to building up a little scale that stops them from properly seating. Some recommend soaking in vinegar, but I have found using Limeaway or CLR to be a much fast and effective way to clean them. You have to remove them, then squirt some of the product into the vent. Close it with your thumb and shake it. Let it set for a minute or two, empty, rinse, and repeat. Second time, let set for 5 minutes, then thoroughly rinse and re-install.

tuli

correctly vented?

Still didnt get a chance to get back there to get a gauge on it to test the pressure.

But in the meantime, i have a question like this. This is a 6 store building with numerous lines, and they are having significant issues with balancing as some apts are not getting adequate heat. Is the fact that they have air valves along the way, meaning on each dry return pipe along the mains, affecting the rest of the main? meaning do the last lines of these mains get less heat because of the air valves on the returns along the way?

nicholas bonham-carter

Imbalance of heat

The ends of the returns are the best place for the vents, with additional venting on tall risers. The risers could be vented by the top radiators, having fast Gorton d's, with the other rads more slowly vented by Hoffman 40's.

The air will escape using the path of least resistance, so arrange the placement of those points of least resistance (the main vents) at the ends of the returns and the risers. When the pipes are full of steam, before the radiators, then the radiators all begin to get steam simultaneously.--NBC

tuli

suggestion

In you opinion, would I be wiser to remove all air vents along the way and just add on addl vents at the end? Or leave the existing ones in place andadd on at the end of the run?

Dave in QCA

might be ok

In pondering your main venting set up, it is the usual method for all main vents to be installed at the end of the main. However, if applying math to your situation, it appears that it might actually work OK, but I would guess that you would need more vents to achieve balance. My reasoning, if I am not in error, is that as the steam travels down the main, the first vent would close, leaving only the remaining vents open, but at that same time, there is less remaining main to be vented, and so on as the steam travels down the main.



The Hoffman 75 is a very well made and reliable vent. Common problem of not shutting tightly on steam can usually be corrected with cleaning. The Hoffman stays 100% open until it is steam conditions, about 190F, at which point it snaps closed. The Gorton #2 when cold will vent a little more than twice as fast as the Hoffman 75, but a problem exists that they do not fully reopen until around 134F. After a heating cycle, they will remain closed until somewhere around 160F. So, in a system that has fully insulated mains and cycles 1 times per hour, the temperature of the main may stay warm enough that they Gorton does not fully reopen, in fact, in my system, the Gortons often did not reopen at all. You could get a good thermometer and insert it under the insulation to determine what temperature your mains are, say 55 minutes after the boiler shuts off.



There are two essential parts that should allow you to get even distribution of steam. They are fast venting of the mains and slow venting of the radiators. You have not indicated what kind of radiator vents you are using, but if they are too fast, they can cause a complete imbalance of the system.