Working vents don't close

alexru1

Homeowner with a one pipe steam system hoping someone can have suggestions. I have a vaporstat and running around 1/2PSI and have working main vents in the basement. My house has convectors on the 1st floor and cast iron radiators on the second floor. All radiators are pitched back to the pipe and heat up fast. All of my vents close as soon as steam reaches them, but one of the radiators (my largest one) has a problem closing the vent for some reason. I used 2 new Hoffmans and tried a Gorton from another working radiator. I also tried Maid-o-mist with various flow rates and currently using Varivalve. With the Gorton, the valve just does not close at all, it lets the steam out and makes steam noise when it reaches it. With the hoffman, it makes noise for a minute and finally closes. Varivalves seem to work best but still spit out some water for a few seconds before closing. I have this radiator pitched down to the pipe and thought that the pitch is too high for a float type vent thinking that the float needs to be more level, but removing the pitch and bringing the radiator to the floor did not fix anything. The rest of the system work great with vents closing on time with no noise, so I'm at a loss. Any ideas?

nicholas bonham-carter

Is this while recovering from a setback?
Have you got generous main venting? If not, then putting the burden of the air removal on the rad vents can sometimes blow debris up into those, and cause the vent not to close. Wash out your Hoffman vent, and try a constant temperature.—NBC

STEAM DOCTOR

My gut feeling would be that the vents are the symptom and not the problem. Might be something causing excess water in the radiator or in the piping leading to the radiator.

alexru1

Thanks. I cut off at .5 and cut back just above 0. I don't have a separate pressure gauge yet and the 30psi is useless so can't say for sure, but based on playing with the vaporstat it's as low as possible. The mains were here when I bought the house and seem to work, but they are not huge. I think it's ventrite. I was thinking of changing them but everything seems to heat fast and at the same time

alexru1

Forgot to mention - Vents are not clogged. I'm using new vents that tested on other radiators

Fred

How about a picture of that radiator and the vent. I suspect that the fact it is the "largest" radiator on your system is a clue. It may well be that that last section of the radiator just doesn't get hot enough, during a normal heating cycle, to actually cause the vent to close.

alexru1

I'll take a picture later on but it does get hot, but I was thinking the same thing about not hot enough and if bigger main vent would help the steam to be hotter. Are some vents set up to close at lower temp?

Fred

alexru1 said:

I'll take a picture later on but it does get hot, but I was thinking the same thing about not hot enough and if bigger main vent would help the steam to be hotter. Are some vents set up to close at lower temp?

Have you felt both the top and bottom of the radiator. If it is vented too fast, either the top or bottom may, in fact be cool because the steam has raced across the radiator but maybe, combined with air still trying to escape, the vent simply doesn't get hot enough to close. It may be that you are trying to make all the radiators hot all the way across, rather than make the room comfortable. A radiator doesn't need to be hot all the way across to heat a space and given this is the largest radiator, it likely doesn't need to fully heat. Is this radiator in the largest space and with the greatest heat loss? If so, how much larger?

alexru1

It gets really hot on top and middle by the time it gets to the vent. The bottom is cooler but warm similar to my other working radiators. I do feel the radiator is oversized and I don't want it to heat all across. I installed a danfoss thermostatic valve to help with that, so if TRV gets to close it before the steam gets to the valave, I have no problem, but if TRV remains open, the problem occurs just like without the TRV (I feel like it is even worse with the TRV)

alexru1

See picture of the radiator. Thank you for your suggestions

Fred

Does it behave the same way without the TRV on it? Don't some of those TRV's require a vacuum breaker on them. Is it possible that a vacuum is pulling the vent open?

Mike Cascio

What size is the supply vale on the radiator? A picture of the valve would help. If its too small there may be condensate in the radiator not draining.

alexru1

These trv have a built in vacuum breaker as far as I know. I switched trv with my smaller radiator that is working properly and had the same issue with this radiator and the TRV worked well on the smaller radiator

JUGHNE

As Mike said concerning the size of the steam valve and also the size of the pipe riser thru the floor and the horizontal run out from the main to that riser, and how long is the run out? And it needs good pitch for the condensate to flow back against the steam flow.

Steam will flow thru any pipe but it has to cope with condensate returning on the bottom of the pipe. Sometimes not room for both. Also some steam valves just do not have enough passageway for steam in and a lot of condensate flowing out.

acwagner

@alexru1 do all your radiator vents close on a normal call for heat? Also, do you know if your boiler is grossly oversized relative to your radiator capacity?

The others have good things to check. Beyond their recommendations, my theory is that since this is the biggest radiator and on the second floor, it's probably the last vent to close. If the boiler is way oversized, it might be quickly building up pressure in that time interval which is impeding the vent from closing right and/or causing the hissing. I have vents on my own system that don't close at semi-low pressure (0.5 psi) like they should--and that would possibly explain the variable results you got with different vents you put on that radiator.

Perhaps get a 0-3psig gauge and see what pressure you're actually running at when that vent on the big radiator is about to close.

Jackmartin

Put in two vents one slightly higher than the othetr one looks in Dans book really big rads need more venting. Try raising your boiler oressure to one pounf you are running it too low. Remember single pipe steam runs at .5 on 2 psig off. The deadmen ran single pipe at this pressure because it worked. You never want a single pipe system to hit o psig you are using gas to heat cold water. All the best Jack

Fred

@Jackmartin he's got one vent that won't close. Why would he want two of them? Radiator Vents don't close on pressure. They close on temp so increasing the pressure won't fix anything. If he is getting heat to all the radiators, he has plenty of pressure and the deadmen didn't run steam at .5 on and 2 PSI off. They knew low pressure was key to good steam flow. The .5 PSI means that the boiler will fire at anything at or below .5 PSI and that it will run best at anything up to 2 PSI. Most of us don't run anywhere near that pressure and the Pressuretrol is actually used as designed, as a safety device, not an operating device. It only becomes an operating device when someone over sizes their boiler, usually because they didn't do their homework before deciding on boiler size.

Mike Cascio

You can try venting the riser and keep the venting of the rad slower. I recently put a vent in the unused tapping of the valve side of the rad then a slower vent in the normal location. This will get the steam to the trouble rad quickly and then vent the rad slowly and completely.

alexru1

The pipe is 2inches. How do you put a second valve? I'm afraid it will cause two of them to make noise. This is the last radiator on the main. So I can increase main venting but didn't think it's necessary because all radiators start heating up at the same time.

alexru1

Is this a plug? I don't see how to get this out. Would this really help?

Mike Cascio

Yes, thats a plug. It would have to be drilled and tapped to 1/8 npt. Then I would put a faster vent there and a slower one on the other end of the rad. That valve looks like 1 inch, but its hard to tell.

Fred

You don't need more radiator venting. You are getting steam into that radiator. It's just that the vent you have on there isn't closing. If you add another vent in that tapping on the same side as the supply valve, it will do nothing as it will close as soon as steam gets to that radiator. If your issue is that the vent isn't closing, that's one issue. If the vent is actually hissing and it's the last radiator on that main, that's a different issue and may be an indication that you may need more main venting or that the main vent is closing before all the air is evacuated. Which is it?

alexru1

The vent is silent until the steam gets to it. Once the steam gets to it it starts to make boiling noise and and let steam out slightly (it seems like its halfway closed). Depending on the brand of the vent it will close after some time or it will remain open with Gorton valves. When I tried to use TRV from another radiator last night as a test, I had the same issue with this large radiator but not others but I noticed some water in the TRV when I was changing these back. Could the water stop the vent from fully closing? Why are the other radiators working with the same setup?

alexru1

My mains close after they get hot. The don't seem to be anything super fast but as I said before everything heats up evenly so I'm not sure if I need an upgrade. Mains are VentRite35

Mike Cascio

Try a slower vent.

acwagner

Check the vent/TRV assembly and see if it is pitched to drain toward the radiator. The vent tapping could be slightly off such that even though radiator itself has pitch the vent could be back pitched. Doesn't look that way in the photo, but worth checking.

Fred

If you have Vent-rite #35's on the main, you need bigger main vents. A Ventrite #35 will only vent .110 CFM of air at 1 ounce of pressure and .25CFM at 3 ounces of pressure. Radiator vents will vent at that rate and you are expecting them to vent the entire main/header. Your radiators may all be heating evenly but those radiator vents are handling the majority of the air in the system. Stop trying to fix a radiator vent and put decent sized vents on the mains. Your problem will go away. What is happening is steam will take the path of least resistance. It is pushing air as much as it can out of that small main vent and then, by the time it get to that last radiator run out, that larger radiator becomes the path of least resistance and it push the balance of the air in the main and the radiator out through that radiator vent. By that time, I suspect the thermostat has been satisfied, or very close to being satisfied and the system shuts down and then what happens? The steam in the system collapses and air is sucked back into the system. Where will that happen? At the radiator vent that didn't get a chance to close.

Mike Cascio

That ventrite 35 has to go. As Fred said its too slow. Whats the distance from the boiler header to that vent and what size is the main? That will help determine what vent should be there.

alexru1

19ft. Pipe is 2 and3/4inches

Jackmartin

I am back from dinner with my family so I can finish this comment. If you are running a real one pipe system -- what allows the water to return to the boiler, the A dimension and the left over steam pressure left in the piping. You are going to 0 psig where are you getting the required A dimension at 0 psig -- you are not. The rads are not being emptied of all the condensate because you are not running a steam system you are running a scorched air system -- the furnance comes on the fan runs and everything shuts down until the next cycle. Steam is a living thing, in the mechanical sense ,it should never be shut down -to- 0 psig until summer. Run the system the way it was designed, heating season rolls around the boiler is always "alive" ,until the heating system is over.The deadmen were smart ,they understood passive physics ,and one pipe steam is a study in using the rules of physics to achieve what you need to happen without the aid of pumps or any other mechanical device. Read The Lost Art of Steam Heating it will answer all your questions. All the best from Canada Jack

Fred

@Jackmartin, What allows water to return is gravity. That's why all mains, run-outs and radiators need some pitch. Also, the boiler is always at 0 PSI between cycles. The deadmen knew the only pressure needed was just enough to move the steam to the furthest point in the system, pipe diameter, length and number of turns drive some pressure loss but that loss is fractions of an ounce by diameter, length and number of turns. There are charts that provide that information. High pressure goes to lower pressures. That's relative. One ounce of pressure is higher than atmospheric. The old coal systems that the Deadmen installed had much less pressure than the average gas or oil fired modern boiler, even properly sized.

nicholas bonham-carter

Let’s not forget that gas at a very low pressure can travel quite a distance inside a building, so you don’t need much pressure.—NBC