What is the impact of faulty radiator vents?

bipbap

Hey All, this is my first post after being a longtime reader...

I was curious about what affect faulty radiator vents could have on my one-pipe steam system? If a vent is stuck open and air continually passes out through that radiator, does this mean the system will not achieve the proper pressure because there is essentially a leak in the system? Or will it just start spitting steam?
Similarly, what is the affect of radiator vents that are stuck closed?
Can one faulty vent stuck open or closed affect a system of 20 radiators?

I'm a newbie, be patient with me- thanks for the advice!

KC_Jones

The answer to your last question is yes.
If a vent is stuck open the worst that can happen is you are dumping steam which then leads to water loss. Water loss means extra makeup water, extra make up water means oxygen which corrodes the boiler shortening it's life.

If a vent is stuck completely closed a radiator won't heat much if at all. This can cause imbalance in the system, basically uneven heating.

Is there a specific problem you are seeing that you are asking this question?

Fred

If it is stuck open, you may not notice a problem until it is cold enough outside to cause that radiator to heat all the way across. When it does, you will see steam coming out of the vent.
If it is stuck closed, the radiator probably won't heat up because the air can't get out of the radiator to let the steam in. With 20 radiators on that system, I doubt that an imbalance would be immediately noticeable, except that room may be cold (stuck closed) or very humid (stuck open).

bipbap

Ok thanks, that's very helpful and makes sense.
But now if that vent is stuck open and steam comes out, would that prevent the system and therefore the boiler from ever reaching whatever pressure the vaporstat is set to shut of at?

Fred

It will cause you to use a lot of water and that's a bad thing. If your boiler is sized properly, (and it sounds like it might be)you should never reach the cut-out pressure on the Pressuretrol/vaporstat. That's a good thing. What is the cut out pressure on the Vaporstat set at?

bipbap

Good question- we just had the vaporstat installed and the guy may have been half-knucklehead because I think he did a good job installing but then he didn't seem too knowledgable about setting it.
Any advice for smart settings for the main and diff?
Thanks

Fred

I have mine set at 12 ounces (Main) and 8 ounces (Differential) which makes Cut-Out at 12 Ounces and Cut-In at 4 ounces.

bipbap

Ok thanks.
Is that just a good starting point for any one-pipe steam system?
Or are there factors which would suggest trying a higher/lower setting?

Fred

In reality, if your boiler is properly sized and you have good main venting AND the boiler is piped like it should be, you really won't reach the12 ounce Cut-out on a normal heating cycle. If you use Set-Backs, you might reach it during temp recovery/longer heating cycle.
Depending on the Vaporstat you have, some are 0 to 16 ounce others are 0 to 4pounds, you can adjust the Main up to 1.5PSI but you really never want to go over that pressure. On a subtractive Vaporstat, all the Differential does is close the micro switch at the Cut-out pressure minus the differential, so 12 Ounces minus 8 ounce = 4 ounces. In this example, should your system pressure reach 12 ounces and cut the burner off, when the pressure drops to 4 ounces, the micro switch will close and allow the burner to fire again.
Even though my Vaporstat is set at 12/8, my typical system pressure stays at about 2 ounces. On very, very cold days, I might have one or two cycles where it will cut out at 12 ounces but my boiler is over-sized. The goal is to let your boiler run at a reasonable pressure (max 1.5PSI) but not to try to set the Vaporstat or pressuretrol so low that it shuts the boiler down because you have it set at an unreasonably low pressure setting.

mikeg2015

If you vent "aggressively" the pressure required is based on pressure drop in the pipe if your boiler is sized for the connected load. So if you have a nice big header, you might never see more than 1-2oz. Of course at that pressure, vents don't move much air.

But as always, if you need more than a few ounces of pressure, you should start by putting in biggest main vent possible to match the size of the tapping (1/2" or 3/4"),then go from there.

This is after running for at least 15 minutes. Radiators were about 2/3 heated. From a cold start, the first 5 minutes of making steam its between 0.5oz and vacuum as it heats the big 3" header.

mikeg2015

... I also don't have an equalizer pipe, but at this pressure it's not really an issue.

Fred

@mikeg2015 said: But as always, if you need more than a few ounces of pressure, you should start by putting in biggest main vent possible to match the size of the tapping (1/2" or 3/4"),then go from there.
Mike, Vents are sized based on the amount of air that needs to be removed from the main(s). That takes into consideration the length and diameter of that main. Also, vents are rated for their capacity to exhaust air based typically on 1 ounce, 2 ounces and 3 ounces of pressure, for most residential systems, higher ratings for some commercial applications.

bipbap

Sorry for the silence-- so ours was set at MAIN .75psi and DIFF of OZS IN2.
How does that sound?

bipbap

Sorry- I meant a DIFF of 7 OZS IN2

Fred

That sounds fine. .75 = 12 ounces, with a 7 ounce differential makes a Cut-in of 5 ounces. That will work well for you.

bipbap

Ok thanks for all the help- I'll keep it set like that and see how it goes. Thank you!