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Main vents

Brad White
Brad White Member Posts: 2,398
reducing the pressure?

I would expect you to hear venting well before you build up to 1.5 lbs.

Well, let me re-phrase that.

The venting rate should be high enough and unrestricted enough that you should not hear it much at all.

In other words, can you "feel" venting rather than hear it? Silent venting seems so much more valuable. As you said, the mains are warm which means steam is getting in, thus air must be getting out...

I suspect that they are venting, just not bragging about it.

I would crank down the pressure to make your steam bigger and see what happens.

When firing stops and it goes into a down cycle, do you also hear them sucking back in (vacuum breaker mode)? That can be noisier than the out-venting too. Might that be what you are hearing?
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-Ernie White, my Dad


  • Glen_7
    Glen_7 Member Posts: 82
    Venting mains

    After a new steam boiler install replacing my old monster, I am re-tuning the system. My 3 mains (2 1/2" mostly) run from 70 to 95 feet. At each end, there are 3 Gorton #2's. Once I build my pressure to 1.5 lbs, I can hear the mains start to vent, although they are quite warm to the touch well before that. From what I have read here and elsewhere, steam at that low pressure should vent those mains in about a minute. Mine take about 15 minutes to vent and close. I had the same condition with the last boiler. The vents don't sound like they are venting at full capacity so I'm wondering why so long? All pipes/joints, etc newly insulated w/1" split fiberglass.

  • JK_3
    JK_3 Member Posts: 240
    boiler size

    have you done heat loss calcs to make sure that your boiler is the right size?

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  • Glen_7
    Glen_7 Member Posts: 82


    Yes, the EDR was 1340 or so and the new boiler is rated at 632 input and 1601 sq/ft of steam. My old boiler was way oversized and the same thing happened. With this one, pressure build takes longer, but when the needle starts to budge, you can hear the mains pushing air. They take some time to clear and as I mentioned, I have 3 triple Gorton #2's on each. As Brad mentioned, since the end of the mains get warm in about 10 minutes, you would think steam was already there. If so, why is the air still pushing out a half hour later and then taking so long to vent.

    I'm going to have Matt Sweeny take a look but thought I would post this first to save him some time.

  • Having Matt look at it

    is the best thing you could do. Let us know how it works out.

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