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# Venting Question

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Member Posts: 57
I've got 3 Hoffman 75's on the big one, 2 on the medium one, and 1 on the small one. Sounds like I'm OVER vented on the smallest main and throwing off my balance?

I'm pretty sure that one of the 6 valves that I'm using is shot, is there a reliable way to test?

• Member Posts: 57
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Venting Question

Is there a rule of thumb for venting mains? Something like "One Hoffman 75 for every 250 cubic inches of air in the main...One Gorton #2 for every 1000..." Etc.

I've got three mains, one is almost 6 times as big as the smallest!

I did a little math and the smallest has about 300 cubic inches of air in it, the second has 952 cubic inches, and the biggest has 2088 cubic inches.

Up until last night I had one Hoffman #75 on each one, now I've got 1, 2, and 3 75's on them respectively (thankfully I had them in the house, they're not cheap.)

I'm tempted to leave a 75 on the smallest main, and put one Gorton #2 and a Hoffman 75 on the second, and 3 #2's on the third. That should give fairly even venting, but is it enough?
• Member Posts: 6,688
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In order to answer that

I'd need to know the length and diameter of each of your steam mains. Not sure if you posted this info before, that's why I asked.

• Member Posts: 57
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Length and diameter

The smallest main:

62" (5.2 ft.) of 2" pipe
91" (7.6 ft.) of 1 1/4" pipe

The other two start as one pipe at the header:

191" (15.9 ft.) of 2" pipe

There's then a T, the middle sized one continues:

94" (7.8 ft.) of 2" pipe
291" (24.3 ft) of 1 1/4" pipe

The biggest one continues:

440" (36.7 ft.) of 2" pipe
331" (27.6 ft.) of 1 1/4" pipe

The three come back seprately to the Hartford loop, and the venting is independent. Should I give half of the shared piping venting to each of the two larger mains?

Hope this is what you were asking for.

Thanks!
• Member Posts: 6,688
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That's exactly what I'd do

using the Master Venting method pioneered by Frank Gerety.

That means each tee-off from that 15.9-foot main gets 0.4 cubic feet added to it.

I'd put a Gorton #2 on the longest one, a Hoffman #75 on the medium-length one and a Hoffman #4A on the real short one. If they should need fine-tuning, you'll have some extras available.

• Member Posts: 6,688
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The 4A

is roughly 1/6 the capacity of the 75. That's why I said to get one. You'd need to go way oversize on the other two to equal a 75 on the shortest one.