Hoffman 75 vs. 74

Michael Stoic

As far as I can tell from the ITT specs, the difference between Hoffman 74 and 75 is drop away pressure (Max 3 PSI for 75 and Max 35 PSI for 74).

Any harm in using 74 in place of an existing 75 ? [9 unit 3 story residential building]

Steamhead

The 74

> As far as I can tell from the ITT specs, the

> difference between Hoffman 74 and 75 is drop away

> pressure (Max 3 PSI for 75 and Max 35 PSI for

> 74).

>

> Any harm in using 74 in place of an

> existing 75 ? [9 unit 3 story residential

> building]





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Steamhead

The 74

has a very small venting port, and really should not be used on low-pressure systems. It will not vent fast enough.

In a 9-unit 3-story apartment building, it's likely that even the 75 is too small. Measure the length and diameter of your steam mains and we'll tell you what you need.

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Michael Stoic

Thank you for answering my question! I'll take you up on the offer to size the vents in a few days.

MS

thfurnitureguy_4

main vents and a cold radaitor

I have a commercial bldg with a single pipe system. The steam supply pipes run along the celing of the first floor with the boiler and main vents in the basement. first question: I have 2 mains runing down both sides of the bldg. About 250' from the boiler. The steam to the first floor is piped down from the celing to the floor,across a few joists (6') and up through the radiator. This radiator will heat 3 or four of its 15 sections before the cycle is over. The radiator vent is opened fully and the steam heat is reaching the main vent in the basement (The steam pipe is hot at the main vent) I assume that the vent is not large enough to vent the size of this radiator. With the vent removed it will just warm the last section near the end of the cycle. It seams like a 1/4" hole is a very large vent hole. The radiator across the bldg ( the same distance from the boiler, and on the same floor, heats up 3 or 4 min. before the large radiator I spoke of before. It is piped derectly off the basement main at a T . Its supply pipe is about 15" long.
Second question: Is it a problem to have the mains join into a common return at the end of the run there are 2 main vents (Hoffman #75) before the Y? Thanks for any help

Steamhead

Venting

Try a Gorton #D vent in that big radiator. But first, you need to vent the mains properly. Are they 250 feet long like your post says? What pipe size are they?

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thfurnitureguy

Pipe diameter

Thanks for the info on the gorton "D" valve . My pipe masures 4" OD and with the ups and down to the end where the main valves are its closer to 300 feet of 4" pipe

Steamhead

That's a lot of 3-1/2\" pipe (4\" O.D.)

but is it a single run of 300 feet from start to finish, or a pair of 150-foot runs from start to finish, or two 300-foot runs from start to finish?

A 300-foot run of 3-1/2" pipe requires a lot of venting to work right. Install five Gorton #2 vents at the end of this main. Then watch how well it works.

For a 150-foot run of 3-1/2-inch, two #2 vents should be fine.

www.gorton-valves.com

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