How many Gorton #2 per main?

A one-pipe steam main is full of air when the boiler fires. Main vents at the ends of the mains have to dump that air before steam can fill the pipe. How many Gorton #2 (or #1) eliminators you need depends on three things you can measure or choose:

1. Main pipe size and length — nominal ID and run length of each section that vents through the tapping.
2. Target minutes — how long you will give the main to clear (often a few minutes; confirm against how the building actually behaves).
3. Working boiler pressure — capacities are published at 1 / 2 / 3 oz columns; pick the column that matches how the boiler is set (ounces, not PSI).

Walk each steam main from the boiler header out to the venting point. Note nominal pipe size and length for every section. The calculator converts Schedule 40 internal diameter into cubic feet per linear foot (ASME B36.10M), then multiplies by length.

Add the sections that share the same end-of-main tapping. That sum is the air volume the vents on that tapping must clear.

Required venting rate is straightforward arithmetic used in the Gill & Pajek balancing method:

Example shape only — plug your own lengths into the calculator: a long 2" main holds more air than a short 1-1/4" run, so the same target time demands more vent capacity.

Divide the required CFM by the published capacity of a Gorton #2 at your working ounce column (1.1 / 1.75 / 2.2 CFM at 1 / 2 / 3 oz). That quotient (rounded up) is how many #2 eliminators to start with. The same math with #1 capacity (0.33 / 0.54 / 0.70 CFM) tells you the alternate count — Gorton states a #2 is equal in venting capacity to four #1 eliminators, and the instrumented Gill & Pajek chart is what the calculator uses for absolute CFM.

Do not copy CFM figures from memory into a takeoff. Open the main vent sizer, enter pipe and time, and read the count from the cited table. Also watch the open-pipe ceiling on the tapping: no stack of vents can pass more air than the tapping itself will allow.

Gorton also catalogs a larger “Big Mouth” main vent; it post-dates the 2005 test program and has no published CFM in that chart, so the calculator shows it as a gap rather than a guessed number. Use it only with manufacturer guidance and field timing — not as a drop-in substitute for a #2 count from the measured table.

The published method treats the calculated count as a starting point. Pull a vent, fire the boiler, and time steam to the open pipe; reinstall vents until you land near the target. Cold returns, pitched mains, and dirty valves all change the clock.