Main vents

After re-reading

 "Venting Steam Systems Using A Capacity Chart" Page 1 and 2, it appears that the amount of air in the steam main has little to do with the amount of venting that is nescesary to vent the main to the max.  The amount of main vents is calculated based upon the size of tapping they are mounted on, and the speed your boiler can send the steam to your 3/4" opening.  You have a 3/4" tapping, build yourself a 3/4' antler, install the vents you have all-ready purchased, and, as your budjet allows, keep adding Gorton 2's until you can get steam to the vents, in nearly the same amount of time, as an open 3/4" hole.

Correct me if I am mistaken, but this is how I read the directions.  I have two 75 foot mains with 2-G2's, 1-Hoffman 75, and 1-G1 on each side.  From the time my boiler opens the damper it takes 4 minutes for steam to hit the vents.  On a cold start it takes about 7 or 8 minutes.



The reason for the 1, 2, and 3 oz scales is that is the pressure each vent was tested at.  

Attempt to explain

When your boiler is first producing steam, and your main vents are open and venting, you don't have your normal operating pressure yet, no matter where your high limit is set at.



The three columns indicate flow rates of the tested devices at 3 different pressures.  As the steam starts to come rolling down the main, and the air is escaping, there will be a very slight pressure above 0 psi.  It is usually near 1 oz, from my limited experience.  So, if you were to assume that the steam as it starts to travel is going to produce 1 oz of pressure in your system, a Gorton #2 would vent at the rate of 1.1 cfm and a Gorton #1 would vent at 0.333 cfm. 



If the pressure was actually at 2 oz at the point that steam begins to travel out from the boiler, then you would read the flow rates under the 2oz column.



Think about it this way...  If you put a Gorton #1 in your mouth an blew real softly, say just hard enough to produce 1 oz of pressure, the flow rate would be smaller than if your blew REAL hard, say hard enough to produce 3 oz of pressure.  Flow rate is dependent upon pressure.

There are 2 methods

explained on page 2.  The Noel Method and the Simple method.  The Simple Method is explained in the last paragraph.  They did all the math for you.  There is nothing else to figure.  That is the secret, that you and I, donated 10 bucks to charity, to hear.  Well worth it, when I think about all the fuel I did not burn this winter. 

Not sure why

the Gorton #2 only has a 1/2" tapping. But that obviously doesn't hurt its capacity!

run it back along the main

For the vent that is at the end of the main I would come out of the main and go back along the main 15" or so and the use an elbow, short nipple and a 3/4 to 1/2' reducer to mount the vent on. Use 3/4" pipe for as much as you can in case you want to add more venting later, 3/4" pipe has 2-1/2 times the area that 1/2' pipe has.



For the one that you might not have enough room, can you use an elbow to get clear of any obstructions? just make sure you have positive pitch so water can drain back. If the height is really short you may have to see if you can pipe in a antler with multiple Gorton #1's; they are a lot smaller than the #2.



Bob