Main vents

ToddB

I'm planning to install my main vents and have a few questions.  I have calculated the air volume in the mains (both about 2.6 CF - mains are same diameter and about the same length).  Right now both of the existing vents are different - one is a Gorton 1 and the other is a VentRite - I am not sure of the model.  I was planning on installing new Gorton 1 vents.

I am looking at the Balancing Steam Systems book that I recently purchased that has venting capacities, but I am not sure what the columns 1 ounce, 2 ounce, 3 ounce mean at the table headings for the vents.  Why provide three values for system pressure? 

BobC

They are too small

If each main has 2.8 cu ft then you need at least one Gorton #2 on each of those mains and maybe two. The Ventrite (probably a #35) has about 40% the venting capacity of the Gorton #1 and the #1 has about 30% the capacity of the #2.



You want to get that air out of the mains fast.



Bob

crash2009

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.  

ToddB

Still confused

Why is 3 ounces of pressure used in the examples on page 2?  I thought a boiler would typically make 16 ounces of pressure?

Dave in QCA

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.

ToddB

Got it

But if I were to install Gorton 2 vents they are only 1/2".  Would this in any way impact what I am doing?  For instance, if you were to consider 1/2" open pipe at 1 oz.  pressure, then you would have 2.6 cfm.  The venting rate of a Gorton 2 is 1.1 cfm at 1 oz.  So two vents per main would be sufficient.  Or would I still consider the 3/4" tappings that I have? 

crash2009

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. 

Dave in QCA

The method I used....

The method I used for determining the vent needed is to calculate the volume of the steam main and then figure that it needs to have enough vent capacity to get steam to the end of the main in 2-3 minutes.  One Gorton #2 would do that for you.

Steamhead

Not sure why

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

ToddB

How to pipe

I think that I am going to start with one Gorton 2 at each main.  Right now the system heats quickly, so these new vents can only help.  I can add more in the future if needed. 

Considering that I have 3/4" main tappings and the Gorton 2's have 1/2" tappings, what would be the best way to pipe the vents?  Carry 3/4" pipe to the end and reduce to 1/2" at the vent?

Currently the vents are screwed right into the mains.  One of the vents is located right at the end of the main adjacent to the elbow for the return.  I was planning on raising both vents away from the mains, but I am goint to have fit issues at one location (not the one located adjacent to the return elbow).  Does it make sense to install antlers with single vent connections at each location to slightly raise the vents at both mains?

BobC

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

crash2009

Here are

 a couple piping examples Todd.  The menorah is the preferred way.  Whichever way you choose, make sure the condensate can drain back to the main.