main vent questions

MJ_in_centralPA

I'm planning on putting in a main vent on my neglected unvented main steam line which is <strong>68ft long 2 1/2".</strong>

My father in law was planning on coming down to weld on a<strong> 3/4" tap</strong> 15 in after last riser and I was planning<strong> 2-3 maid o mist main vents menora style</strong> (based on my cu ft calculations)

Sound appropiate. <strong>Do I need a 3/4" tap</strong>? Thought i read some where that 1/2" tap is too small to vent my line in ~3minutes.

Thanks

BobC

A LOT of MOM's

It looks like that 68 ft of 2-1/2 pipe has 3.9 cu ft of volume and a Maid o Mist #1 is rated for 0.33 cfm at 1oz of pressure so it will take a few of them. It might cost less to use Gorton #2's which are rated at 1.1 cfm at 1oz of pressure. Gorton #2's have a 1/2" male thread so you will need reducers if you build the piping with 3/4" and they are pretty large - make sure you have room for them



A 1/2" open pipe is good for 2.6 cu ft according to my chart, 3/4 would handle a lot more but I'm not sure you will need it but if your going to the trouble of welding something up why not? Just make sure you new tree will let any water flow back into the main so the vents don't spit or start acting like fountains.



Bob

Steamhead

You're thinking of 3-inch pipe

2-1/2" has .030 cubic feet per running foot. So that main has 2.04 cubic feet. Two Gorton #2 vents are the right choice here, and a 3/4" tap as proposed will work fine.

MJ_in_centralPA

maid of mist

thanks so much guys for your quick responses

could I use maid o mist? what is the rating on maid o mist ?0.33cfm at 2oz?

what is gorton #2 cfm at 2oz?

maid o mist is much cheaper than gorton#2, how many maid o mist would i really need 6 maid o mist #1's?

crash2009

cfm comparison

Maid O Mist #1 is 0.590 cfm @ 2 oz.

Gorton #2 is 1.750 cfm @ 2 oz.

Three times the vent for only twice the price.



Here is a shortcut to some more information (pictures and a video)  http://www.gwgillplumbingandheating.com/webapp/GetPage?pid=415

Steamhead

I prefer

to size main vents at 1 ounce. At that pressure the Gorton #2 will vent 1.1 CFM. 

crash2009

Why is it preferable

 to size the vents at 1 oz.?  Sure does makes the math easier.  2.04 cu ft needs 2 vents.  3.06 cu ft would need 3 vents?  4.08 cu ft would need 4 vents?  5.10 cu ft would need a 1" tapp?  Or am I not looking at this correctly? 

Steamhead

If you size main vents at 1 ounce

riser vents (if used) at 2 ounces and radiator vents at 3 ounces, the steam is more likely to fill the mains first, risers second and rads last. 

crash2009

Thanks

I had forgotten.  You explained that to me before.