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 Proper vent pipe size on 20K Gas Fuel Tank		 Bookmark and Share
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CORKNUTZ69

USA
72 Posts
Posted - 05/11/2012 :  13:45:48  Show Profile  Reply with Quote
Little debate going on, want to see what you guys think. What do you all go by?

bigbadjohn

Canada
2166 Posts
Posted - 05/11/2012 :  14:44:50  Show Profile  Visit bigbadjohn's Homepage  Reply with Quote
In ground or underground? Material? How big is the fill pipe? What's the designed flow rate of the pump pulling fuel out of the tank?

It's a lot easier to under vent than over vent.
Don't learn safety by accident.
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CORKNUTZ69

USA
72 Posts
Posted - 05/13/2012 :  08:14:33  Show Profile  Reply with Quote
Underground, fiberglass tank, 4" fill, F.E. Petro 2 ho sub.
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hardworking

USA
506 Posts
Posted - 05/13/2012 :  08:30:29  Show Profile  Reply with Quote
A few decades ago I was taught that the "general rule of thumb" was the vent should be at least 1/2 the size of the fill. 4" fill, 2" vent. 3" fill, 1.5" vent. Like BBJ said, nothing wrong with going above and beyond.
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Glenn Farmer

USA
308 Posts
Posted - 05/13/2012 :  21:03:35  Show Profile  Visit Glenn Farmer's Homepage  Reply with Quote
Some will tell you that the vent needs to be the same size as the fill but how many 4" vents have you seen? Most of the UST vents we install are 2" unless we manifold two gasoline tanks then go up to 3". Maybe Cherokee or Whit has specific knowledge of vent sizing requirements?
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whittingtonm

USA
1079 Posts
Posted - 05/14/2012 :  08:50:20  Show Profile  Visit whittingtonm's Homepage  Reply with Quote
I'll have to do some research. I don't see anything in the regs in a quick look. There may be a practical limit for sites with Stage 2/Phase 2 or Stage 1 required under the federal rules. That is the requirement to use an approved Pressure/Vent Valve. The Husky 5885, for example is listed only in a 2-inch model and a 3-inch model, so a 4-inch vent pipe add anything. But that still doesn't explain how to select between 2-inch piping and 3-inch piping.

Might be in a CARB order, though. Also might be in tank manufacturer recommendations, which I did not check yet.

Tank Genie?
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tankgenie

USA
189 Posts
Posted - 05/15/2012 :  11:30:48  Show Profile  Reply with Quote
Best reference would be NFPA Section 23.6 Normal Venting for Underground Storage Tanks Section 23.6.2 Vent piping shall be sized in accordance with
Table 23.6.2. but shall not be less than 1.25 in. (32 mm) nominal inside diameter. Table 23.6.2 has GPM / Length of Pipe / Diameter of Vent Cap listed. It says for up to 100 gpm, 1.25" diameter for up to 200 feet of vent piping, including 7 Ell fittings. 2 HP FE Petro shouldn't exceed 100 gpm.
"Resident Googler"
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tankgenie

USA
189 Posts
Posted - 05/15/2012 :  11:32:47  Show Profile  Reply with Quote
Note: 1.25" diameter would be the minimum; If its a Stage 2 or Stage 1 site, you can't do less than a 2" as noted by Whittingtonm due to the availability of CARB approved models only being 2 and 3 inch.
"Resident Googler"
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whittingtonm

USA
1079 Posts
Posted - 05/15/2012 :  14:14:56  Show Profile  Visit whittingtonm's Homepage  Reply with Quote
tankgenie, Thanks very much! It took me a while to get to the NFPA 30 section you cited. (I keep NFPA 30A in a paper copy on my desk, but NFPA 30 is filed away electronically.)

By the way, I didn't see anything in one tank manufacturer's installation manual about vent pipe sizing, except to be sure it was "adequately" sized. PEI RP100-11 says the same thing. NFPA 30 seems to be the best place to go to answer this question.

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tankgenie

USA
189 Posts
Posted - 05/15/2012 :  14:20:31  Show Profile  Reply with Quote
Woops...forgot to Say NFPA 30, Section 23.6. Thanks for connecting the dots Whit! I try to purchase all the regulations we have to follow in adobe PDF electronic format which helps keyword search when I'm in a crunch for time.
"Resident Googler"
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CORKNUTZ69

USA
72 Posts
Posted - 05/16/2012 :  19:47:52  Show Profile  Reply with Quote
Thanks guys
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whittingtonm

USA
1079 Posts
Posted - 05/17/2012 :  16:18:22  Show Profile  Visit whittingtonm's Homepage  Reply with Quote
Thanks for posting that. It was an interesting question that I didn't realize was so difficult to find the answer to.
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Glenn Farmer

USA
308 Posts
Posted - 05/18/2012 :  18:57:43  Show Profile  Visit Glenn Farmer's Homepage  Reply with Quote
You just have to love the knowledge and expertise available here. Speaks very highly of the folks in our industry. Thanks Whit & Tankgenie!
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whittingtonm

USA
1079 Posts
Posted - 05/21/2012 :  07:27:27  Show Profile  Visit whittingtonm's Homepage  Reply with Quote
Yes, Thanks, Tank Genie, for having the answer!
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bigbadjohn

Canada
2166 Posts
Posted - 05/21/2012 :  18:49:17  Show Profile  Visit bigbadjohn's Homepage  Reply with Quote
A 2 hP FE Petro variable speed STP is rated at 110gpm max flow so you're going bigger than the bare minimum 1-1/4".
Don't learn safety by accident.
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dgbrickley

USA
12 Posts
Posted - 05/25/2012 :  12:33:44  Show Profile  Visit dgbrickley's Homepage  Reply with Quote
UL 58 - 2.5"-3"
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