Flanged piping system

[PQ2]

One-pin vs. a two-pin flange?
A contractor indicated that they would rather have a two-pin flange rather than a one-pin flange when connecting to a piping system that had a 20-inch Megalug flanged conection.

 

[jcfoley]

Any chance that he means One holed vs Two holed?

 

[PQ2]

Yes there is. Can you tell me what a two-holed vs. a one-holed flange is?

 

[jcfoley]

This is a positioning of the flanges when they are installed. It has nothing to do with different types of flanges. A "One holed" flange has a bolt hole aligned at the top of the flange. A "Two holed" flange is installed so that two bolt holes straddle the pipe centerline at the top. I have tried to lay this out in a diagram below but it is not too great as I cannot get them to line up perfectly. The O is a bolt hole. The + is the center line of the pipe.

O O O

+ +


A flange that is installed "two holed" is easier to work with as the gaskets are installed.

 

[TBP]

On horizontal pipe, "two-holing" a flange means that the bolt holes are oriented such that there won't be one hole at the 12 o'clock position, but rather a pair of holes, that are oriented such that the top two bolt holes are in the same plane. This is easily done with a level. If you look at something like a flanged gate valve (any manufacturer), you'll see that the bolt holes are oriented to match this configuration. If you didn't have this convention, it would be more difficult to align things. You'd look down a piping run, and valve spindles would be pointing off in all kinds of goofy points of the clock. It also lets valve manufacturers make the valve bodies with a shorter face to face dimension than would otherwise be possible. If flanges were one-holed, they'd have to leave space between the flange and the bonnet to get fingers and wrenches in there to do up the bolts. This can be tight enough, even with two-holing.

 

[PQ2]

Thanks, your answers are just what I need.