Can a pair of flanges mate directly to each other?

Gordan

Or is there some sort of asymmetry between the flange on a pump and the mating flange affixed to the pipe?

Would that be a good alternative to unions for service (dis)connections on the boiler and the boiler circuit of an indirect tank?



With flanges being comparable in cost, and able to mate (say) 1" pipe on one end with 1 1/4" pipe on the other end, is there any advantage left to using unions?

Charlie from wmass

I can only say

I think it looks kind of cobbish. I can think of no mechanical reason except a possible noise issue as there is no taper to the transition between sizes.

Gordan

Yes, I was thinking the same, but...

...this is commonly done with circulators.

Bob Bona_4

I've done

it occasionally on some near boiler piping improvements/adding new zones where I know the boiler is going to be changed in the soon future. Usually where I've moved a circ to the supply side of the piping and I leave the return flange intact. I'll use a new mating flange and stub to jump to the existing return piping.

But I wouldn't do it as a permanent thing. The flange gasket will eventually leak.

I would use unions if you want a proper disconnect point.



 

Gordan

Thanks!

Do the gaskets leak eventually on flanged circulators, too? I'd be inclined to be more concerned about those connections leaking, say, on an internally mounted flanged circulator such as the one inside the PS 110. Not only is such a leak hidden from view, but it also happens to be pretty near electronics.



If unions are superior to flanged connections, how come union-attached circulators are so rare? Don't get me wrong, I'm not challenging your answer (having asked for it), just trying to understand the reasons we have all these types of connections.

Mark Eatherton

I'm with Bob on this one...

You COULD use flanges, but.... and there's a butt in every crowd...



We're talking a two point compression factor, versus 4 points with the typical piping flange, or 360 degrees of compression for a ground joint union.



The trick to unions is lubrication and sealant. Lubrication on the inside of the large nut, to keep it from sticking and locking and sealant (permatex or whatever) to seal the mating surfaces. (I know, I know. The code doesn't allow for the use of sealants on the mating faces of a union, but the code authorities don't have to work with these crap unions from China...) Even American Unions don't make up well.



Flange gaskets do stop water, for the most part, but they DON'T stop oxygen ingression.



That reason, coupled with eventual hardness due to all the oxygen passing through them, the gaskets will fail. Which then leads to leakage, which is never a good thing.



Why ask for trouble. Personally, I don't put unions on anything, unless the item comes with unions on it. It invites unqualified participation from people who view unions as "Velcro"...who really have no business messing with the equipment. If you don't know how to cut and thread pipe, maybe you shouldn't be messing with the pipes. :-)



It's not rocket science, but it CAN blow up in your face.



Be safe out there.



ME

Bob Bona_4

yes they do.

But they are a necessary evil. Why create another leak point? And, yes, who can be crazy about concealed flanges by PCB's? However, at the *annual* service intervals, those joints are exposed for inspection. I haven't seen a sudden gasket failure yet, but many, many, MANY neglected corroded flanges from bad gaskets that aren't leaking yet, and the last guy there chose to ignore them or wrongly put them on the low priority list...

Union circs..hmm. Think about universal compatibility. Who would buy and stock a union circ? You would have to have 95% or more of all boilers out there to have one half of BOTH sides of the unions already installed on the system piping to make it practical. Otherwise, a routine circ change would turn into some serious wrenching/sweating/swearing as you have to modify things to accept. 

The standard 3 1/2" +/- spread by 71/2" +/- gap circ flange dimension has worked pretty well for the last 50+ years.. 

You have some tolerances between flanges whereas good luck spreading a unioned gap for circ install on some jobs.



Webstone would have to R+D union ball valves, etc. 

Gordan

All makes sense so far.

So how do you feel about the proliferation of compression fittings that employ gaskets and o-rings? This would be pretty much every radiant manifold out there. R20, BSP, etc. Them Europeans like their gaskets, and we like them Europeans!

hot_rod

union circulators

are becoming more common as we see more solar pump stations on the market from European sources. Once you have tried them you will see how much easier they are to install and un-install. No more rusted bolt and nuts or prying the flanges apart to install the circ.



In many cases that same "green" gasket couples fittings, manifolds and many hydronic devices.



The gasketed connection takes all the "crappy ground joint" issues out of the equation.



We've used those gaskets for years in pressure reducing valve union connection, they stick the surfaces together the first time they get wet, but still allow for easy removal. No pipe dope is needed and the fittings need be a bit beyond finger tight.



Fel-Pro is one of the gasket manufacturers and they have plenty of experience with high pressure and temperature fluids.



hr

meplumber

Just a side note.

Mark brought up a good point.  Oxygen.  Not all gaskets are the same.

BUNA, EPDM, Felt, CorPro, the list goes on forever.  In the industrial world, gasket material is spec'd with the flange characteristics.  The Europeans also spec the gasket or O-ring material.  BUNA has certain parameters, as does, EPDM.  They are chosen specifically for their heat, pressure and whether the system is "open" or "closed" loop.

If you must use a flange, ASME recommends at least a 150 lb 4-hole flange for permanent mating.

Just some food for thought.