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isolation flange

Joe D.
Joe D. Member Posts: 19
I ordered a set of these Taco brand 1-1/4 inch threaded isolation flanges to plumb in a pump in my heating system.

After I get them I notice that although they fit that size of pipe, I see that at the ball valve area, they are reduced down to a 3/4 inch diameter.

Now, what good it does for me to make my primary loop inch and a quarter when I end up with two- three quarter inch restrictions in the line?

I am pondering the idea of buying 1-1/4 ball valves and silver soldering them to some flanges, and making my own compact isolation flanges.

What say ye?


  • Paul Fredricks_2
    Paul Fredricks_2 Member Posts: 35

    Even an 1-1/4 ball valve is reduced down. Unless you need an awfully large amount of flow the reduced sized at the isolation flanges shouldn't be an issue. Yes, you would get more flow if everything was 1-1/4 ID, but remember too that the inside of the circulator is smaller also.
  • Darin Cook_2
    Darin Cook_2 Member Posts: 205

    Look inside the "hole" of the pump and see what size it is. Notice how the pump can be bolted to many different size flanges. The pump overcomes hydraulic resistance. Which is why you use a pump sizing chart to tell you if it will work in your application. Those Taco flanges will work just fine for you. You just need to double check the pump sizing. I hope this helps and happy piping.
  • Joe D.
    Joe D. Member Posts: 19
    Very well, then....

    Good enough explanation for me.
  • Tony Conner
    Tony Conner Member Posts: 549

    ... these valves are so short in length, the pressure drop across them, and the impact on flow will be the square root of nothing. Think of piping systems as chains, and every component - straight sections of pipe, fittings, valves, etc as links. The outlet pressure from one link is the inlet pressure to the next. Specialty bits like pumps, control valves, check valves, etc will routinely be smaller diameter than the properly sized pipe they're connected to. The pipe is normally larger diameter, because it's so much longer, in comparison.
  • Kevin O. Pulver
    Kevin O. Pulver Member Posts: 380
    It was a good question Joe

    I've wondered myself at times. The water will just have to speed up momentarily to maintain the same GPM flow rate at this restricted point. It's a very short point though, so no problem. Now if that ball valve were several feet long or more it would get worse in a hurry. Imagine this: How fast can you blow air through a 1/4" drinking straw? How about a 1/4" hose 100 feet long? (much harder) Now how fast can you blow air through a hole in a 1/4" nut or flat washer? (Much easier) It's the same size restriction in all three cases, just a matter of the LENGTH of the restriction. And the length multiplies the resistance. To borrow loosely from an illustration from Dan, imagine a 4 lane freeway with an accident where it narrows down to 1 lane for 10 feet. Imagine the traffic getting through. Now imagine the 1 lane is a construction zone that continues for 2 miles. See the difference?
    Hope this helps. Kevin
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