to split a pipe loop

ralman

I can't find anything that really spells it out. The only thing I see in writing is size the common return to accomodate the combined flow. Great! Now, How about the supply? If I split a 3/4 zone and expect 4gpm flow in both sides, Would I not upsize the pipe to 1" up to the split? If not, please explain why, It is driving me nuts.

Brad White

Division

Typically, when I hear someone speak of splitting an existing loop, the flow is divided in some proportion, 50-50, 60-40, whatever.

The common return would of course be sized for the flow encountered.

Now, if I could divide my piping and multiply my flow, I would really have something!

Not sure what you say is "driving me nuts" but that steering wheel below your belt may be a contributor. Remove it and see.

ralman

Thanks, Brad

My piping arrangement had a 1.5" common supply to the split, which was 1.25" back to the common return and also from there to the boiler. I had changed that common return to 1.5" Just thinking that was the right thing to do. So, for example, a 3/4 loop with 4 gpm flow is split. Assuming the resistance is equal on both sides of the split, 2 gpm of flow is now occurring on both sides of the split. Common return can still be handled with a 3/4 pipe. What if I wanted to keep both sides of the split at 4gpm? If I use 1" pipe for a common supply and 1" pipe for a common return would that do it? What if I only had 2gpm of flow to start with, equally split I will fall below the 2FPS rule. It seems there is little written information about the design procedures for using these methods. Somebody should write a book, or add it into their existing book on their next update. It seems like it would be a very useful information.

Brad White

Design Procedure

Using 1" as a common size to split or conjoin the 3/4" branches should work just fine, Ross. In fact, our office standard is that any two 3/4" lines will be fed by no less than a 1". It may be conservative but painlessly assures enough reserve for future modifications, at least in our commercial and institutional work.

The "2 FPS" velocity rule does not concern me too much so long as the ability to vent high-point air is there. Keeping a minimum velocity is to keep entrained air moving to a point where it can be removed elsewhere such as by purging or an eliminator.

Consider when you retrofit an old gravity system- If you get 0.5 FPS to 1.0 FPS nearly anywhere you are doing well.

Just as the Queen of England goes to the bathroom, it happens but nobody talks about it.

As for written information, it has all been done- pipe size, flow and velocity principles are there to be applied. I would not lose sleep over it. Leave that to other concerns.