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# Compressed Air Loop - 1.5x capacity multiplier...2

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## Compressed Air Loop - 1.5x capacity multiplier...

(OP)
Hello everybody.

Looking for some clarification or input on an engineering theory. If feeding a "loop" from two sources, you can effectively add 1.5x to your capacity.
In the example below, there is an 8" compressed air main from the compressor building into the plant. From this 8" line, there are (2) 4" sub headers. Let's say (for easy numbers0 that each of the 4" sub headers each have a carrying capacity of 1,000 SCFM.

Does tying these (2) sub headers together in essence turn the 4" loop into (1) 4" sub header with a 1.5x capacity multiplier for a total of 1,500. OR would you add the total of the (2) 4" sub headers together (1000+1000) and then add the 1.5x multiplier for a SCFM capacity total of 3,000?

Any input or literature that can be provided would be very helpful and much appreciated.

Replies continue below

### RE: Compressed Air Loop - 1.5x capacity multiplier...

I think it's more that one user in a loop could use 1.5 times the "capacity", but that doesn't impact the total capacity in the 8" loop which remains at 2000.

But "capacity" is a vague term without know what the limit is

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Compressed Air Loop - 1.5x capacity multiplier...

Theoretically you could now deliver 2000 to any point in the entire system, whereas before only 1000 was available to any one consumer at any point on a branch, although you could have up to 2 consumers of 1000 SCFD, if located on different segments. Any larger consumer (>1000) would have had to be located on the main.

With the loop modification, you can distribute 0 to 2000 anywhere and everywhere and your pressure drop at 2000 SCFD will be about the same, even though you effectively doubled the distribution capacity to any point in the loop.

3000? Not necessarily. You have already doubled the distribution capacity to any point keeping about the same pressure drop, but if you can increase the acceptable pressure drop, some more capacity is theoretically possible.

Defining the max operating pressure and the minimum pressure acceptable to consumers and the lengths of the pipe segments could lead to the answer you are looking for.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

### RE: Compressed Air Loop - 1.5x capacity multiplier...

There's a few things in issue here I think.

1) what you drew isn't really a loop fed from two sources as part of your "loop" is actually the header pipe, so a different size.
2) It must depend on where in the loop the two inputs are and where the offtakes are.
3) Where is this "theory" stated? What conditions does it list as being applicable?
4) Maybe what it means is that if you have a loop fed from one source then the capacity is 1.5 times what it would be if there was no loop, only a single connection to the user? I saw this in an electrical ring main where e.g. if you have a wire rated at 20 A in a ring main, you can feed 29A into it for long periods. Is there where the 1.5 comes from?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Compressed Air Loop - 1.5x capacity multiplier...

The 8" header has effectively no pressure drop at 2000cfm if <= 2000 ft long.
It is no longer a "header", but now in the loop. It becomes a loop, with a feeder and one dead end Branch. Pipe size in a loop can be different. No problem. It makes feed from the header into the remainder of the loop at almost the same pressures.
1.5? No. Pressure drop in the loop remains nearly constant at 1000 cfm feed from both sides = 2000 cfm total delivery, so with the same 1000 cfm in each pipe, pressure drops and flows will be the same.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

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