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# how to calculate resistance (head?) for a 180 degree turn return 3/4" pipe

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Member Posts: 48
Like @EdTheHeaterMan posted in this photo, how to model the resistance for these 180 degree turns of the copper pipe? What happens if this is a PEX pipe? Is there some specification somewhere I can look at?

Many thanks.

• Member Posts: 23,426
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Same as two close 90s, or close enough as doesn't matter.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 22,251
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Call it 2- 3/4 90 ells
Usually if the sweep is a 4" radius or more in 1/2" pex it is not considered in head calcs.
8D typically, so 3/4 copper or pex would be a 6" radius
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 48
edited April 18
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I see. So, with a 6" radius for 3/5 copper, I would need the supply pipe 1 ft off the floor to give the 6" turning raidus. Do I interprete it correctly?
• Member Posts: 3,328
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Hi, My understanding is that if the radius of the bend is five times (or more) the diameter of the pipe, the water no longer knows it's changing direction and the friction loss is only equal to the length of the pipe.

Yours, Larry
• Member Posts: 48
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Thanks @Larry Weingarten @hot_rod @Jamie Hall for answering. So, if I do not want 1 ft high baseboard off the floor, I will have to curve the turn with smaller radius, I just model it as 2 90 degree elbows, which adds 2 ft head each with the total of 4 ft head, right?
• Member Posts: 23,426
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Got it
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 22,251
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long sweep copper ells would have a lower pressure drop. You may find charts with the EL of longer sweep ells. I suspect the sweep ell may be 1/2 the flow resistance of the typical copper ell?

I doubt you would get enough of a sweep radius inside a typical fin tube enclosure to get 0 pressure drop. If that is where you are headed?

I don't remember where the radius number comes from. Either the Copper Tube Handbook bending section 4, or maybe the REMS tube bender tech sheet. I don't know there is an exact multiplier??
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 147
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You might have enough space to do this with a large enough radius:

• Member Posts: 1,065
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iexpl said:

Thanks @Larry Weingarten @hot_rod @Jamie Hall for answering. So, if I do not want 1 ft high baseboard off the floor, I will have to curve the turn with smaller radius, I just model it as 2 90 degree elbows, which adds 2 ft head each with the total of 4 ft head, right?

The copper 90's do not add 2 feet of head, they add 2 feet equivalent pipe length. Make sure when you are adding the fittings that if the value of the table you are looking at says "equivalent length" you are not counting that as feet of head or you will end up with a massive pump
• Member Posts: 22,251
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like this
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 9,735
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What are you trying to accomplish? Unless you are dealing with a monoflo system or something only very rough calculations are usually necessary especially with adjustable ECM circulators.
• Member Posts: 48
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I am trying to get rid of the monoflo Tees by connecting pipes directly due to pepetual imbalance of the monoflo system. @mattmia2

@hot_rod thanks for the illustration.

@GGross thanks for the head up calculation for the pump. I am a layman and need some understanding of this.
• Member Posts: 9,735
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use regular tees and put a balancing valve in the main between the tees then you can use the balancing valve to effectively make the monoflo orifice whatever size you want.
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@mattmia2 are these balancing valves self adjustable? This is a rental unit and no one is there to adjust the system :-(
• Member Posts: 9,735
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You only have to do it once. I don't see what you're going to do with math that doesn't involve 100 inputs that are pure guesses.