2" with sweep elbow or 2-1/2" with 90 degree elbow

[work4rus]

I am changing all the plumbing in my pool. The equipment details are below, but basically all accept either 2" or 2-1/2" size pipes. The underground line runs will be 2". My question is - for above ground plumbing, should I use 2" with sweep elbows or 2-1/2" with 90 degree elbows? (I do not consider 2 1/2" with sweep because I can't find the parts and if I would, it takes too much space and is probably an overkill. )

 

[Catanzaro]

I would use the 2" sweeps as you will have less resistance. When the installer added the heater and SWG, he installed sweeps instead of 90* elbows to lower resistance. Some bends had to have 90* elbows. Every little bit helps. I know that before heater and SWG, my pressure was at 12 psi and after 22 psi, with 2" plumbing. Big change in flow, but still works well.

 

[work4rus]

Thank you Catanzaro! I agree that 2" with sweep elbow is low resistance. But how do you know that it is less resistance than 2-1/2 with 90 degree? Maybe because of a much greater 2-1/2 size the flow would be better even with 90 degree?

 

[JoyfulNoise]

Thank you Catanzaro! I agree that 2" with sweep elbow is low resistance. But how do you know that it is less resistance than 2-1/2 with 90 degree? Maybe because of a much greater 2-1/2 size the flow would be better even with 90 degree?

See here - PVC - Friction Loss in Fittings and Equivalent Length

I'm not sure they make 2-1/2" 90 deg elbows. But you can see that the difference between a 2" sweep and 2" elbow is about 3-ft of equivalent pipe length. Two (2) 2-1/2" 45 deg fittings would be roughly equivalent to 2" sweep in terms of equivalent pipe length. You would then have to compare the relative head loss for each type of pipe diameter...

At the end of the day, the pipe diameter that you use has a much greater effect on head loss than the kinds of fittings unless you plan to use an excessive number of fittings...

 

[work4rus]

Very interesting table. Based on it, 2" sweep is loosing the equivalent of 5.7 ft and 2-1/2" elbow - around 10 ft (yes, they make them). Still, my knowledge is not enough to understand what is more efficient for a relatively straightforward above ground equipment plumbing.

 

[JoyfulNoise]

Very interesting table. Based on it, 2" sweep is loosing the equivalent of 5.7 ft and 2-1/2" elbow - around 10 ft (yes, they make them). Still, my knowledge is not enough to understand what is more efficient for a relatively straightforward above ground equipment plumbing.

This page shows some more advanced calculations with an Excel Spreadsheet.

Equivalent Length Method - Calculating Minor Pressure Loss in Piping Systems

Just remember that when comparing "equivalent lengths of pipe" the information presented means that a 2" sweep is the equivalent of 5.7ft of 2" pipe which a 2-1/2" elbow is the equivalent of 10ft of 2-1/2" pipe. So in order to figure out the head loss, you need to make sure you're using the right pipe size.

Honestly speaking, any loss of efficiency is going to be negligible for a few fittings here and there. There way more head loss in the system from filters, heaters, etc, such that it will swamp out any gains by using a few sweeps versus a few elbows.

 

[mas985]

Also, sweeps tend to be DWV rated and not pressure rated so they are usually much thinner walls and shorter glue area. I would not use them on my plumbing.

But I agree with Matt, there is very little change to efficiency when looking at the total head loss.

 

[work4rus]

Mark, using DWV in the pool would be an obvious mistake. They have Sched 40 sweeps like here

 

[mas985]

You would be surprised at how many people end up using DWV fittings. But I still don't think it is worth the effort.

 

[work4rus]

At the end of the day, the pipe diameter that you use has a much greater effect on head loss than the kinds of fittings unless you plan to use an excessive number of fittings...

At the end of the day I gave up trying to calculate the difference. After comparing pipes and fittings at a store - it was apparent that 2-1/2" feels so much bigger than 2". So I thought that Matt is right, the diameter just have to make a lot of difference. So all above ground equipment will be done with 2-1/2" pipes with 90 degree elbow. Thank you for the help!

 

[mas985]

2.5" fittings have half the head loss, at the same flow rate, as 2".

 

[work4rus]

2.5" fittings have half the head loss, at the same flow rate, as 2".

I wander why not everyone does 2-1/2" above ground

 

[mas985]

Re: 2" with sweep elbow or 2-1/2" with 90 degree elbow

Because there is only a little benefit especially on lower speeds of a vs or two speed.

Plus much of the head loss in a pool is due to other than pipe and fittings.

Forgot to mention that at a fixed rpm the pump motor actually draws more power with lower head loss. More flow is delivered but that rarely makes a difference to run time. With a vs you may be able to reduce rpm some.

 

[JoyfulNoise]

Re: 2" with sweep elbow or 2-1/2" with 90 degree elbow

Forgot to mention that at a fixed rpm the pump motor actually draws more power with lower head loss. More flow is delivered but that rarely makes a difference to run time.

I have direct experience with this. My waterfall is attached to a 3HP WhisperFlo pump and originally there was only one valve to split the flow between the open pipe in the waterfall and a separate wall return. I had to add a second shutoff valve to choke off the pump or else the flow rate would be so high that the pump would cavitate (true cavitation). So I essentially had to add head loss or else the pump would rattle itself to pieces. One of the many updates I need to do is to replace that ridiculous pump with either a true waterfall pump or a small variable speed pump. Or maybe buy the latest version of the IntelliFlo and swap my older IntelliFlo over to the waterfall.

It was a very real world and constant reminder to me that proper plumbing design, as well as having an appropriate amount of head loss, is important.