splitting flow for 4 returns (bullhead vs branch tees)

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Diver

Diver

0
May 5, 2011
482
South of Boston
Hi!

I'm adding solar panels to my pool, so I need to redo some of the return side plumbing. I have 4 returns, and 2 of them are short and two of them are long (distance from the pump).

Originally I planned on going with balanced split with 3 bullhead tees (top to bottom flow on the pic):

1.jpg


Well, it turns out to be too wide for my project and then I learned that bullhead tees are not very efficient and produce a lot of head.

So one of the alternatives is to replace 2 bullhead tees with 2 branch tees that are less restrictive:

2.jpg


I like this since it's still have some symmetry and I can attach longer returns to straight runs and shorter ones to branched runs balancing out the flow.

There is also a possibility to replace the top bullhead with a branch tee as well or even use the cross like I have right now (ignore the plumbing mess - this is what I'm redoing):

3.jpg


But in this scenario I'm not sure which return to attach to what position and perfectionist in me is bothered that. In the last pic, I would imaging that the most straight run is the least restrictive, but how about the rest?

I know, I'm overthinking this :)
 
You have to consider the total head loss of each path from the first branch point all the way out of the pool return including the eyeball if they are different. If you don't take into account the pipe lengths, the flow will not be equal no matter what you do with the fittings.

Do you actually see much of a flow rate difference in the paths as it stands now? You really shouldn't. A fitting or two should not have much of an impact on flow rate differences.

Also, why do you care if they are a little different?
 
mas985 said:
Do you actually see much of a flow rate difference in the paths as it stands now? You really shouldn't. A fitting or two should not have much of an impact on flow rate differences.

Also, why do you care if they are a little different?
Click to expand...

I don't have any meaningful differences in the flow. But since I'm redoing the plumbing, I want to help any potential difference :) As I mentioned before, it's a perfectionist in me that is contemplating all this. Realistically I realize it's not gonna make huge difference.

Thanks everyone for your replies.
 
Well, due to space constraints, I ended up with all branch tees and no bullhead tees (ignore existing main drain line):



What is interesting is the difference in clean filter pressure. It went from 8/9 psi to 6 psi. It's combination of replacing 1.5" fittings with 2" fittings and rework of the tees that made the difference. I just didn't expect such a big drop.

What is more interesting is that typically upon opening at the beginning of the season (i always open green due to too may holes in the cover) I cloug the filter in a matter of few days going to blue from green. This time, 3 weeks after opening the filter psis are still at 6. Not sure if it has something to do with less restrictive output or not...
 
There is a big difference in fitting head loss when going from 1.5" to 2". It is about 63% less head loss in the fittings that were changed.
 

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I forgot to add though that each fitting contributes only a very small amount of head loss so it is surprising you saw so much of a change.

BTW, why is the one pipe labeled pump? Those are all return pipes correct?
 
another odd thing is that switching either main drain or skimmer off doesn't have any effect on filter psis anymore. switching solar on/off is the same.

it almost looks like my pressure gauge stuck and can't go above 6psi. it's relatively new though - this is either 2nd or 3rd season for it. i think i might have some old one laying around that i could try.

i also have a vaccuum gauge and a flow meter - i will try them this weekend as well. i'm curious about exact flowrate thru my solar panels..
 
If gauge goes to zero when the pump turns off, it is usually ok but try tapping it to see if it moves up further. But I agree, the pressure should change with a change in suction configuration unless there is something stuck in the impeller which would also account for lower than normal pressure.
 
since i will be putting the vacuum gauge into the wet end any way, I will check the impeller for obstructions. but without taking it apart, i will just check for obvious things...

looking at some data from past years, i was running about 60 gpm with 9 psi of filter pressure and 6.5in of vacuum. calculated 39 ft of head.

i had a flow meter earlier this year and i thought i saw numbers around 55 gpm, which now seems inconsistent with the new filter psi number.

i will check this weekend and report back...
 
The cheaper flow meters (Blue White) are not all that accurate and can have errors as much as 10% of full scale.
 
Well, I think mystery is solved and I'm pretty sure my filter pressure gauge is shut. And my impeller doesn't seem to be obstructed. I don't remember how easy it should turn, but it rotates smooth, albeit with some effort.

I installed the vacuum gauge and flow meter and took some readings. The numbers are below:

No Solar
Filter, PSI Pump Vacuum, in. Flow, GPM
MD+Skimmer 6 3 47
MD 6 12.5 40
Skimmer 6 8 42

Solar
Filter, PSI Pump Vacuum, in. Flow, GPM
MD+Skimmer 6.5 2 42
MD 6.5 10.5 36
Skimmer 6.5 6 38

As I was taking measurements and seeing such low vacuum numbers I though I got some intake blockage. Then I realized that if either skimmer or MD was blocked, the numbers for vacuum would be higher, not lower.

Seeing that filter pressure was staying put, I started tapping on the gauge and managed to move it to 6.5 and that's why for solar readings it went to 6.5. I got a bit more aggressive with it and moved it to 7psi.

Looking at this reading:

No Solar
Filter, PSI Pump Vacuum, in. Flow, GPM
MD+Skimmer 6 3 47

For my systems curve, 47 GPM is about 44 feet of head. 3" of vacuum for 44 feet of head, I believe results in about 14 psi of filter pressure. Which is probably close to what I have now after opening the pool and not backwashing the filter afterwards.

I'm a bit surprised with the vacuum reading. Looking at historical numbers for 47 GPM of flow I had lower psi (11-11.5) and higher vacuum (5.5-6), now with a new updated piping, the filter psi (calculated) seem to be higher and vacuum is lower. Does that mean that my return subsystem is more restrictive that intake one?

The changes that I made were reworked piping after the filter: 1.5"->2" and more streamlined fittings, check valve, solar 3 way valve and 1/2" eyeballs instead of 3/4" ones for all 4 returns. I believe it should be less restrictive than the old one.

I ordered and new gauge and get some readings from it when it arrives...
 
Return plumbing should always have more head loss than the suction and more than 2x is desirable. If it is too low, the pump could cavitate.

Remember too that if you are using the filter pressure, you have to make some corrections for the height the filter and also the plumbing between the filter and pump. Otherwise, the return head loss is too low. The flow rate spreadsheets I have make those corrections for you or you can measure pressure directly at the pump drain plug.
 

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