Sweeps vs hard 90s near suction port

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M

Myburneraccount

Well-known member
Apr 12, 2022
51
Dallas
Pool Size
10000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Truclear / Ei
My PB has his workers over to plumb the main drain (just in the shell). I don't believe these guys are actual plumbers as they didn't know some of the answers to basic questions I was asking.

It didn't seem like there was any thought put into using a sweep vs hard 90... more of what came out of the box or they could find on the truck.

On the pool side, what i noticed was the use of hard 90s right where the drain cover would go. Also used where to pipe transitions from floor to wall. Any concerns with headloss from this?

On the spa side (7x7), i was advised to put one floor drain and one bench. mostly hard 90s here except where you have back to back sweeps and one at the top. Seems like a lot hard turns but I don't want to make a mountain out of a molehill.

How much less efficient did my pool get or does it not matter? 2.5" suction lines.
 
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1poolman1 said:

Friction Loss In 2" PVC Fittings​

2" short radius 90 degree ell = 5.5 feet

2" 45 degree ell = 2.8 feet

2" long radius 90 ell (sweep elbow) = 4.3 feet

2" street ell (slip x spigot) = 8.6 feet
Click to expand...
Thank you. Does the location of the fittings or proximity to drain port matter?
1poolman1 said:

Friction Loss In 2" PVC Fittings​

2" short radius 90 degree ell = 5.5 feet

2" 45 degree ell = 2.8 feet

2" long radius 90 ell (sweep elbow) = 4.3 feet

2" street ell (slip x spigot) = 8.6 feet
Click to expand...
am I correct in concluding that while sweeps are better, they don’t necessarily make a big impact?
 
1poolman1 said:

Friction Loss In 2" PVC Fittings​

2" short radius 90 degree ell = 5.5 feet

2" 45 degree ell = 2.8 feet

2" long radius 90 ell (sweep elbow) = 4.3 feet

2" street ell (slip x spigot) = 8.6 feet
Click to expand...
The numbers are "equivalent" feet of pipe, not friction loss.

For example, (1) regular 90 is "equivalent" to 5.5 feet of straight pipe, but the actual friction (head loss) depends on the flow.

For example, at 90 gpm, the head loss is 5.2 feet per 100 feet of pipe.

So, the head loss from a regular 90 at 90 GPM is 0.052 (5.5) = 0.286 feet of head loss.

The friction head loss from a sweep 90 at 90 GPM is 0.052 (4.3) = 0.2236 feet of head loss.

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So, the head loss from a regular 90 at 90 GPM is 0.052 (5.5) = 0.286 feet of head loss.

If we use Lasco’s numbers, we get 0.286 - ((0.69)(0.286)) = 0.08866.

Or, 0.286 X 0.31 = 0.08866 feet of head loss for a 2.5" sweep 90 vs. 0.286 feet for a hard 90.

It depends on the values you have for the head loss “equivalent” feet of straight pipe for the hard 90 vs. the sweep 90.

The claim of a 69% reduction in head loss seems unrealistic.

Edit, maybe they mean that the head loss for a sweep is 69% compared to a hard 90, which is more realistic.

So, 0.286 X 0.69 = 0.19734 feet of head loss for a 2.5" sweep 90 at 90 GPM.

In any case, at flow rates below 6 feet per second, the head loss for a hard 90 is minimal and a sweep results in only minor reduction of head loss compared to the entire system.

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This chart shows 6.2 feet (equivalent) for a hard 90 and 3.3 feet equivalent for a 90 long radius sweep, which is closer to the Lasco numbers.

3.3/6.2 = 53%.

I think that a 2.5" sweep 90 is probably equivalent to about 4.3 feet of 2.5" straight PVC pipe.

4.3/6.2 = 69%, which is close to the Lasco numbers.

In my opinion, sweeps are preferable, but not absolutely necessary especially if you follow the water velocity rules.

For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.
1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138............184 gpm
4.0"........238.............317 gpm

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PVC Pipes - Equivalent Length and Pressure Loss in Fittings

Minor loss in PVC and CPVC fittings expressed as equivalent length of straight pipe.
www.engineeringtoolbox.com www.engineeringtoolbox.com
 
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Myburneraccount said:
I don't think my flow requirements are too high. Have a jandy 400k heater and jandy chlorinator. Filter is 150gpm max i believe. Max flow would be spa with 5 jets and judging by how the PB is building this pool, I assume I'm getting stardard jets (5) to max around 15-18gpm each.
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5 x 18 =90 GPM, so the 2.5" pipe is ok, but if you want to go above 90 GPM, the pipe should be 3".
 
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JamesW said:
5 x 18 =90 GPM, so the 2.5" pipe is ok, but if you want to go above 90 GPM, the pipe should be 3".
Click to expand...
Wow thank you for all the information. I really appreciate you breaking it down for me. I was having a bit of hard time following the numbers so I appreciate that you summed it up at the end.

For the spa drains, the PB is putting one in the bench and one on the floor. Inherently, the one going to the bench takes a few more twists and turns so I can't imagine that the suction will be balanced. But the second drain is there for entrapment purposes and less so for flow rates, correct?

Thank you again for the wealth of information.
 

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JamesW said:
Never put a drain/suction on a bench or anywhere people will sit.

You don't want people in contact with suctions at all.

I would do 4 regular main drains or 2 "unblockable" drains for safety if the drains are the only suctions.
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Is the drain near the seat not advisable for entrapment reasons or flow reasons?

What is an unblockable drain? Plumbing is already in, the pool has rebar, and we passed the initial partial plumbing inspection. Shotcrete scheduled for next week. Do i need to raise the flag here and pause everything? The first picture i posted with the back to back sweeps is the spa plumbing.

Thank you again.
 
A blockable main drain can be blocked by a person easily.

Blockable drains are typically smaller.

Unblockable drains are long or wide and cannot be easily blocked.

You have to look up the specific drain to see if it is rated as blockable or unblockable.

Blockable drains require at least 2 drains.

You never put drains where people would likely sit or otherwise make contact with the drain due to the likelihood of entrapment or other injury.


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Flowcode

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The footwell of most spas does not have enough space to get the 3' edge-to-edge (in California) clearance required for split main drains. Having them in different planes, one floor one wall, allows the system to meet code requirements.
 
1poolman1 said:
The footwell of most spas does not have enough space to get the 3' edge-to-edge (in California) clearance required for split main drains. Having them in different planes, one floor one wall, allows the system to meet code requirements.
Click to expand...
This was the logic behind doing it. 7 x 7 spa would have been tight. The only thing I didn’t like was that the drains aren’t equivalent lengths so inevitably the suction will be different between them. They will be using the covers you can plaster on so hopefully that’ll mitigate any suction issues.
 
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