Separate and idependent drains needed for two pumps?

GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
In my setup I will have two Pentair 3HP VSF pumps. The first pump will provide the flow for the pool and spa, and the second pump will provide the flow for all of the water features (three 18" sheer descents, three bubblers, and two deck jets).

Currently the roughed in plumbing consists of the pool main drain, spa drain, and two skimmers, all of which will be connected to the first pump to supply the first pump with water. Does the second pump need its own independent water supply source (e.g. an additional dedicated sidewall drain connected to the second pump), or can both pumps share the same roughed in supply source (i.e. pool main drain, spa drain, and two skimmers). If it matters, pool main drain is a 2.5" home run line, skimmers each have their own 2" home run line, and spa drain is a 2" home run line. Spa and pool are integrated.
 

Jimrahbe

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Jul 7, 2014
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G,

Each pump must have its own water source.. Assuming you plan to run both pumps at the same time..

Thanks,

Jim R.
 
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ajw22

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Does the second pump need its own independent water supply source (e.g. an additional dedicated sidewall drain connected to the second pump),

Yes

or can both pumps share the same roughed in supply source (i.e. pool main drain, spa drain, and two skimmers).

No
 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
G,

Each pump must have its own water source.. Assuming you plan to run both pumps at the same time..

Thanks,

Jim R.
Can you help me to understand why this is the case? If I am going to insist that the PB add an additional drain at this point, I am going to need to be able to explain the reasoning behind why it is necessary.
 

JamesW

TFP Expert
Mar 2, 2011
23,996
You need to review the installation instructions for your main drains.

The total flow needs to be less than the rated flow of the single unblockable drain or the combined flow of multiple drains.

Some unblockable drains have multiple ports that can be used to supply water to two different pumps if the instructions allow.

For example, the following drain is listed as suitable to supply two pumps as long as the maximum flow rate is not exceeded.


In the above case, each pump would have its own line to the main drain.

If you have two main drains, I don't think that you can T two separate lines together to feed two separate pumps even if you do it right by the drains.

The drains would need to have two ports and each pump would get its own line that connects to both main drains on separate ports and only if the installation manual allows for multiple pumps to be connected.

I would have separate sets of main drains for each pump.

Call the building inspector to see what your local code is.
 
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JamesW

TFP Expert
Mar 2, 2011
23,996
If there is only one line from the main drains to the pad, you can only connect it to one pump.

I would just connect the feature pump to the main drains and not connect to the main pump.
 
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ajw22

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Jimrahbe, ajw22, or anyone else, can you help me understand why each pump must have its own water source? With that information, I can go to the PB and explain why an additional drain needs to be added even though the gunite has already been poured.


You can't guarantee that both pumps will get sufficient flow from one shared suction source. And you can't guarantee that the water flow will be equally balanced between the two pumps. One pump could be flowing water and the other could be running dry. Pump performance is based on having a dedicated suction intake and not sharing it with another pump fighting the suction.
 
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JamesW

TFP Expert
Mar 2, 2011
23,996
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”...........234.............313 gpm

Based on the 2.5" line from the main drains, the maximum flow should not exceed 90 gpm.

The problem with connecting two pumps to a single suction line is that they will be fighting each other for water and neither pump would work right.
 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
If there is only one line from the main drains to the pad, you can only connect it to one pump.

I would just connect the feature pump to the main drains and not connect to the main pump.
There are two main drain ports in the bottom of the pool, but they tee into a single 2.5" line that runs back to the equipment pad. Each of the two skimmers has its own dedicated 2" line that runs back to the equipment pad. There are 6 returns, that all branch off of a single 2" line that runs from the equipment pad.

It appears my options are to either:

1. Have the main pool pump pull from the two skimmers only, and have the features pump pull from the main drain only; or

2. Try to convince the PB to install a dedicated wall drain that the features pump (and only the features pump) would pull from (even though gunite is finished and deck is scheduled to be poured within a couple days). This would also then allow the main pool pump to pull from the two skimmers AND the main drain.

One concern I have with option 1 is that if my main pool pump is pulling from the two skimmers only (and not also the main drain that's in the bottom of the 8' deep end), then when the heater is on I may not get sufficient mixing of the heated water between the surface layers of the water and the deeper layers of the water. Other concern is that with the main pool pump pulling only from the two skimmers, is it possible that I might not be providing enough flow to the main pool pump? On the other hand, the problem with option 2 is that it could be a battle to get the PB to add a dedicated wall drain at this stage and at best it would delay construction, so I wouldn't want to do it if there is no significant reason to do so.

JamesW, ajw22, Jimrahbe, jimmythegreek, or others, which option would you recommend?

 

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JamesW

TFP Expert
Mar 2, 2011
23,996
Based on the 2.5" line from the main drains, the maximum flow should not exceed 90 gpm.

Hopefully, the features don't need more than 90 gpm.
 
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ajw22

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Jul 21, 2013
24,782
Northern NJ
Pool Size
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What is the status of your build?

Your gunite been shot?

Post pics of your current hole in the ground.
 

GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
Based on the 2.5" line from the main drains, the maximum flow should not exceed 90 gpm.

Hopefully, the features don't need more than 90 gpm.

Thank you for your reply JamesW. All of the information you have given so far is invaluable.

What happens if my features do need more than 90 GPM? How bad would that be?

I don't have the specifications for the water features (since I don't yet know what models the PB is planning to use), but I will have three bubblers, three 1.5' sheer descents, and two deck jets. Based on this "Further Reading" article Water Features - Further Reading, "sheers require about 12 gpm per linear foot" (so that's 54 GPM for all three sheers combined), and "deck jets don't require very much flow." As to the bubblers, I have searched and the best info I have found indicates that many bubbles are 30 GPM each, so for my three bubblers that would be 90 GPM combined. That means my bubblers and sheers combined could need around 144 GPM, and that's not even including whatever the deck jets need! So regardless of the exact specifications of the particular features my PB installs, it appears quite likely that I will need more than 90 GPM. What are your recommendations?

What is the status of your build?

Your gunite been shot?

Post pics of your current hole in the ground.

Gunite has been shot. Long plumbing has been done. Deck is scheduled to be poured within the next couple days. See attached picture of current progress.

View attachment 317398Current.jpg
 

JamesW

TFP Expert
Mar 2, 2011
23,996
What happens if my features do need more than 90 GPM? How bad would that be?
Going beyond 90 gpm will likely violate the building code. So, it is a bad design if you need more than 90 gpm.

From a physics point of view, you can exceed 90 gpm up to the point where the pump begins to cavitate, which depends on the length of the pipe and the height of the pump above the surface of the water.
 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
Is that the only spa suction?

If yes, that might be a problem if you need high flow for spa jets.

Yes. There are two drain ports in the spa that Tee into a single 2" line, that then home runs back to the equipment pad. There is no other suction in the spa. There is a air blower to the spa jets that is supplied via a separate line.
 

JamesW

TFP Expert
Mar 2, 2011
23,996
Each jet has a specified flow rate or range.

You can multiply the flow rate required per jet by the number of jets.

Hopefully, the number will not exceed 63 gpm.
 
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ajw22

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2. Try to convince the PB to install a dedicated wall drain that the features pump (and only the features pump) would pull from (even though gunite is finished and deck is scheduled to be poured within a couple days). This would also then allow the main pool pump to pull from the two skimmers AND the main drain.

I think you should insist on 2 even if it costs you a bit of money.

The PB will have to trench to the side of the pool and then core drill a hole to inset a hole for a 2.5" or 3" PVC pipe and then hydraulic cement around the pipe. Just a bit of extra work to lay a new suction line in and a VGBA suction port on the side of the pool.

Anything else is going to be a compromise that will limit you forever. Do it once the right way.

Your PB never should have recommended connecting two pumps to one suction line. Split the cost of the new line or have him agree to charge you his actual costs to install it.
 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
Status of my in-progress build is that the gunite has been shot, but this is basically it. Plaster, coping, waterline tile, etc. has not been done yet. I want to add an additional 3" suction line into the sidewall of the pool. This would presumably mean drilling a pair of 3" holes (for anti suction entrapment purposes) through the gunite shell sidewall of the pool. Is it a big deal to do this or no? Can it be done without any significant risk of compromising the gunite shell of the pool? Can it be done without significantly increasing the chances that the pool will leak? If so, what is the proper procedure? Core drill the holes and insert pipe, patch around the opening with hydraulic cement, and then plaster coat as usual? Anything else I should be aware of?
 

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