New Owner Build Plumbing Questions

[JamesW]

So, for all pools with IntelliFlo pumps, you recommend 3" plumbing?

In any case, the skimmer's design flow rate won't support the Intelliflo at full speed.

Also, the flow is distributed over 2 skimmers and the main drain.

The Intelliflo can be password protected to keep unauthorized persons from reprogramming it or you can get the I1 if it's a big concern.

I seriously doubt that an inspector would require 3" plumbing on this pool.

If you have 140 gpm coming out of 1/2" eyeballs, that seems like the velocity would be dangerous unless you have a bunch of eyeballs but then they wouldn't provide sufficient head loss to matter.

1 eyeball = 230 ft/sec. (I'm pretty sure that's what they use on water jets that cut steel lol).
2 eyeballs = 115 ft/sec.
4 eyeballs = 57 ft/sec exit velocity.

 

[mas985]

So, for all pools with IntelliFlo pumps, you recommend 3" plumbing?

Not in all situations. In this case, because of the equipment and plumbing layout results in such a high flow rate operating point AND they needed/wanted to meet the NSF 50 standard.

There are situations where 2.5" would be sufficient. For example, if the runs were longer, the return side used 2", a filter with a backwash valve was used and a heater was added. It just depends on the configuration and resulting plumbing curve. Also, if you don't care about the standard and it is not enforced, then you can do whatever you want. But I would never use 2" on this pump for the suction.

Also, the flow is distributed over 2 skimmers and the main drain.

Each suction line is plumbed to the pad with presumably a valve so you have to account for the scenario where each suction line is isolated. It doesn't matter if the normal operation is with both lines open. As long as the possibility exists for shutting off one line or the other, you must account for both scenarios when testing against the standard.

 

[JamesW]

Since the pump can exceed the skimmer's design flow rate, one could argue that the pump should not be allowed.

In any case, you're not going to get 140 gm on a skimmer.

I think that a 2.5" from the main drains and separate 2" lines from the skimmers going into 2.5" Ts at the pad and then 2.5" into the pump is a good solution and would pass inspection.

Ultimately, it's up to the local codes to dictate what's required and for the inspector to pass the installation.

9.8.3 A skimmer’s maximum flow rating (GPM, LPM) shall be specified based on the nominal pipe size
intended to plumb the suction line (and/or equalizer line). The maximum velocity for any nominal pipe size
shall not exceed 6 FPS (1.83 MPS).

So, the flow can't exceed 6 ft/sec based on the plumbing size of the skimmer. Residential skimmers are designed to take 2" pvc and that sets the maximum flow rate and upsizing the plumbing would not allow for any increase in flow rates.

Skimmers are usually limited to about 55 to 75 gpm. To meet the standard, those limits must not be exceeded. Designing the plumbung to go above those limits is not going to make any difference.

 

[mas985]

In any case, you're not going to get 140 gm on a skimmer.

Why not? Those are flow rate recommendations. And much like pipe, it is possible to exceed the recommendations. There is nothing that will fundamentally limit the flow rate. Granted it could possibly damage the skimmer.

So, the flow can't exceed 6 ft/sec based on the plumbing size of the skimmer. Residential skimmers are designed to take 2" pvc and that sets the maximum flow rate and upsizing the plumbing would not allow for any increase in flow rates.

Read the requirement again. It states:

9.8.3 A skimmer’s maximum flow rating (GPM, LPM) shall be specified based on the nominal pipe size
intended to plumb the suction line (and/or equalizer line). The maximum velocity for any nominal pipe size
shall not exceed 6 FPS (1.83 MPS).

That means the pipe connected to the skimmer.

 

[JamesW]

The skimmers are nsf certified up to about 55 to 75 gpm. Going above that is not compliant with nsf certification.

Also, at some point you're going to start exceeding the capacity of the skimmer to allow in water without sucking in air.

If the hole at the bottom of the skimmer is 2", that's the limiting factor.

Unless you get skimmers that take 3" pvc and are rated at 140 gpm, 3" pvc is not going to help.

In any case, I don't think that you're suggesting that the skimmer ever be operated above about 60 gpm, so why design for it?

Even if you tried to go to 140 gpm, how would 3" pipe make it safer? You still have the same velocity at the bottom skimmer hole.

 

[mas985]

The skimmers are nsf certified up to about 55 to 75 gpm.

Yes, that is a certification. It just means it was tested up to those flow rates. It could mean they would not pass inspection but the standard itself makes no mention of that so I am not sure it is used in compliance.

Look, I am not saying these standards are perfect. The OP wanted the pool to be compliant. I am just passing on the information on how to do that. If the building codes don't require it, the OP can ignore if it they choose.

But looking back at the original post, it looks like they are following ANSI/APSP-7 standards and not NSF 50 standards. They are very similar but the ANSI/APSP-7 relaxes the flow rate requirement for residential pools (and tightens other requirements). Here is an older version:

https://www.wvdhhr.org/phs/pools/Virginia%20Graeme%20Baker%20Act/ANSI-APSP-7%202006%20suction%20entrapment%20PDF%20with%20covers.pdf

So that means you still would need to use 3" for the cross TEE in the main drain but all other suction pipe could be 2.5" and still meet ANSI/APSP-7. But again, only if you use 1/2" eyeballs. As to the flow rate of the skimmer itself, it isn't mentioned specifically in this doc either.

 

[JamesW]

Ok, I guess that I don't see the point in designing for some theoretical situation that should never happen. Someone would have to intentionally close all valves except one and then reset the pump's maximum rpm and then turn it up to maximum. Even if they did how would 3" plumbing help anything?

Also, does the standard use the maximum possible flow that can theoretically be put on a line or does it use the intended flow?

And, the skimmer has to take a 2" mta or threaded nipple before going up to 3". So, it's 2" minimum pipe size even if it's only for a short distance. The minimum pipe size dictates the maximum flow rate.

 

[mas985]

Ok, I guess that I don't see the point in designing for some theoretical situation that should never happen. Someone would have to intentionally close all valves except one and then reset the pump's maximum rpm and then turn it up to maximum. Even if they did how would 3" plumbing help anything?

For the MD, I think the larger pipe would certainly help because the velocity entering the pipe (assuming it is 3") would be reduced so less likely to entrap hair. BTW, I believe the velocity requirement is only for hair entrapment so that only really matters for the main drains as it is nearly impossible to get hair trapped in a skimmer and if you did, it wouldn't hold you under water. However, they still set a maximum of 8 fps on all suction lines but again, they don't really set a velocity restriction for the skimmer or the fitting attachments to the skimmer, just the nominal pipe size.

Also, does the standard use the maximum possible flow that can theoretically be put on a line or does it use the intended flow?

They call out the "Maximum system flow rate" which to me means the maximum possible given the plumbing setup and various operating conditions. Otherwise, then would have used wording such as "typical operational flow rate". If there are stops on the valves and/or the pump is limited in RPM without possibility of change, then perhaps that is acceptable.

But what you or I think doesn't really matter. It is what is required by the inspector and that original TDH sheet, although glaringly wrong, may be enough. My only objective here was to help the OP with the original question.

Here is some more information on compliance:

http://www.floridabuilding.org/fbc/commission/FBC_1015/commission_Education_POC/646/646-0-MATERIAL.pdf

 

[JamesW]

The reference that you linked to seems to distinguish between a "Certified Secured control system" where the flow rates are set by a Registered Design Professional and an unsecured control system. A secured control system has

No access by unauthorized personnel who could make adjustments changing flow rates.
No Access:
Locked
Password protected
Valve handles locked, etc.

The pump can be password protected, so that might make a difference.

I think that the main questions are:

1) It it required by local code? I don't think so, but I don't know for sure. I would be surprised if an inspector would require 3" pvc from the skimmers. The OP is going to have to check with the local inspector on that.

2) Is the line ever going to carry more than 60 gpm? It shouldn't, but that doesn't mean that someone can't misconfigure the system to put 100% on one skimmer and turn the pump to 3450 rpm. But you can't prevent all misconfigurations. For example, someone could close all of the valves and turn the pump on high.

If the skimmer has an equalizer line, the equalizer line is the limiting factor because, if the float valve closes, all suction goes to the equalizer, which is a submerged suction outlet and normally rated at about 55 gpm.

 

[jte]

Lots of good info here, I really appreciate it. While I completely understand that a 2” port on the skimmer and 2.5” port on the specified main drains is the limiting factor, the fact that florida building code addresses these velocities verbatim with what my engineered drawings show makes me hesitant to change anything. I’m no fluid dynamics expert, but I believe I will end up with a variety of velocities throughout the lengths of pipe. It’s stupid to connect a 4” Tee to the 2.5” ports on the double main drains, but the inspector can’t tell me I’m wrong in that case. And as you’ve pointed out, I can increase my velocities if needed by going to a 1/2” eyeball. As a commercial builder, the inconsistency and lack of published standards in the pool industry is frustrating. There’s a lot of “doing what’s always been done” that I don’t trust, especially with the development of more efficient equipment. From my understanding, ten years ago it would have been unheard of to put a 3hp pump on a 17k gallon pool and now it’s the norm. So pool designs must catch up to the technology. Thank you all for the input. I’ll start a thread when I start construction.

 

[mas985]

I would add one last word of caution if you decide not to use 1/2" eyeballs. If you operate a pump close to or beyond the pump's run out, you can and probably will damage the pump. The impeller experiences very high lateral and axial loads when operating in that region. Also, cavitation is almost certain. Even operating at lower RPM may not mitigate all of these risks.

Runout Definition | Pump Terms | Intro To Pumps
Some Effects of Operating Pumps Away from Best Efficiency Point - Empowering Pumps

The pump can be password protected, so that might make a difference.

But that has to be done by a certified profession so the PO would be locked out of all access which I would never stand for.

 

[JamesW]

I would think that the owner could be designated as a qualified operator if they are given written operating instructions.

Also, both skimmers can be Teed together above ground before a valve so that you can't have just 1 skimmer on.