True 2.5" piping unicorn

mvoltin

Silver Supporter
Aug 1, 2016
56
atlanta, GA
I have a new pool (finishing up plumbing) and have been meticulous about reading codes/recommendations/best practices/etc. on GPM and plumbing requirements. Now about to finish my plumbing (equipment side) and having trouble finding right fittings that makes me wonder about everything I have read so far - it seems really difficult to build truly 2.5" plumbing. Any advice will be appreciated:

About the pool:
I have relatively small 11,000 pool/spa combo that requires 20 to 90GPM (I have 9 waterway jets, each 10GPM) and extremely short/direct feet of head. ( will have a separate post why I need up to 90GPM and how plumbing is done - I did lots of research and it will be too much to go in this post) My plumbing is set up with 2.5" pipes.

About the standards:
Based on what I have read, 2" piping only supports around 80GPM (or 63GPM on suction and 84GPM on return side). Numbers for 1.5" are around 35GPM suction and 50GPM return. So, if the max flow requirements are above 70GPM, one should use 2.5".

Issues to achieve true 2.5" plumbing:

  • Pump: 1.5HP Pentair VS Superflow seems to perfectly fit the bill (20GPM most of the time with occasional 90GPM). Yet, the inlet and outlet on the pump are 1.5". I had previously posted about this but, frankly, responses were not quite clear. So, unless there is a good explanation, I am being forced to put 1.5" 'bottleneck' in my 2.5" piping system and cannot find a reasonable workaround unless I go with 3hp pump (which I definitely don't need).
  • Salt chlorine generators - all of them, (up to 40,000 gallon versions) have up to 2" plumbing (with further restrictions inside the box). I couldn't find residential chlorine generator with 2.5" piping.
  • Same issue with inline chlorine feeder (and they are very restricted inside, way beyond 2"). Even off-line chlorine feeders come with clamp that work on pipes up to 2"

Is it really possible to build pool with true 2.5" plumbing?
If pool has 70GPM+ requirement (max), ideally, one should use 2.5" plumbing. I can imagine many 30-40k gallon pools with extra features fall in this category. I see only three potential scenarios and any advice will be appreciated:
  • the 64GPM for 2" is arbitrary and there is lots of "cushion" for higher flows. People just stick with 2" plumbing; or they just put bunch of 2inch "bottlenecks" in their 2.5inch systems.
  • There are 2.5" fittings for salt chlorine generators and chlorine feeders through specialty stores that I cannot find (but manufacturers such as hayward would list them, right?)
  • People extensively use pressure-sensitive bypass valves that enable to direct subset of flow through restrictive salt chlorinators (that still doesn't explain what they do with pumps that are rated at 100GPM but have 1.5" inlet and outlet). Also, this set up would complicate the system and increase the overall feet of head - just doesn't seem ideal.
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mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,769
Pleasanton, CA
Smaller pipe has higher velocity and higher head loss but that is it. There are recommendations for velocity limits but those are just recommendations and not absolute limits. So having 1.5" pipe carrying high velocity water for short distances is really not an issue. You just don't want a lot of small pipe or have it close to suction ports as that can increase risk of entrapment.

Finding 2.5" plumbing is difficult as the home stores don't usually carry it. However, irrigation warehouses usually do carry it. Also, you can find it online.
 

mvoltin

Silver Supporter
Aug 1, 2016
56
atlanta, GA
Smaller pipe has higher velocity and higher head loss but that is it. There are recommendations for velocity limits but those are just recommendations and not absolute limits. So having 1.5" pipe carrying high velocity water for short distances is really not an issue. You just don't want a lot of small pipe or have it close to suction ports as that can increase risk of entrapment.

Finding 2.5" plumbing is difficult as the home stores don't usually carry it. However, irrigation warehouses usually do carry it. Also, you can find it online.
thank you. Yes, i was able to get all the necessary plumbing at 2.5”. I just cannot find the salt chlorine generator with 2.5” and pump that has even 2” intake without going to 3hp. It gives me heartburn to get a pump that can go 100gpm but has 1.5” inlet and outlet. I guess there is no better option...
 

mvoltin

Silver Supporter
Aug 1, 2016
56
atlanta, GA
The bushings for transitioning from 2.5" to anything else has insignifant impact to the plumbing. it won't be an issue.
Hi, I guess this is exactly what I don't understand: Here is the description of the recommended piping and related flow rates. And here is the hayward document that recommends 6FPS suction side and 8FPS return side (page 2). These numbers are consistent with what I found on number of other websites.

Here is the calculator based on the diameter and flow rates. For example, if the flow is 100GPM, velocity would be 6.5fps in 2.5" pipe which is fine. But when it enters the pump's 1.5 inlet, the velocity will be 18+fps inside the two points (between the inlet and outlet). Through the salt chlorine generator (2") the velocity is 10+fps throughout the generator and flow sensor (total distance of 2 plus feet minimum). The recommended flow rate within these sections will be invariably exceeded.

I just don't understand why this would be a minimal impact - i am just trying to reconcile all these recommendations. There has to be reason, otherwise, pool companies would make 2.5" chlorinator and put 2.5" inlet/outlets on their pumps....

This is how I imagine this in an oversimplified way: if a water dam is able to release 100,000 gallons per second and we put 1.5" restriction over tiny section of the dam opening, the flow is going to be impacted. Pressure washer flow, even with all the pressure behind it, is much lower than garden hose flow because of the restriction at the very end over tiny distance...
 

JamesW

TFP Expert
Mar 2, 2011
21,114
The inlet can take a 1.5" pipe into the union or a 2" coupling to the outside of the union.

So, it's 2" and not 1.5" if you use a 2" coupling to the outside. Or, you can use a 2" x 2.5" bushing to the outside of the union fitting and then a 2.5" coupling to the bushing.

It's only 1.5" if you use 1.5" pipe.

Technically, you're correct that the inlet and outlet are not compliant with best practices.

The pumps were designed decades ago when good hydraulic design was not really well understood.

Typical systems were poorly designed and excessively restrictive.

For the most part, builders just installed an oversized pump and called it good. They weren't paying for the electricity, so they didn't particularly care the energy costs.

If you use 2" pvc, the impact will be minimal.

2" pvc at 90 gpm is 8.8 ft/sec and there is about 12.4 feet of head loss per 100 feet of straight pipe or about 0.062 feet of head loss for a 6" length of straight pipe. So, minimal impact.

For 2.5" pvc, the velocity is 6.2 ft/sec and there is about 5.2 feet of head loss per 100 feet of straight pipe or about 0.026 feet of head loss for a 6" section.

The actual inside diameter of pvc pipe is:
1.5" = 1.59"
2" = 2.047"
2.5" = 2.445"

See the chart below for head loss figures or use the calculator below.

www.engineeringtoolbox.com/amp/pvc-pipes-friction-loss-d_802.html

 
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JamesW

TFP Expert
Mar 2, 2011
21,114
https://aquamagazine.com/service/how-to-read-pump-system-curves.html





See the above for an explanation of system curves and pump curves.

In my opinion, pumps should be limited to about 2,750 rpm.

This would allow for a bigger impeller and would work better for medium head applications.

The system should be designed to avoid excessive head loss.

Heaters should use automatic valves that open only when the heater is on.
 

mvoltin

Silver Supporter
Aug 1, 2016
56
atlanta, GA
The inlet can take a 1.5" pipe into the union or a 2" coupling to the outside of the union.

So, it's 2" and not 1.5" if you use a 2" coupling to the outside. Or, you can use a 2" x 2.5" bushing to the outside of the union fitting and then a 2.5" coupling to the bushing.

It's only 1.5" if you use 1.5" pipe.

Technically, you're correct that the inlet and outlet are not compliant with best practices.

The pumps were designed decades ago when good hydraulic design was not really well understood.

Typical systems were poorly designed and excessively restrictive.

For the most part, builders just installed an oversized pump and called it good. They weren't paying for the electricity, so they didn't particularly care the energy costs.

If you use 2" pvc, the impact will be minimal.

2" pvc at 90 gpm is 8.8 ft/sec and there is about 12.4 feet of head loss per 100 feet of straight pipe or about 0.062 feet of head loss for a 6" length of straight pipe. So, minimal impact.

For 2.5" pvc, the velocity is 6.2 ft/sec and there is about 5.2 feet of head loss per 100 feet of straight pipe or about 0.026 feet of head loss for a 6" section.

The actual inside diameter of pvc pipe is:
1.5" = 1.59"
2" = 2.047"
2.5" = 2.445"

See the chart below for head loss figures or use the calculator below.

www.engineeringtoolbox.com/amp/pvc-pipes-friction-loss-d_802.html

Thank you, James.
this helps. Just to clarify (I also spoke to Pentair about this), the actual opening size (actual inlet and outlet size) is 1.5" on this pump. So, even if you use 2", it goes down to 1.5" at the inlet right after the union.
 

JamesW

TFP Expert
Mar 2, 2011
21,114
Just to clarify (I also spoke to Pentair about this), the actual opening size (actual inlet and outlet size) is 1.5" on this pump.
The inside diameter of the union is 1.900", which is the outer diameter of 1.5" pvc pipe.

At 90 gpm, the velocity is 10.2 ft/sec and the head loss for 6" of pipe is 0.10 feet of head, which is not a significant amount.
 
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JamesW

TFP Expert
Mar 2, 2011
21,114
You should get the Intelliflo pump and the Intellicenter to control everything.

The Superflo might not give you the jet action you want and it's not easily controllable.

For a pool/spa combination with heat and salt, you really need automation to make it all work correctly.
 
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mvoltin

Silver Supporter
Aug 1, 2016
56
atlanta, GA
You should get the Intelliflo pump and the Intellicenter to control everything.

The Superflo might not give you the jet action you want and it's not easily controllable.

For a pool/spa combination with heat and salt, you really need automation to make it all work correctly.
Thank you, James. I will explore further these options - depending on the budget. I am not sure how much automation I will need since I will rarely operate hot-tub and pool simultaneously:
My set up is very unusual (will have another post about it - whether it works or not). I have limited space under deck and hot-tub is simply an extension of the pool (one space- one level). Most of the year pool/HT is heated as one and used as one open space (it's basically a heated swimming pool with some seating area and jets on one end). Then, in the coldest months, I plan to cover pool portion and put divider between hot-tub and pool and switch circulation just to hot-tub area (and crank the temperature up).
 

mvoltin

Silver Supporter
Aug 1, 2016
56
atlanta, GA
The inside diameter of the union is 1.900", which is the outer diameter of 1.5" pvc pipe.

At 90 gpm, the velocity is 10.2 ft/sec and the head loss for 6" of pipe is 0.10 feet of head, which is not a significant amount.
Hi James,
This doesn't change the big picture discussed on this thread but just FYI: I received the pump yesterday and the actual measurement of the inlet/outlet on Superflo is 1.63" that is roughly 1 5/8".
 

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JamesW

TFP Expert
Mar 2, 2011
21,114
I received the pump yesterday and the actual measurement of the inlet/outlet on Superflo is 1.63" that is roughly 1 5/8".
Ok, thanks for the update.

I was thinking about the inside diameter of the union that comes with the pump.

In any case, your point is valid that the diameter is undersized for the flow that's possible for the pump.

The pumps were mostly designed decades ago before they understood the importance of water velocity.

Most variable speed pumps are just old single speed designs that have been refitted with variable speed motors.

It's time for a pump redesign for the modern world.
 
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