Piping / flow questions

[gtapoolguy]

Getting a 20K pool installed. 36x18 (depths are 3.5 to 7 ft)

Have some questions on piping and flow:

Current proposed setup with Hayward EcoStar pump:

Input:
- 1 skimmer, 2" return pipe (no main drains)

Output (2" pipe out of pump, split to returns and sheer descent):
- 4 returns (1.5" pipes)
- 3x3ft = total 9ft sheer descent (one 2" pipe feeding all 3, split at the end into 3x1.5")
- Will have a valve to switch between returns or sheer descent, dont plan on running both at the same time.

Are the piping widths sufficient for the required flow?
Should I be upsizing any of the pipes (in particular should the skimmer line be wider than the output?)
Logically i'm having a tough time understanding how a 2" input pipe can feed all the outputs without some serious pressure differences.

What would you change in this scenario for sizing? Also just the sheer descent sizing indicates I likely need around 108 gpm though the pump manual recomments max flow of 80 gpm with a 2" pipe.

Help is much appreciated, thanks!

 

[JasonLion]

All of that seems very reasonable ignoring the sheer decent. However, 108 GPM is very unlikely with that system. It is not a good idea to try for flow rates that high with a single skimmer and no main drain. Are you sure the sheer decent really needs 108 GPM? If so, you will want at least another skimmer with it's own 2" pipe, a two speed or variable speed pump, and 3" piping to the sheer decent.

 

[gtapoolguy]

All of that seems very reasonable ignoring the sheer decent. However, 108 GPM is very unlikely with that system. It is not a good idea to try for flow rates that high with a single skimmer and no main drain. Are you sure the sheer decent really needs 108 GPM? If so, you will want at least another skimmer with it's own 2" pipe, a two speed or variable speed pump, and 3" piping to the sheer decent.

Thanks for the quick response. Based on some of the specs I've seen its roughly 1gpm per inch of sheer descent, hence the 108 number.

Now I'm thinking of just switching to a single 6ft sheer descent (72 gpm). Would the rest of the plumbing be sufficient with that or should I still look to increase pipe sizes? My thought was to just use either the returns or the sheer descent at any given time (but not both) hence no dedicated skimmer for the descent.

 

[JasonLion]

72 GPM is plausible with that plumbing assuming the pipe runs are not extremely long. The longer the pipe runs, the more advantage you get from using larger pipes for the skimmer and sheer decent.

A two speed or variable speed pump would be good here as you really only need 72 GPM when running the sheer decent, and are better off with a much lower flow rate when just filtering.

 

[gtapoolguy]

the runs are approx 80' long.

would it be beneficial to upgrade the sheer descent and skimmer pipes to 2.5 or even 3" pipes? is there any downside to doing that (assuming all return pipes stay at 1.5")?

using ecostar variable speed pump, so should be able to dial the power as needed

 

[JasonLion]

With 80' foot runs, going to 2 1/2" pipe seems worth it. 3" is of course better, but not that much better and more expensive, which you need to balance out for yourself. The only downside to larger pipes is the expense and the slightly higher difficulty of finding fittings. On the other hand, the advantages of going larger get smaller as you get larger. 2" to 2.5" is a fairly large improvement, going from 2.5" to 3" a much smaller improvement, though still noticeable. And advantages continue to get smaller as you go up from there.

 

[bmoreswim]

On a pool that size, it seems that 2 skimmers would also be a good idea. That's asking a lot of the surface water movement to get that much SF of surface area all directed to one skimmer reasonably efficiently. We have two on a similar footprint and it works well for us. That's just a gut feeling though, others may say one is all you need for sure. This comment is not intended to address flow requirements for the sheer descents, just flotsam and jetsam removal.

 

[gtapoolguy]

thanks bmoreswim, i was just coming over to ask that same question...

jasonlion, will a 2nd skimmer alleviate some of the flow concerns (but keeping all piping at 2")? so now 2x2" pipes coming from skimmer, 4x1.5" returns and 1x2" pipe for sheer 3x3ft sheers?

 

[JasonLion]

A second skimmer, or a main drain, is certainly a good idea. Having two skimmers has become very common these days, as it is just better in a number of ways. With the flow rate concerns it is even more valuable. Two skimmers each with a 2" pipe to the main pad would be fine. I'd still go with 2 1/2" to the sheer descent.