Effect of increasing size of filter pad outlet side hose only?

[Websherpa]

My question is, can I increase flow back to a pool water feature by increasing pipe size from 1.5 to 2" on the pool pad outlet side only and not changing anything else?

Our pool was originally plumbed all 1.5" with a 18" Sheer Descent, stair jets, return jets and with a Pentair Superflo VST it all runs fine, if we want a little more output for the sheer descent towards the end of the season, we can crank the RPM and just close back the pool return jets a little to force more flow through the water feature return pipe. The run is about 60+ feet filter pad to water feature and 1.5' above water level, with very minor slope up to pool (no check valve was required). I physically measured the flow (bucket and watch method) from the 18" Sheer Descent at full RPM (3450) and only waterfall valves open. It was about 33 gals per minute, but it's also the end of the season and the DE filter is starting to restrict the flow by at least 20%.

We have no reliable pool company that I can get a straight answer from at the moment.

We are replacing the patio and coping above the sheer descent and were hoping to install a 3 or 4' sheer descent in place of the 18" one and continue to use the main filter pad pump. So I thought about upgrading the output side of the pool plumbing to a 2" pipe run. Before I commit to an installer, I am trying to determine if this alone would this help increase the flow in the pipe to more adequately supply a 3-4' Sheer Descent with a small projection?
My read on the Sheer Descent specs seem to indicate it would work up to about a 3' sheer descent, but I'd like to install a 4' one and be sure it would work, but don't want to commit only to learn later it isn't enough flow.
Moving to a 3hp Intelliflow is a possible future option, but the Superflo VST still has some good life in it.

The cost to install a separate run, cut new dual inlets and separate pump goes above our available budget.

 

[ajw22]

Do you have an MPV on your DE filter with a RECIRCULATE setting?

Do you have a Heater Bypass - Further Reading

Try bypassing your filter and heater and seeing what GPM you get.

I doubt your 1.5" return runs are the limiting factor in your flow. It is only once you get above 50 GPM on returns that changing from 1.5" to 2" can be a benefit.

You want to keep the water velocity below 6 ft/sec on the suction and below 8 ft/sec on the pressure side of the pump.

Pipe Size	6 ft/sec	8 ft/sec
1.5"	38 GPM	51 GPM
2"	63 GPM	84 GPM
2.5	90 GPM	119 GPM
3.0"	138 GPM	184 GPM
4.0"	235 GPM	312 GPM

 

[Websherpa]

Do you have an MPV on your DE filter with a RECIRCULATE setting?

Do you have a Heater Bypass - Further Reading

Try bypassing your filter and heater and seeing what GPM you get.

I doubt your 1.5" return runs are the limiting factor in your flow. It is only once you get above 50 GPM on returns that changing from 1.5" to 2" can be a benefit.

You want to keep the water velocity below 6 ft/sec on the suction and below 8 ft/sec on the pressure side of the pump.

Pipe Size	6 ft/sec	8 ft/sec
1.5"	38 GPM	51 GPM
2"	63 GPM	84 GPM
2.5	90 GPM	119 GPM
3.0"	138 GPM	184 GPM
4.0"	235 GPM	312 GPM

Thank you for this.
So increasing the return diameter isn't going to help with the outflow, just the capacity to flow faster than I need for this purpose?

The original installer cheaped out a bit on the install (which is why we're having to replace the patio).

There is no MPV on the DE filter (fun, fun, fun filtering the DE off the filters at the end of the season), no Heater Bypass (but it does seem to be a smart addition in any case).

Maybe then it's safe not to replace the pipe, but minimize the head pressure at the pad (as suggested), try it, and then upsize the pump if the desired flow isn't achieved?

The Sheer Descent manual states that a "Standard 4 foot model requires only 48 gpm to operate" (12 gallons per minute per foot with minimal head loss is the recommendation for minimal operation and water projection.
Since I'm currently getting only about 33gpm (with clogging filters) it makes me think I'm on the edge of being inadequate for 4' of waterfall.

The waterfalls require a filter in order not to become clogged themselves, but I wonder if the filter basket alone is sufficient with a MPV bypassing the cartridges?

 

[ajw22]

I would start by seeing what flow you get with a clean filter.

A clean filter with a 3HP Intelliflo pump and heater bypass will probably get you the around 45 GPM.

The pump and skimmer baskets are not a filter. Stuff gets through them.

 

[JamesW]

I physically measured the flow (bucket and watch method) from the 18" Sheer Descent at full RPM (3450) and only waterfall valves open. It was about 33 gals per minute, but it's also the end of the season and the DE filter is starting to restrict the flow by at least 20%.

33 GPM at 3,450 RPM indicates excessive head loss.

The head loss is about 72 feet, which is about 31 psi.

That is a system curve of about H = 0.0661157F^2, which is horrible.

What is the filter pressure?

A 4 foot sheer requires about 48 GPM.

The sheer might produce about 10 feet of head at 50 GPM.

Suction: 7 feet.
1.5" Pipe: 14.3 feet.
2" PVC pipe = 4.2.
Sheer: 10 feet.
Static lift = 2 feet.

7 + 14.3 + 10 + 2 = 33.3 feet with 1.5" pipe.
7 + 4.2 + 10 + 2 = 23.2 feet with 2" pipe.

Changing the pipe makes about 10.1 feet of difference in head loss but there must be a problem on the suction side or the return side with 72 feet of head loss if the 33 gpm is accurate.

72 - 33.3 = 38.7 feet of extra head loss, which is 17 psi.

If you changed to 2" pipe, the system curve and the operating point would not change very much.

H = (0.0661157 - 0.00572000 + 0.00168)F^2.

H= 0.0620757F^2.

Your pump should be able to do about 50 GPM all the way down to about 1,730 RPM.

So, you need to figure out why the system is so restricted and solve that before you are going to be able to get 50 GPM from the pump.

https://www.bestbuypoolsupply.com/media/sheerdescenttech.pdf

https://cdn.fluidrausa.com/-/media/zodiac/global/downloads/h/h0347100.pdf

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/manuals/pool-pumps/superflovs/supervs-install-english.pdf

 

[JamesW]

The heater should be about 7 feet of head loss and the filter maybe about 5 to 7 feet plus maybe 5 feet for the multiport.

Suction = 7 feet.
1.5" Pipe = 14.3 feet.
Sheer: 10 feet.
Static lift = 2 feet.
Heater = 7 feet
Filter = 7 feet.
Multiport = 5 feet.

7 + 14.3 + 10 + 2 + 7 + 7 + 5 = 52.3 feet (22.64 psi) with 1.5" pipe.

Try cleaning the filter.

Maybe you have some sort of clog on the suction or maybe a clogged impeller, pump basket, or skimmer basket.

You might need to get a vacuum gauge to check the suction pressure.

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/manuals/training/Sta-Rite%20Basic%20Training%20Manual.pdf

This is from the Jandy JXI, but it has a similar design, so the head loss should be similar.

It has a double pass heat exchanger.

 

[Websherpa]

I was measuring the flowrate using a VERY unscientific method. 5 gallon bucket, iphone stopwatch, collecting half the waterfall and multiplying by 2. The 18" waterfall itself could be the limiting factor as it most certainly wasn't handling the full flow at 3450 RPM on the Superflo VS.

The Sheer Descent is only 1ft above waterline and right on the edge of the bond beam (meaning no deck to get over).

On top of that I am surprised that the DE filters are as clogged as they are, usually they do just fine until the end of the season in October with me never needing to clean them mid-season. Maybe I over-charged them by accident. The pressure gauge on filter top is halfway between the starting pressure and the "clean me now!" line when system is fully opened and max 3450RPM.

For some reason when you don't have a pool guy everything up here in Canada for pools are WAY more expensive to get through LPS or amazon.ca.

However I'm going to install an inline flow meter now to get ahead of the game (should have originally) and put a real pressure gauge on the filter as well as investigate further.
(If the advantage of a 2" return line to the waterfall isn't worth it I won't but I was originally more curious to know the true effect, especially if there are no changes on the intake side, since it can be more easily done with the patio removed.)

 

[Websherpa]

I meant to say that the standard pressure gauge at the top of the DE Filter @ 3450rpm (top speed), is (at this time of year where the filter is clogged and we only have about 30 days of open left):

All valves OPEN (stair jets, return jets, sheer descent 18" ): 14psi (this was 9psi at the OPENING of the pool, there is barely enough projection to make the feature work, but at beginning of season, at full speed, it is fine)

Sheer Descent CLOSED (stair & return jets OPEN): 15psi

Only Sheer Descent OPEN (stair and return jets CLOSED): 20psi
The Sheer Descent is the longest run of 1.5" pipe from the pump pad, at least 60'
18" Sheer Descent only, I would need to turn the RPM down significantly, generally through the season if I turn off the stair jets, I can run Sheer Descent (with perfect projection) and return jets fully open at nominal operating RPM 2250 - 2400

So at this stage I really just need to determine if I can adequately run a 4' Sheer Descent without changing out the piping to 2". I likely will pull the pump apart and service it (I have all the required seals as this pump may have a small rock in it - sounds like it anyway, plus I have an older backup Superflo VS that works as well as this one).

I will put in a heater bypass next season though and maybe a MPV for the Quad 100 as it's a b&tch to filter out the DE at end of season (I use a filter bag for most of it, bury the rest - we're not supposed to dump DE into the sewers). The reason there is no MPV is the original installer oversized the DE filter so it could run all season without backwashing it, although I think he anticipated dumping the DE into the sewers, which I won't.

 

[JamesW]

We need to know the flow, suction pressure and return pressure at 2,200 RPM, 3,000 RPM and 3,450 RPM.

 

[Websherpa]

Is there a FAQ for making those measurements and related equip? Thank you!

 

[JamesW]

You can put a vacuum gauge in the pump front drain plug, but be careful because the hole can crack if you screw it in too tight or if you use too much Teflon tape.

There are several types of flow meter that you can get.

 

[Websherpa]

Thank you, I am learning so much! (I'm a techy, gotta get it perfect kind of guy so research everything to death, lol)
So just to confirm, suction pressure at the front pump drain, but where are the optimum (or required) locations for the a) Flo meter (I have one en-route already), and b) return pressure (should I assume it's the pressure at the filter top, or is it elsewhere?).

Thank you!!

 

[JamesW]

where are the optimum (or required) locations for the a) Flo meter (I have one en-route already), and b) return pressure (should I assume it's the pressure at the filter top, or is it elsewhere?).

The flow meter should be after the filter so that debris and grit like sand do not clog the meter and make it inaccurate.

The return pressure is the filter pressure.

Make sure that the gauge is working correctly.

Maybe replace it to be sure.