Flow rate to low on low speed

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bk406

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Dec 3, 2009
2,684
Central Massachusetts
Ok guys, a little help with my system. Was hoping Mark could chime in, but anybody who has ideas feel free.
So a little background first. I have a 14000 gallon IG plumbed with:

1.5 inch pipe on a skimmer run back to the pump
1.5 inch pipe on a side wall suction run back to the pump. Both suctions tied together at a jandy valve before going into the pump.

3, 1.5 inch returns

Originally, I had a 3/4 HP Hayward super pump. It died last season so I decided to get a 2 speed. Bought a pentair superflo 1 HP. The idea was to run it on low to save on power. Well, unfortunately, there's not enough flow for my IC-40. It needs 20 gpm, but practically it may need 22-23. Bottom line I have to run it on hi to make chlorine. Using Marks spreadsheets and calculations, I have somewhere around 55 feet of total head based on a 17 psi pressure with the pump on high on a clean sand filter (17*3.21). Need to lower the total head.

The 1.5 inch pipe I can't do anything about. However, I can do something about the size of filter I have. The builder put one in waaayyy undersized. It's a Hayward S180T. Basically 1.75 sq ft and a 32 gpm rating. I needed to upsize the filter from day one, just haven't done it.
So to get to my question, 2 really.

1) if I up size the filter, can I lower the total head to get 22-23 gpm on the system
2) what size filter would I upsize to based on a 14000 gallon pool and a 1 hp Superflo 2 speed
 
Up sizing the filter may or may not solve the problem. A couple of questions.

Distance from pool to pump
Pump height relative to water level
 
mas985 said:
Up sizing the filter may or may not solve the problem. A couple of questions.

Distance from pool to pump
Pump height relative to water level
Click to expand...

Hi Mark,

Ok I went out and stepped everything off. It's not exact, but it'll be close.
1) far return ~50 feet
2) 1st stair return ~20 feet
3) 2nd stair return ~ 21 feet

4) skimmer ~ 40 feet
5) wall suction ~ 38 feet

Pump is basically top of pool. So the skimmer pipe is maybe a foot lower, and the suction about 18 inches.
All 5 runs are on separate 1.5 inch pipes. The only fittings below ground are 90's on the returns and the suction. It's plumbed with poly, so there are no fittings otherwise. The 2 suction lines terminate on a single Jandy valve. The 3 returns terminate on a 3 way manifold (no valves).
Probably no hope to lower the head. Now I wish I just have gone back to the single speed 3/4 hp pump.
 
So I get 48 GPM at 50' of head for high speed and 23 GPM @ 13' of head on low speed so the SWG should work. However, the head loss on the return side is quite high but it could be several things. Can you take a picture of the pad equipment? Since the three returns are on separate runs, it is probably something on the pad and it could be the filter.

Also, what size are the return eyeballs?

Does the SWG have a bypass built it and can you tell if the check valve is closed on low speed?
 
My back of the napkin calculations tod me about 16-17 feet of head on low. That's based on 5 psi on the gauge on low speed. I think I'm right below the limit.
It's dark at this point so I can't take Picts until tomorrow at some point.
Couple things that might help besides a bigger filter.

First, I have 2 heaters, a heat pump and a gas heater. I can bypass the gas heater and only run through the heat pump. But, when I do that, I'm still below the flow rate for the generator.

Second, the generator is plumbed just after a 90 that comes out of the heater. There's a 90, maybe 10 inches of pvc then the generator. Coming out of the generator, there's no straight pipe at all. They have a 90 right out of the unit then out to the pool. So there's no straight run out.
I was hoping if I upsized the filter, and repositioned the generator with at least 12 inches of straight pipe on either end, I might increase the flow rate above the threshold.
The generator doesn't have a bypass.
Not sure on the eyeballs, maybe 3/4" hole
 
Having a straight run after the generator shouldn't make any difference. But heaters have a lot of head loss and two is twice the amount so if you can bypass one, then that should help.

Do you also have check valves in the plumbing? On low speed, you should have only about 3 PSI of pressure. Having 5 means that there is some extra head loss on speed that isn't there on high speed and spring loaded check valves do that which is why I wanted to see the pad equipment. Do you have any check valves that look like this:

BadCheckValve.jpg

These are the worst check valves for head loss.
 
I can bypass the gas heater and only run thru the heat pump. But even bypassing one heater, I still get low flow.

I have one check valve. It's positioned so water won't back up into the gas heater when I have it bypassed. The check valve is a jandy withe the clear top.
 
After you open, I would try recirculate first just to see if that would make a difference before changing out the filter.
 

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Your probably right, but I still think the filter is undersized. I'm just really disappointed in the 2 speed. My rates aren't high enough to justify a VS so I thought a 2 speed would work nicely. Knowing what I know now, I would have specified 2 inch plumbing instead of 1.5 " but too late now.
 
I don't think 2" would help much except maybe on the pad. You have multiple runs for both suction and return so pipe size is not as important. There is clearly something on the pad that is causing the issue and it is probably the filter but I wouldn't assume that it is either.
 
I can definatley re-plumb the pad and make it a bit better I think. It's a mix of 2" and 1.5". Maybe if I change it all to 2 inch, move the generator to better position, optimize the bypass a bit better and increase the filter size I can squeeze out 2-3 more gpm.
What size sand filter would you go to? 24"?
 
Just curious are you able to easily bypass the multivalve? Before you invest in a new sand filter if your getting drop because of the multi port valve, you could go with a cartridge filter and gain the flow you need in low.
 
Like Mark said, I can put the mutiport on recirculate and bypass the filter to see if the small filter is the issue. If it is the filter, a larger might help to decrease the total head. I like the features a multiport and sand filter give me, so a cartridge filter is not really an option for me.
 
If you do change out your filter, then make sure you get a 2" multi-port valve. They half the head loss of a 1.5" valve which has a lot of head loss.
 
For areas where the pool is closed for the winter, a cartridge filter can be a PITA during spring clean up.
 
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