Mysterious reduction in water flow (not caused by filter)

[senex]

Hi all, I've been using the TFP methods for several years with good results.

This fall my waterflow reduced dramatically, which I assumed would be solved by cleaning the cartridges, but that didn't work, and even installing brand new Pleatco cartridges yielded no improvement.

When my filter was new a few years ago, I got 50gpm at 2200rpm. Now I get 25gpm, even with the brand new cartridges (installed today). I am perplexed about what could cause such a huge reduction. My plumbing hasn't changed and there are no visible/obvious problems. When I adjust the valves to pull or return water only from/to the pool or hot tub, there is no significant change, which I think rules out a blocked pipe.

The only thing I can't bypass is the pump, the filter, the heater, and some check valves on the return lines. I don't know how to diagnose whether the pump is misreporting gpm, or whether the heater or check valves are severely restricting flow.

I got lazy with calcium & pH control this summer, and my saturation index was probably 0.7 - 1.0 for most of the summer. Could that cause tremendous scale buildup somewhere (in the heater?) that is restricting flow? Is there any way to confirm or fix that issue? I am stuck.

FC 1.0
CC 0.0
pH 8.0
TA 110
CH 575
CYA 35

Oh, also, the heater hasn't run in several years, and is actually unable to run due to a gas line problem I never fixed.

 

[Texas Splash]

There are two things I would inspect first - the heater element and the pump impeller. Sometimes debris can get wrapped-up around or in the grooves of the impeller which might effect water pull. Based on your potential for calcium scale, the heather core is a real possibility. Too bad you don't have a bypass for that one. You'll either have to get in there to inspect or just cut it out now since it doesn't work anyways and make a bypass now.

 

[Texas Splash]

On a side note, you probably know your FC level is much to low right? I would add some liquid chlorine right away for a target of 5-7 ppm.

 

[Jimrahbe]

Senex.

Did replacing the cartridge make things better for a day or so, or did it have no impact at all..??

I find it impossible to believe that with an FC of 1 you don't have algae, even if you can't see it yet.

Where do you normally keep your FC??

Thanks,

Jim R.

 

[senex]

Thanks for the ideas. I've never gone into the heater. I wonder how hard that might be.

And yep, I know my FC is low -- due to the low water flow and chlorine so expensive, that I kind of "let it go" this week, thinking the new cartridges would solve my flow problem, after which I would slam and fix the chemistry.

 

[Texas Splash]

Jim makes a great point ...... algae. New filters or not, no amount of mechanical filtration will help water over-saturated with organics. So before you go tearing into anything, it would be a good idea to do an Overnight Chlorine Loss Test. Pass that first then go into other areas if needed.

 

[ajw22]

Have you ran your system with no cartridges in the filter and see what flow you get?

Check the impeller and see it does not have debris in it.

 

[mas985]

Have you noticed a change in filter pressure either higher or lower? If higher than normal, the issue is likely on the pressure side of the pump and if lower than normal, the issue is likely on the suction side of the pump.

 

[JamesW]

What speed are you running?

Can you report the following at several speeds?

Speed....Filter Pressure....System Pressure....Watts of Power....GPM.

1500

1725

2350

2750

3000

3110

3450

 

[JamesW]

Can you show pictures of the system?

 

[JamesW]

 

[JamesW]

Your old "good" numbers put your System Curve at about curve "A", which is not great.

Your "Bad" numbers are about H = 0.0592F^2, which is close to curve "B" and that is really bad.

Curve "C" is about what a good system should look like.

So, you probably have a restriction in the lines or maybe a clogged impeller.

The filter cleaning was a great victory -- I'm now very satisfied with the Intelliflo performance. Thanks to everyone for helping me solve my problem!

Some photos & data are below if you're curious.

It was difficult to remove the fins due to lack of clearance (the manual recommends 23" of clearance above the unit and I have 11"), but I managed to tilt it out. The fins looked like this (the clumps of DE are 3/4" to 1" thick):



This was after I had backflowed 3x to try to flush the DE. (Afterwards I realized that I had only been backflowing at 2600rpm, not the full 3500+, so maybe my backflows were substandard).

I'm not sure if that's a "normal" amount of DE for after a backflow, but it seemed excessive to me. As previously mentioned, it's been at least one year since the last cleaning, possibly much longer.

I followed TFP's [link=[URL="http://www.troublefreepool.com/threads/72506-DE-Filter-Cleaning-Tutorial]DE"]DE Filter Cleaning Tutorial[/URL] Filter Cleaning Tutorial[/link]. Everything went smoothly. It took about 3 hours of work because I went slowly & carefully (it's my first cleaning). I especially like the advice to mix the DE into a slurry before pouring into the skimmer. Our prior pool guy (before I found TFP) used to pour the powder directly into the skimmer, and I wonder if that promoted clumping on the filter fins.

The flow numbers look excellent after the cleaning:

--------------- Before DE Cleaning ------------------------------------------------------------- After DE Cleaning ------

RPM	Watts	GPM	PSI		Watts	GPM	PSI
1000	62	7	3		60	5	3
1600	190	12	8		242	25	8
2000	364	18	13		490	39	12
2400	670	27	19		840	50	18
3000	1340	41	29		1630	64	28

In some cases the flow doubled! This is terrific. I'm now going to get the 80%+ energy savings I anticipated -- and the much quieter operation.
(The flow at 1000rpm actually decreased, but I think that's because I still had air in the pipes when I took the new measurements at low rpm -- so I'm not concerned).

Thanks again for the great advice here.

Disappointed with Intelliflo VSF gpm at low rpms

I got an Intelliflo VSF installed yesterday (I haven't updated my signature line because I forgot to write down the model number this morning). The pump has a digital readout of RPM, Watts, GPM, and PSI. I recorded some values this morning: RPM Watts GPM PSI PSI on DE Filter Gauge 1000 62...

www.troublefreepool.com

y=0.016(X)^2, y from 0 to 90 - Wolfram|Alpha

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[JamesW]

You can install a flow meter if you want a second way to check the flow.

You can install a vacuum gauge to see what the vacuum pressure is.

 

[senex]

Thanks for the ideas. I normally keep my FC at 3.0.

The low flow persisted even *immediately* after replacing the cartridges -- like, within 2 minutes of finishing the cartridge replacement operation.

This morning, when I made limited measurements immediately after replacing the cartridges, I had:
2200 rpm -- 25 gpm
2600 rpm -- 31 gpm
3200 rpm -- 33 gpm

JamesW -- thanks for the pump analysis. Tomorrow I can gather the full numbers and photos.

It sounds like I need to check both the impeller and the heater. Is it easy to inspect/access the impeller without removing the pump from the system?

 

[ajw22]

Is it easy to inspect/access the impeller without removing the pump from the system?

You can try and reach the impeller from the pump basket but to fully check it you will need to crack it open.

 

[senex]

Ok, thanks. Unfortunately I'm traveling next week and my regular pool guy moved away, so I'm not sure when I'll have time to disassemble the pump or plumb a bypass for the heater.

If it's helpful to understand my plumbing, I gathered some watts/gpm/psi numbers in recirc mode back back when I had a DE filter (and thus a multiport valve) when I installed the pump.

In recirc (filter bypass) when VSP was installed:
1000 rpm -- 65 watts -- 9 gpm -- 3 psi
1400 rpm -- 175 watts -- 22 gpm -- 6 psi
1600 rpm -- 270 watts -- 30 gpm -- 8 psi
2000 rpm -- 530 watts -- 44 gpm -- 12 psi
2400 rpm -- 901 watts -- 57 gpm -- 17 psi

I no longer have the multiport, and I didn't have time today to disassemble the filter a second time to test my system with no cartridges. But nothing has changed with my plumbing, so the above numbers probably represent my plumbing (plus the inline heater resistance) as of a few years ago.

 

[JamesW]

This morning, when I made limited measurements immediately after replacing the cartridges, I had:
2200 rpm -- 25 gpm
2600 rpm -- 31 gpm
3200 rpm -- 33 gpm

Those numbers are really bad.

Check the heater thermal regulator and look into the thermal regulator hole to see if the heater’s internal bypass valve is intact.

 

[JamesW]

Is the new filter plumbed correctly?

Sometimes the "In" and "out" are reversed.

 

[JamesW]

Do you still have the Pentair 320 tab feeder?

Sometimes the Mastertemp's internal bypass valve will break loose and the plunger can go into the plumbing and it will get caught in the feeder inside the pipe and block the flow.

 

[senex]

JamesW, thank you for the many ideas.

Filter is plumbed correctly in/out. Tab feeder is still in place, but is not the problem because low flow persists when bypassing the tab feeder (routing all return water to hot tub).

I will try the heater bypass tonight if I have time.