Measuring PSI to obtain TDH (ok to take PSI from sand filter?)

[rwmcmahon]

I am looking to ascertain my TDH in order to optimize my pump rpms during off season months or when I do not run any fixtures. My equipment...
- Pump: 1.5 hp Pentair SUPERFLO VS pump (model 342001)
- Filter: Hayward sand filter (model S360SX) with 2 in pipes
I am installing a vacuum gauge on the suction side of the pump. However I have some space limitations in inserting a pressure gauge at the return side of the pump.
So my questions...
If I take the PSI reading from the top of the sand filter, will that measurement be sufficiently close to the PSI measurement taken at the pump? (for purposes of obtaining the TDH)

 

[JamesW]

If I take the PSI reading from the top of the sand filter, will that measurement be sufficiently close to the PSI measurement taken at the pump? (for purposes of obtaining the TDH)

Yes, it is close enough.

 

[mas985]

I am looking to ascertain my TDH in order to optimize my pump rpms during off season months or when I do not run any fixtures.

Sounds like you might be trying to determine turnover? If so, don't bother because it really has very little impact on water quality.

Turnover of Pool Water - Further Reading

www.troublefreepool.com

The most important thing is that you run the pump fast enough for your skimmer and SWG. The SWG will tell you when the flow rate is too low by alarming and the skimmer will also tell you when the flow rate is too low by water traveling around the sides rather than over the weir door.

My equipment...
- Pump: 1.5 hp Pentair SUPERFLO VS pump (model 342001)
- Filter: Hayward sand filter (model S360SX) with 2 in pipes
I am installing a vacuum gauge on the suction side of the pump. However I have some space limitations in inserting a pressure gauge at the return side of the pump.
So my questions...
If I take the PSI reading from the top of the sand filter, will that measurement be sufficiently close to the PSI measurement taken at the pump? (for purposes of obtaining the TDH)

There is quite a bit of head loss in the filter MPV. If you want a bit more accurate number, I have spreadsheet in my signature that will use the two measurements plus a description of the plumbing between the pump and filter to adjust the head loss.

 

[Jimrahbe]

rw,

I am curious why you need to know your TDH???

I have had three pools, for well over 10 years, and have never even thought about TDH.

When you have VS pumps, it really does not matter much.

What are you wanting to do??

Thanks,

Jim R.

 

[PoolStored]

I am curious why you need to know your TDH???

I have had three pools, for well over 10 years, and have never even thought about TDH.

When you have VS pumps, it really does not matter much.

What are you wanting to do??

+

 

[rwmcmahon]

Sounds like you might be trying to determine turnover? If so, don't bother because it really has very little impact on water quality.

Turnover of Pool Water - Further Reading

www.troublefreepool.com

The most important thing is that you run the pump fast enough for your skimmer and SWG. The SWG will tell you when the flow rate is too low by alarming and the skimmer will also tell you when the flow rate is too low by water traveling around the sides rather than over the weir door.


There is quite a bit of head loss in the filter MPV. If you want a bit more accurate number, I have spreadsheet in my signature that will use the two measurements plus a description of the plumbing between the pump and filter to adjust the head loss.

Hi there,
My goal is to reduce electricity cost and preserve life of pump. For about the last 1.5 years my pool tech set my variable pump to run at a single setting of 3450 rpm for 9 hours. I can see a high rpm setting for summer when running my waterfall or slide and maintaining chorine with my SWG as well as other benefits. But during winter I am just running the two return jets (and the SWG is too cold to function). I experimented a little by manually setting my pump to 2800 rpm and could see my skimmer furthest away from my pump was still functioning which seems like a good litmus test (with main drain suction at full return as well). One thing the popped out at me was that the wattage was almost 1000 watts less then when set at 3450 rpm. I am hoping I can scale back on the 3450 rpm and take advantage of the variable speed pump and run at much lower rpm and for longer period of time if need be. I was looking to obtain the flow rate at the 2200 and 3000 rpm curves in my pump's manual.

I read the Turnover of Pool Water page before writing this response and see there is no specific number of turnovers I should be targeting. From the page, I can see 2-6 turnovers is common so will use that data.

The Hydraulics 101 in your signature which was very educational. Thank you.

 

[rwmcmahon]

+

rw,

I am curious why you need to know your TDH???

I have had three pools, for well over 10 years, and have never even thought about TDH.

When you have VS pumps, it really does not matter much.

What are you wanting to do??

Thanks,

Jim R.

That is a good question. I answered that in my response to mas985. Thanks

 

[Jimrahbe]

@rwmcmahon

Reducing your electrical costs makes perfect sense, and running at 3450 is insane!! What is the point of having a VS pump if it runs at full speed..

I think you are on the right track... As a reference, I have a 3 HP IntelliFlo that runs 24/7, mostly at 1200 rpm.. This costs me less than $20 bucks a month.

Slower and longer is always better that faster and shorter..

I like the idea of watching your SWCG and then reducing your pump speed until the cell reports low flow.. Then, slowly increase your pump speed, until the flow closes the SWCG's flow switch.. then add 100 or 200 rpm, just to make sure.. This is the slowest speed you ever want to run.. Then you can have other speeds to run your water features.

Looking at your skimmer is not a very good test, as the skimmers work due to the Weir door action, and not due to the pump speed. My skimmers 'look' like they are not working, but they still work fine.. I use hairnets in the skimmers, and they are always full when I clean them.

I would also recommend that you turn your main drain to almost closed (About 10% open) this will allow for better skimmer operation at low speeds.

Thanks,

Jim R.

 

[PoolStored]

Run your pump for a reason. Filter, mix chemicals, create chlorine, heat the water, skim etc.

I have an SWG and a heater. Heater requires 35GPM. I use a solar cover, so skimming isn't really a thing for me. I have the same pump.

2200RPM will flow 35 GPM in my system. I run 2200 RPM when I'm heating.
All other times, I run 1400RPM. Clean your filter. Reduce the pump speed until the NO/LOW Flow comes on on the SWG. Add 200 RPM for a dirty filter and run at that speed.

Unless you have something that requires running higher, like waterfall/slide, or you need skimming action, there is no need to run the RPMs you are discussion.

JimR'd

 

[mas985]

I read the Turnover of Pool Water page before writing this response and see there is no specific number of turnovers I should be targeting. From the page, I can see 2-6 turnovers is common so will use that data.

Use that data for what? That is what pool builders generally target but again, that is not useful for a residential pool and can be ignored.

Looking at your skimmer is not a very good test, as the skimmers work due to the Weir door action, and not due to the pump speed. My skimmers 'look' like they are not working, but they still work fine.. I use hairnets in the skimmers, and they are always full when I clean them.

I have two skimmers and the reason I use the skimmer weir door as one of the flow rate metrics is that if I use SWG alone, the flow rate required for the SWG is much lower than what is required for two skimmers so the water will not travel over the top of the weir door and debris collects in front of the weir doors never making it to the skimmer basket. In general, if you have only one skimmer, the SWG is probably going to be the limiting factor while if you have two skimmers, the skimmers will be.

 

[Jimrahbe]

Mark,

That makes perfect sense.. I did not mean to suggest that you should not look at the skimmer action. It will just not 'look' the same at low speed as it does at high speed. If a pool owner with a single speed pump, looks at my skimmers, they will most likely think my pump is not running..

I agree that not every pool is the same and that the "SWCG" speed may, or may not, allow for good skimming action.

In my case, both of my skimmers work well at 1200 rpm... but... I do not have a heater, and I have a large cartridge filter, with almost no back pressure.

I think it is up to the user take our ideas and to experiment with what they have, and then decide what works best for them.

One size does not fit all for sure.

Thanks,

Jim R.

 

[rwmcmahon]

Use that data for what? That is what pool builders generally target but again, that is not useful for a residential pool and can be ignored.



I have two skimmers and the reason I use the skimmer weir door as one of the flow rate metrics is that if I use SWG alone, the flow rate required for the SWG is much lower than what is required for two skimmers so the water will not travel over the top of the weir door and debris collects in front of the weir doors never making it to the skimmer basket. In general, if you have only one skimmer, the SWG is probably going to be the limiting factor while if you have two skimmers, the skimmers will be.

Roger that. Thanks for elaborating on the second skimmer and correction on interpreting the target replacement. Also the "pump run time study" in your signature was very educational.

 

[JamesW]

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