Detailed Water Flow test & simulation for my pool

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SPP

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Apr 6, 2008
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Indonesia
Guys & Gals,

This is the report of my pool with undersized piping & long piping run and how it effects the overall water flow.

I am using 2HP SF 1.0 50hz 2,850 RPM Hayward Pump ( A.O Smith motor ).
This is not as powerful as USA model at 60hz & 3,450 RPM pump of same 2HP SF1.0 label.
Bottom line is, the impeller is moving 17.5% slower than a USA model.

Anyhow, even at reduced pumping power, I am already loosing efficiency with all 1.5" PVC pipes, instead of 2".

3 valves are plumbed to the pump suction port. The valves serve :
- Vacuum, pipe length approx 13 feet. Water level to pump's impeller, approx 2 feet.
- Balancing Tank, pipe length approx 13 feet. Water level to pump's impeller, approx 6 feet
- Main Drain, pipe length approx 63 feet. Water level to pump's impeller, approx 2 feet

Normal operation is Balancing Tank + Main Drain valves fullly opened

There are two in-line plunger type check valves. One is at the pipe end of Balancing Tank and the other is about a foot below pump suction pipe. So in normal operation, the pump must overcome these two check valves.


Vacuum gauge and pressure gauge are installed on the holes/thread available on the pump's strainer housing.
So what is being read, is what the pump works against, for suction and for discharge.

PARAMETER 1. Filter condition is not so clean. Check valves installed.

Test 1
All three valves opened.
Vacuum is 8Hg, pressure is 18 psi. Flow is 47.6 GPM
Total Head Loss ( 8 x 1.13 ) + ( 18 x 2.31 ) = 50.6 feet

Test 2
Only Main Drain & Balancing Tank vaves opened. This is the normal operation
Vacuum is 11.5 Hg, pressure is 17psi. Flow is 45 GPM
Total Head loss ( 11.5 x 1.13 ) + ( 17 x 2.31 ) = 52.3 Feet


PARAMETER 2 Filter condition is not so clean. Check valves plunger & spring removed.

Test 3
All three valves opened.
Vacuum is 6.75Hg, pressure is 19.5 psi. Flow is 47.6 GPM. Power consumption 1,568 watts.
Total Head Loss ( 6 x 1.13 ) + ( 19.5 x 2.31 ) = 52.6 feet

Test 4
Only Main Drain & Balancing Tank vaves opened. This is the normal operation
Vacuum is 8 Hg, pressure is 19psi. Flow is 47.6 GPM ( flow meter a bit jumpy & i read the high jump ). Power consm 1,568 watts
Total Head Loss ( 8 x 1.13 ) + ( 19 x 2.31 ) = 52.9 feet

The result of test 1,3 & 4 are confusing, same GPM but different TDH. After removal of check valves plunger + spring and re-starting of pump, I only wait for 2 minuts before doing Test 3 to Test 6. Maybe hidden air bubbles is effecting somehow and a +-10% accuracy flowmeter .

Test 5
Only Balancing Tank valves opened
Vacuum is 11 hg, pressure is 17.5 psi. Flow is 44.9 GPM. Power consumption 1,551 watts
Total Head Loss ( 11 x 1.13 ) + ( 17.5 x 2.31 ) = 52.8 feet

Test 6
Only Main Drain Tank Valves opened
Vacuum is 17hg, pressure is 16 psi. Flow 41 GPM. Power 1540 watts
Persistent air bubble in pump strainer box
Total Head Loss ( 17 x 1.13 ) + ( 16 x 2.31 ) = 56.2 feet


PARAMETER 3
Clogging Test. Filter condition is not so clean. Check valves plunger & spring removed. All three valves opened

Total pump run time between test below and test 1, is about 6 minutes.

Test by closing the pool inlet valve slowly to simulate filter restriction

Test 7 to Test 9
Pressure 22 psi, vacumm drop to 6Hg. Flow 42.3 GPM. TDH 57.58 feet
Pressure 23 psi, vacuum drop to 5.5 Hg. Flow 33 GPM. TDH 59.34
Pressure 24 psi, vacuum drop to 4 Hg. Flow 12 GPM.... bubbles plenty in pump strainer box. TDH 59.96
With so much air bubbles at 24 psi, I doubt both gauges read correctly. At least the flowmeter reads well

Looking at 24 psi pressure and my pump nearly collapse, I think my pump is like a 62-63 feet head maximum.


PARAMETER 4
Clean Filters & new pressure gauges for both sand & cartridge filters

5 hours pump run time before I conducted the test below, hoping hidden air bubbles have gone away.

Test 10
All 3 valves Open, Check valves plunger & spring removed
Pump Suction 8 Hg, Pump Pressure 18 psi, Sand press 10.5 psi, Cartridge press 7 psi, Flow 52.9 GPM ( jumpy )
TDH 50.6 feet

Test 11
ONLY Main Drain and Balancing Tank Valves opened
Pump Suction 9 Hg, Pump Pressure 17.5 psi, Sand press 11 psi, Cartridge press 7 psi, Flow 50.3 GPM ( jumpy )
TDH 50.6 feet

Again, test 10 & 11 results are confusing. Same TDH but different GPM.


NOTE :
The gauges are not a laboratory grade, so I don't know what kind of sensitivity or error. Its sure better than the original ones I had. Now with all new gauges, the reading makes more sense.

The flow gauge I read in Liters Per Minute and I convert to gallons, it is supposed to be only +-10% accurate.


Cost of tools :
3 new pressure gauges ( 2 to replaced original Hayward ones ), 1 Vacuum gauge & 1 flow meter. Damage US$200 only.
Digital volt meter and digital ampere meter, I already got my own, so no extra cost.


Overall I am happy with knowing what's going on with my pool circulation and plumbing variables. At least I am seeing realistic GPM changes when pressure or vacuum reading changes, instead of assumed or theoretical calculated data that I could never really know/verify until today. Even though assuming my flowmeter reading is 10% off, 90% sure is better than guessing.

For those in countries with 50hz electrical supply ( like me ) and using USA made pumps please recheck your pump data sheet.
I been trying to trace USA made pump from Hayward and Pentair website, I can not get their 50hz motor pump curve. All data are of 60hz.

There is a website that can do calculation for you based on Affinity Law ( calculation for pumps ) where it will tell you how much derating from 60Hz to 50Hz unit and many more calculation. Look at the fluid section HERE


Typical GPM derating is like this for my own Hayward as per calculator :

Assuming impeller used are the same :
USA spec is : 2HP SF 1.0 60hz, motor speed is 3,450 RPM ( If this is an approx 70 GPM flow )
50hz country spec is :2HP SF 1.0 50hz, motor speed is 2,850 RPM ( it then becomes 57 GPM flow )



Typical head derating, assuming impeller used are the same.... is a very sad result

USA spec is : 2HP SF 1.0 60hz, motor speed is 3,450 RPM ( ASSSUMING If this is a 75 feet maximum head )
50hz country spec is :2HP SF 1.0 50hz, motor speed is 2,850 RPM ( it then becomes 54.6 feet maximum head )

Looking at my test result which my Hayward Super Pump 2.0HP SF 1.0 ( 50Hz / 2,850 rpm ) pump only pumped out 12 GPM at 59.96 feet of head and very likely will stop pumping at 62 - 63 feet of head, I think the equivalent of this pump in Hayward USA spec is the the 1.1HP SF 1.1 ( Model SP2607X10 Super Pump ) if based of pump head curve. I have always thought a 10% derating was enough, now it seems so wrong.

So, anyone with a pool that has TDH of 50+ feet and is from a 50hz country, please be careful when looking at USA 60hz spec sheet. Get a 50Hz spec sheet....and unfortunately I have surfed for many hours and could not get them. I am saying 50+ feet TDH as caution is because, if a 50 hz pool owner reads 60hz spec sheet and unknowingly choose a pump with 80 feet maximum head, he may get one which is close to useless water flow if pool is 50+ feet TDH. I am waiting for Pentair 50hz pump curve from the dealer. I will share when I get it, as a reference for 50hz pool owners.

If u want to see what the difference is as far as electrical spec of the actual supplied motor for Superflo 60 hz ( USA ) version and 50hz version :

Pentair Superflo
Data from Pentair website
60Hz USA SPEC MOTOR
RPM 3,450
Label HP 1.5
SF 1.65, BHP 2.47
Max Head 71-72 feet
Pump Curve : available on line
Impeller model : available on line


Pentair Superflo
Data from my own motor name plate. This is my back up pump on trolley.
50Hz MOTOR
RPM 2,850
Label HP 1.5
SF 1.10, BHP 1.65
Max Head : Unknown
Pump Curve : Unknown
Impeller model : Unknown



Regards,
SPP
 
Question to Pool Builder or private pool owners....

In the USA, when a PB builds a pool for a private customer ( non commercial ) and customer simply don't want to get involved in water flow calculation, is it a practice that the PB does a calculation sheet and when all ready, conduct a similiar test like mine, to verify to a customer the actual hours needed for turnover of their pool or at least to verify the initial estimation ?

Hooking a vacuum gauge and pressure gauge is so easy for pumps with ready prepared plugged holes like mine and preparing a flowmeter on a special rigged hose or pipe for testing is not that hard if for commercial reasons.

I don't know how much it cost you guys in the USA to build say a basic 35,000 GL in ground pool, but I am sure its not cheap.
I am beginning to regret now that I never got involved at all when my pool was built.

If I had known from day 1 that my pool water turnover needed 12 hours at least with clean filter, I could have maintained the pool easier and with better result. My PB only said the standard is 8 hours. I was wondering how that calculation came about when they even had no logic to install 2" pipes as the should, in the first place and save me at least "5 psi value" and that is a great improvement for my pool. Now I don't think I can push anymore flow efficiently by pump size upgrade, those already buried 1.5" pipes inlet into the pool are just too small and I will be pushing mainly for friction.

I am going to do a total conversion on my 1.5" pipe that does not get buried in the concrete, to be 2". I also plan to do a special shape manifold for those 3 suction valves to reduce loss. Electrity bill I can live with but 12 hours ( with a clean filter ) per turnover is a big NO NO for my pool. It is shaped so odd and without extra pool water turnover, I can't broadcast my sanitizer properly and in return I can never get the level of clarity I like.

Thanks to all that have helped me and to TFP, you guys have made me learn so much and taught me so much.

Regards,
SPP
 
A wonderful write up. You have been very through.

Flow rates usually fall off steeply as you near the TDH limit for the pump, even though the total energy/power involved remains more or less constant.

SPP said:
In the USA, when a PB builds a pool for a private customer ( non commercial ) and customer simply don't want to get involved in water flow calculation, is it a practice that the PB does a calculation sheet and when all ready, conduct a similiar test like mine, to verify to a customer the actual hours needed for turnover of their pool or at least to verify the initial estimation ?
Click to expand...

No, that is not at all common. What commonly happens is that the builder is simply copying what they did on a similar pool at some point in the past. If it worked last time, it ought to work this time. In some cases little changes that affect the design accumulate over many pools and there can be problems.

Occasionally, some one might hire a pool designer/engineer that doesn't work for the builder. They will often do the full calculation. Some builders do the full calculation and then build the same pool over and over and the calculation applies in each case. A few builders actually do the work up each time, but that is mostly just the high end custom pool companies.

You also need to keep in mind that the builders design goals are different than what you would choose. Builders use components with low prices and high apparent value. Apparent value doesn't always correlate well with actual value. For example, builders like large pumps because people who know nothing are impressed by the big number and active water flow. Builders don't typically care about saving electricity, as that isn't something buyers are concerned with when shopping around. Only after they have had the pool for months do they notice the electric bill and most of them just figure that that is what it costs and don't investigate further.
 
Ahhh, I see. Since in the USA using pre made liner is common, I understand what you mean. Here we must use concrete and tiles. So no pool will be the same unless designed to copy the other.

Thanks Jason.
 
Now let me calculate backwards for the fun of knowing what if all my pipe after pump discharge is using a 2" instead of the current 1.5". Tomorrow I will convert the suction to 2" and will make a 3" manifold to accomodate all three 1.5" valves. So I shoul not worry about suction loss for higher water flow. The only pipes I can't improve is the inlet into the pool.

Total head after pump output is 18 psi or 41.6 feet head, clean filter. Flow is 52.9 GPM.
Plumbing is calculated at 100 feet. My current water velocity is 8.3 feet/second ( on-line calculator )
Loss in plumbing of 1.5" pipe is 6.21 psi
If I use a 2" pipe, I will loose only 2 psi and my water velocity will be only 5.2 feet...beautiful for erosion control.

At 52.9 GPM, I am getting 11.3 hours per 1 pool water turnover.
If I want 8 hours per 1 turnover, I must push to 75GPM.
I will get 12 psi resistance just from water flow resistance, that is double of current resistance.
The water velocity will be 11.8 feet/second.....wow, I wonder what will that do to my pipe long terms health.

If I am now getting 18 psi with clean filter and knowing that 6.21psi is for pipe friction for 52.9GPM, at 75GPM I will
get reading of 23.79 psi. That is 55 feet of head.

Assuming my suction pipe conversion will work well and I can maintain 8 Hg at 75GPM, TDH will be 62.15 feet.
I must then use a USA equivalent of the Pentair Whisperflo 1HP ( 1.65BHP ) WFE4 and can get about 71 GPM and being in the efficient range.

The question is, how will 11.xx feet persecond of water velocity effect my piping in 10 years to come ?
If I have to redo the piping inside the concrete ( there's where they are ), I will go for broke for sure.

I now have a 1.5HP ( 1.65BHP ) Pentair Superflo on trolley as back up and to speed up turnover, which is easily a 65+ GPM real flow. I have not measure it yet but I know its better than 53GPM. With both pumps running, I can do 6 hours turnover easy.

Any suggestion guys ?
 
SPP,

Nice detailed analysis. My only comment would be that you may be worrying too much about water velocity. There are many pools with plumbing too small for the pump and never have I heard of pipes "wearing" out. There is very little abrasion in a PVC water pipe and the walls are so thick that I really don't think that this is an issue. I think most pool plumbing will well out live the pool owner and most certainly the other pieces of equipment.
 

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PVC pipe is very sturdy. It doesn't erode at high flow rates the way some metal pipes will. Nor is it sensitive to the amounts of water hammer likely in pool plumbing. The "maximum" water velocity isn't really a limit, just a nice design guideline for reasonable efficiency. The faster you move water through the pipe the more energy you are losing to friction. Other than that there aren't any real problems till several times the "maximum" flow rate.
 
On other thoughts, I am unhappy with the ALL 1.5" pipe my PB installed.
Electric power in my country just went up by 40% my wive said yesterday...not good news.

I just don't understand, why can't my PB simply follow Hayward guideline for 2" pipes on a 2BHP pump...my my.
If they don't want to learn, at least just follow the Hayward pump sizing guide, after all they sell Hayward.

I now can't push more flow without loosing a lot in friction....what a waste :x
 
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