Replaced Pump - Poor Flow? - Help With TDH Calculation

[wdow88]

Hello All,

First time posting in the forum but I have loved all the info that this community has provided me.
I recently started helping my brother get their inground pool working.
They previously had a 1 HP Sta-Rite Dyna-Glas pump.
After comparing specs, we decided to replace it with a 1 HP Pentair Superflo since it seemed very similar.
For some reason it still seems like the flow rate is much lower then it should be. One of the skimmers barely seems to pull any debris and the returns just don't feel as strong as they do in my own pool. Unfortunately he does not recall what the performance was with the old pump so I don't have a baseline.. I am suspicious that the old pump was possibly undersized but am trying to confirm.
I tried to calculate the TDH for this setup.
23,000 Gallon inground pool
Piped with 1 1/2", unsure if this is PVC or Flex. The inlet and outlet of the pump are piped to 2".

Equipment List:
48 Sqft DE Filter
Push pull valve
Heater
2 skimmers
1 bottom drain - Skimmers and bottom drain all seem to be piped through same 1.5" line. Pool is too dirty to see if drain is clogged.
3 returns
150 ft pipe (over estimate)
1 Jandy Neverlube valve
4 straight couplings
11 45
13 90
4 Tees
Pump is at the level of the deck, so maybe 2' lift?

The pump primes very quickly and there is no air at all in the basket. The tank pressure with the 1 HP motor is about 18 PSI. This matches the value that the previous owner wrote on the tank.

If i plug these values into the calculator on Pentair's website and used some the values from Swimming Pool Feet of Head Calculations | InTheSwim Pool Blog for the equipment. The calculator says that I will require 78.7 feet of head to achieve a 40 gpm flow. The pressure that they estimate is 34.1 PSI, which seems very high, but I am by no means an expert.

Is anyone able to provide some guidance? Would switching to the 1.5 HP Superflow help fix this problem? Is there actually a problem? It seems that even that pump may be undersized given this setup. Maybe the previous owner added the heater and did not resize the pump? We have been banging our heads against the wall for over a week and just can't figure this out.

 

[mas985]

If i plug these values into the calculator on Pentair's website and used some the values from Swimming Pool Feet of Head Calculations | InTheSwim Pool Blog for the equipment. The calculator says that I will require 78.7 feet of head to achieve a 40 gpm flow. The pressure that they estimate is 34.1 PSI, which seems very high, but I am by no means an expert.

I don't think that is correct. What was the model# of the old pump? Having the same label HP does not mean they have the same head curve.

But from my estimates, the operating point should be 39 GPM @ 56' of head. This is based upon the 18 PSI filter pressure and your description of the suction side plumbing. The pressure gauge goes to zero when the pump is off correct?

Pump is at the level of the deck, so maybe 2' lift?

The deck should be about 6" above the water line.

 

[wdow88]

Thank you so much for the reply!

The old pump was a Sta-Right MPRA6E-147L.
The motors on the Sta-Right and the Pentair Superflo are 1 HP with 1.25 SF.
Based on the 1 1/2" diameter PVC and 10 hour cycle time (23,000 gallons/10 hours/60 minutes), I made assumption that the flow rate should be around 35-45 GPM it looks to me like both pumps can should be capable of proving that flow with 60' of head.
I compared the pump curves and it looked like the 1 HP Pentair pump 340038 (G) was very similar to the 1 HP Sta-Right Dynapro - "E". This curve is from the current line of Sta-Rights, but everything that I read says the dynapro is a direct replacement.

 

[wdow88]

Also, the description of the plumbing is for the whole system.
The suction side only consists of:
2 skimmers
1 bottom drain - Skimmers and bottom drain all seem to be piped through same 1.5" line. Pool is too dirty to see if drain is clogged and it is unclear how the bottom drain is tied to these lines.
75ft 1 1/2" PVC
1 Jandy Neverlube valve
1 straight coupling
4 45 elbow
1 90 elbow
2 Tees (one combines the two skimmers, the other combines that line to the bottom drain, again, all assumed)

 

[mas985]

Sounds like you are targeting a turnover rate which we do not follow on this forum. Turnover has no bearing on water quality and results in the pool owner running the pump much longer than they really need to. 2-4 hours per day is more than enough for just circulation.

The flow rate you are getting is sufficient to maintain the pool. However, the head loss (i.e. plumbing curve) is much higher than a typical pool (i.e. 2x a typical 1.5" plumbing setup). So the setup isn't exactly optimal.

 

[wdow88]

Hi Mark,

Wow that is good to know. Most resources I've seen recommend cycling the entire volume in 8-10 hours. I would absolutely love it if I can give my pump (and my energy bill) a rest this summer.
If the current setup will be sufficient, I am fine with leaving it as is. For my own curiosity's sake, why is the head loss so high for this setup how would one reduce this? Would re-piping the entire equipment skid in 2" pipe greatly improve efficiency?

 

[mas985]

It is hard to know where the extra head loss may be but just from the filter pressure, it is likely from the filter forward. The slide valves have very high head loss although that is not the entirety of the problem. It could be the unseen pipe underground as well. Can you post a picture of the pad equipment and plumbing (entire view)?

 

[wdow88]

Hi Mark,

I asked my brother for a photo so I will try to send it. I'm just kicking myself for not buying the larger pump to be on the safe side. Live and learn!

 

[mas985]

Increasing the pump size to 1.5 HP would have only got you about 3 GPM more. The problem is that with a high head loss plumbing, you really don't gain much with a larger pump.

 

[Jafarus]

Are you trying to run the drain and both skimmers full open at the same time? If so, it is likely that you will not be able to do so based on the skimmer needs. There are a number of things you can balance before making further changes. I would dial the drain back to 15% open as long as it does not cavitate your pump. You will hear a sound when it gets near cavitation. You will see a significant different in your skimmer action. As far as the returns go, You want the return jets for the pool to be just small enough (eye size) to create the circular flow required for the skimmers when the filter is near its backwash pressure. Any more than this is just back pressure on the system with no benefit. If the pool is getting circulation that supports skimming, don't worry about the returns.

You will essentially use the suction side valves to balance to the skimmer needs going forward. When you open the pool you will want to open the drain 100% but after you get through slam you can dial it back to 15% to support skimming only.

 

[wdow88]

It is hard to know where the extra head loss may be but just from the filter pressure, it is likely from the filter forward. The slide valves have very high head loss although that is not the entirety of the problem. It could be the unseen pipe underground as well. Can you post a picture of the pad equipment and plumbing (entire view)?

I attached the photos. Unfortunately it cuts out the heater which is what the return line from the push pull valve is piped too. The heater inlet/outlets are about 3' from the ground. My brother and I joked that the previous owner must have purchased10 packs of 45s and 90s and decided "well I bought these, might as well use them".

 

[mas985]

Some of that piping looks to be smaller than 1 1/2". Is that correct?

A picture of the heater side might be useful as well.

I don't normally recommend a replumb of the pad for head loss considerations but in this case it might beneficial. If you do, go with all 2" pipe. Replacing the push pull with a multi-port would also help.

 

[wdow88]

Are you trying to run the drain and both skimmers full open at the same time? If so, it is likely that you will not be able to do so based on the skimmer needs. There are a number of things you can balance before making further changes. I would dial the drain back to 15% open as long as it does not cavitate your pump. You will hear a sound when it gets near cavitation. You will see a significant different in your skimmer action. As far as the returns go, You want the return jets for the pool to be just small enough (eye size) to create the circular flow required for the skimmers when the filter is near its backwash pressure. Any more than this is just back pressure on the system with no benefit. If the pool is getting circulation that supports skimming, don't worry about the returns.

You will essentially use the suction side valves to balance to the skimmer needs going forward. When you open the pool you will want to open the drain 100% but after you get through slam you can dial it back to 15% to support skimming only.

Unfortunately it seems that the previous owner tied the skimmers and drain to the same 1.5 inch line, so unfortunately I don't have the option to moderate the flow. Good to know that we will at least be able to get through SLAM, but I guess there might be a lot of manual skimming in the future. Thanks for the suggestion!

 

[wdow88]

Some of that piping looks to be smaller than 1 1/2". Is that correct?

A picture of the heater side might be useful as well.

I don't normally recommend a replumb of the pad for head loss considerations but in this case it might beneficial. If you do, go with all 2" pipe. Replacing the push pull with a multi-port would also help.

The inlet and outlet of the pump are 2". The rest of the plumbing is 1.5". I'll try to get a picture of the plumbing to the heater, but is essentially just 90 elbows from the ground up to the inlets, which are also fit with 90 elbows. There is a backflow preventer in line between the heater and the chlorinator.

 

[wdow88]

Hello Again!

Great news, after an intense week + change of SLAM and removing the grids to vacuum to waste, the pool has cleared beautifully! We also ended up replacing the backwash valve and think this might have caused some issues. There was a plastic tab that had broken off that we believe forces the valve to sit in the proper position, but who knows for sure.

Thank you Mark and Jafarus for your help! My niece and nephew are both been very grateful as well and it's no secret who their favorite uncle is now