HELP! my pump just died (lots of questions here)

[Ken and Laura]

I need to replace my dead pump.

I have been considering two-speed Whisperflo but have a couple of questions I hope someone can respond to:

1. First: any general recommendations for/against Pentair pumps?

2. A local pool store recommended against a two speed because the slow flow would encourage dirt and algae to build up on the liner. Any thoughts on this theory?

3. Do the two-speed model pumps (i.e. WhisperFlo or SuperFlo) require some sort of additional (no doubt expensive) pump controller to switch it between high and low speed or is this EASILY done manually (i.e. by simply flipping a switch)?

4. I also wish to use a salt water chlorine generator. Will running a salt water generator with the pump predominantly on low speed cause the cell in the generator to wear out faster? In other words - does the reduced water velocity through the cell cause the chlorine level inside the cell to get very high, resulting in increased speed of cell corrosion?

5. Now for the biggie - what size pump to get. The current dead pump is a 20 year old ITT Marlow Argonaut but I don't know what size because the nameplate corroded away. Someone elsewhere thought even a 3/4 HP WhisperFlo might be oversized for our setup. I know it might be impossible to offer a definitive solution based on a description of what we have - but here are the pool and plumbing particulars in the hopes that some fluid dynamic expert out here might take a whack at it:
-18 x 36 oval, guessing about 22,000 gallon
-Filter is 3.1 SF sand rated for 47 to 61 GPM, 50 PSI max
-Pump/filter located about 40 feet from skimmer/main drain side of pool
-1 skimmer and main drain, two returns at opposite end - all 1.5 inch PVC
-Supply lines converge at Jandy valve at pump inlet
-Filter has a side-mounted multiport valve
-Vacuuming is currently done manually – but there is what I think is a vacuum inlet in the side wall of pool that is stubbed out and capped next to the multiport valve (my guess is previous owner planned for future auto vacuum but never got around to it)
-pump is probably about one or two feet below skimmer level because water flows out of pump basket (from skimmer?) when you open it.
-Everything else is the standard elbows etc. you’d need to run the pipes as described

Responses to these issues/questions would be very much appreciated!!

Thanks

[mas985]

I need to replace my dead pump.

I have been considering two-speed Whisperflo but have a couple of questions I hope someone can respond to:

1. First: any general recommendations for/against Pentair pumps?

If you go with Pentair, I would go for the Whisperflow line of pumps. They are pretty efficient.

2. A local pool store recommended against a two speed because the slow flow would encourage dirt and algae to build up on the liner. Any thoughts on this theory?

Not sure how they get to that comment but you will have to run the pump twice as long on low speed as high speed. Maybe this is true if you run the pump for the same length of time.

3. Do the two-speed model pumps (i.e. WhisperFlo or SuperFlo) require some sort of additional (no doubt expensive) pump controller to switch it between high and low speed or is this EASILY done manually (i.e. by simply flipping a switch)?

Either way. A controller will allow you to automate the high speed and low speed run times, otherwise you can just use a switch to manual change speeds.

4. I also wish to use a salt water chlorine generator. Will running a salt water generator with the pump predominantly on low speed cause the cell in the generator to wear out faster? In other words - does the reduced water velocity through the cell cause the chlorine level inside the cell to get very high, resulting in increased speed of cell corrosion?

No. As far as I know, the reduced velocity through the cell does not affect the performance. However, given the longer run time of the pump on low speed, you will need to set the chlorinator %/power accordingly.

5. Now for the biggie - what size pump to get. The current dead pump is a 20 year old ITT Marlow Argonaut but I don't know what size because the nameplate corroded away. Someone elsewhere thought even a 3/4 HP WhisperFlo might be oversized for our setup. I know it might be impossible to offer a definitive solution based on a description of what we have - but here are the pool and plumbing particulars in the hopes that some fluid dynamic expert out here might take a whack at it:
-18 x 36 oval, guessing about 22,000 gallon
-Filter is 3.1 SF sand rated for 47 to 61 GPM, 50 PSI max
-Pump/filter located about 40 feet from skimmer/main drain side of pool
-1 skimmer and main drain, two returns at opposite end - all 1.5 inch PVC
-Supply lines converge at Jandy valve at pump inlet
-Filter has a side-mounted multiport valve
-Vacuuming is currently done manually – but there is what I think is a vacuum inlet in the side wall of pool that is stubbed out and capped next to the multiport valve (my guess is previous owner planned for future auto vacuum but never got around to it)
-pump is probably about one or two feet below skimmer level because water flows out of pump basket (from skimmer?) when you open it.
-Everything else is the standard elbows etc. you’d need to run the pipes as described

Responses to these issues/questions would be very much appreciated!!

If you have no spa or water features, then I would go with as small a pump as possilble. For an 8 hour turnover, you only need 45 GPM which is quite low. So a 3/4 Whisperflow will probably give you more than that at high speed and slightly less than that at low speed. If you had the current pump braking HP and filter PSI, I could give a better idea. To calculate head loss from plumbing configurations is usually very difficult and time consuming.

If you want a swag, use 60 feet of head for high speed and 15 feet for low speed. This relates to 60 GPM at high speed and 30 GPM at low speed. Your flow should be better than that.


Thanks

See responses above.