Moving to Cartridge Filter - Opinions and Math Help Needed

[RandomEvents]

Hi!
After reading the forums for the past year, I need some help that I can't quite figure out from previous forum posts.

Equipment -:
Installed a doughboy 18'x34' with ~7' deep end (~21K gallons) last year, and it came with a sand filter (silica II) and a 2hp pump (20amp 115v). (1) 1.5" return line, (1) 1.5" suction line. Run the pump eight hours a day. Lines will be within 10' of outlets/inlets (ports?)

I want to replace the the sand filter and pump with a cartridge filter and more efficient pump. From what I've been reading, I should go with something bigger than the XStream 150, and this is where I get confused. If I go for a larger filter (425?), will I not be able to give it the pressure it needs? The more I read about the GPM and Design Flow Rate, the more I get confused.

Please Help!

Thanks.

 

[Bama Rambler]

Welcome to TFP.

With a cartridge filter there is no minimum amount of flow or pressure that it needs. You can practically go as large as they make and use as small a pump as they make and it'll work just fine.

You don't say where you're located but if your electric costs are below about 20¢ per kwh look at about a 1hp SFHP 2-speed pump, and if they're higher than that you might want to look into a VS pump.

 

[RandomEvents]

Thanks for the reply Bama,
I did the math and my total cost per kWh is ~0.13 (live near Baltimore, MD)

A couple of questions -:
1) What's the second speed on 2 speed 1 or 1.5 hp motors? I can't seem to locate that info in the Hayward manuals
2) If 1.5 inch pipe is limited to 44gpm, is all that extra power from the pump a waste?
3) Am I better served by installing a second skimmer on the other end of the pool?
4) How large is large enough, 525 700?
5) Any recommendations on equipment?

Thanks for you help!

 

[Bama Rambler]

1) The low speed is half the high speed, which is usually 3450 rpm, so low would be 1725 rpm. But it's about 1/6th the power usage.
2) It isn't actually limited to 44 gpm that's just the recommended flow rate. You can easily exceed that. Actually running a larger pump into smaller plumbing reduces the power that the pump consumes.
3) It never hurts to have another skimmer, but I'm not sure it would make a great deal of difference.
4) For a 21k gal pool a 400 sgft cartridge would be plenty large.
5) Any of the major mfg's are a good choice.

 

[RandomEvents]

Bama (I got in trouble for saying this once and I still don't know why),
Big big help, you solved all my issues.

Only one last question, would a second return be helpful?

 

[Bama Rambler]

Since you have a deep end a second return that could be aimed into the deep end would certainly be helpful. Also if you have any circulation issues a second return placed to help that would be a good idea.