Filter Size vs Pump Size

[Wrisk]

Howdy.

I have had my pool for about 9 months now and have had almost no problems. I have had a few people tell me that my filter is to small for the size of my pool. My pool is rectangular, 39x19, 30,500 gallons. I have a Hayward Super-pump 1.5 hp. My filter is a Hayward c900. I am being told that i need to upgrade to a c1200.

Does this sound right?

[PoolDoc]

. . . membership upgraded

I'd recommend you actually measure your pool -- I check registration addresses on Google Maps as a method of keeping spammers out (I'm the only one who can see that info -- not even the moderators have access), and your pool doesn't look like a 30k gal pool. Pool builders, home sellers and realtors tend to overstate pool volumes, sometimes by 100%.

Measure the length, width, actual water shallow depth 1' from wall and actual water deep depth 2' from the wall, and post that info. I'll recalc volume.

Regarding your pump & filter -- a C900 is a little small for a 30k gallon pool, but it's way to0 small for a 1.5hp pump.

If your pool gallons are what I'm guessing, the best option would be to size your SuperPump down. If you'll look at page 11 of the Super Pump manual, you'll see that the ONLY difference between a 1.5 HP pump, and a 1/2 HP pump is the motor and the impeller. A 1.5 HP motor can operate at any lower output level. So, you can downsize your pump simply by changing the impeller. You'll want to change the seal, too, but in theory that's not necessary.

A C900 will operate very well with a 1/2 or 3/4 HP pump . . . and you'd cut your electrical bill in half or more!

[Wrisk]

Okie dokie. My pool is 39' x 19'. The shallow end is 3 1/2 feet and the deep end is 7 1/2 feet. I hope this helps.

[CarlD]

Okie dokie. My pool is 39' x 19'. The shallow end is 3 1/2 feet and the deep end is 7 1/2 feet. I hope this helps.

It depends on the shape of the way it reaches 7 1/2'. But, ballparking, I'd guess your pool to be 30,000 gallons...or less.

Ben, the specs for the 1.5 Hayward SuperPump have 83gpm at 20' of head, and just reaching 90gpm at 10'. The C900 has a max cap of 90gpm as well. So while we all agree a bigger filter would be appropriate, it seems to me the C900 is just banging on the door of being too small but isn't quite there.

So what am I missing????

[PoolDoc]

39 x 19 = 741 sft

considering the top 3.5' of the pool, the volume would be 741 x 3.5 x 7.46 gal/cft = 19,347 gal

Generally, the average depth of the hopper and slope area is about 1/2 of the difference between the shallow depth and the maximum depth. Generally, the break is about 1/2 of the way toward the deep end (2/5 on shorter pools with a board). So:

19 x 19.5 x 0.5(7.5 - 3.5) x 7.46 = 5,527

5,527 + 19,347 = 24,874 or ~25,000 gallons. PF = 4.8

[Wrisk]

So..... The pool volume is 25,000 ish? Cool. Just for info, since I put in a new cartridge the pool is crystal clear. No issues. I just have "helpful" people telling me to get a bigger filter. It sounds like I can put that off for a bit. If I get a c1200, is the 1.5 hp pump ok? Or should I still down size?

[PoolDoc]

@ Carl: Correct vs incorrect flow rates:

[PoolDoc]

So..... The pool volume is 25,000 ish? Cool. Just for info, since I put in a new cartridge the pool is crystal clear. No issues. I just have "helpful" people telling me to get a bigger filter. It sounds like I can put that off for a bit. If I get a c1200, is the 1.5 hp pump ok? Or should I still down size?

As you can see, in the post responding to Carl, the optimal flow rate for a C1200 is 45 GPM or less, far less than the 90 GPM Carl referenced. I'd recommend downsizing the pump, and saving the electrical costs.

Be VERY CAREFUL to clean your new cartridge promptly, when the pressure begins to rise -- don't wait till it's gone up 6 or 7 pounds. The C900 cartridge is more resistant to pleat collapse than the StaRite System3 cartridge shown above, but one it occurs, it's often irreversible. Unlike sand filters, there is no benefit with cartridge filters to allowing the pressure to rise. With sand filters, the dirt becomes part of the filter media during the last half of the filter run. This is not really true, and not at all needed with cartridge filters.

Instructions on how to clean your cartridge, without damaging it, can be found here; http://pool9.net/cart-clean/

[PoolDoc]

@Carl: You need to go by the COMMERCIAL rated flow, not the residential flow. This is true on all three types of filters (sand, DE, cartridge). The commercial rates are based on actual performance data; the residential rates are -- as far as I can tell -- simply WAG's that the manufacturers were able to bully past the NSF.

Consider: As you know, the load (people per 10k gal) is GREATER on AG pools, than on IG pools. Thus, the filter loading with 8 hour turn-over flow is greater on AG pools, than on IG pools. Yet, the NSF rating for AG pools (gpm/sft) is HIGHER than it is for IG pools, even though it should be LOWER, given the greater load.

=> With sand, excess flow blows the dirt through the filter AND blows sand out of the filter when backwashing.

=> With cartridge filters, excess flow leads to excess pressure differential across the filter pleats, leading to pleat collapse, as shown in the picture below, where the pleats have collapsed against each other, blocking flow into the 'valley' between pleats.

=> DE filters are the least sensitive to overloading, but with some filters, excess flow leads to excess pressure differential and causes collapse of the underlying grid.



(photo shows both pleat collapse and damage from use of a pressure washer (fuzzy fibers)