Sand during Backwash?

Apsuhead

Bronze Supporter
Apr 27, 2020
311
Clarksville TN
Pool Size
19250
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
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We had 4 inches of rain yesterday so I backwashed my filter and noticed sand on the ground where the end of my backwash pipe was located. My fiberglass pool was installed last November. My filter pressure has never really risen so I’ve only backwashed a few times. I use skimmer socks that catch most everything. Do I have a problem or is this normal? Thanks!
 

JamesW

TFP Expert
Mar 2, 2011
28,208
The filter has about 3.1 square feet of surface area.

The optimal backwash flow rate is about 15 gpm/sqft.

Anything over 45 gpm will begin to entrain sand into the backwash effluent, especially if you backwash for an extended period of time.

The speed should not be more than 2,400 rpm during a backwash.

The backwash time should not exceed about 2 minutes.

If you need to lose water, use waste instead of backwash.


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JamesW

TFP Expert
Mar 2, 2011
28,208
The blue shows the normal flow of water.

The red shows the backwash flow.

If you have too much flow on backwash, the water will begin to lift the sand and carry it out to waste.

FilterSandAnimated.gif

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Apsuhead

Bronze Supporter
Apr 27, 2020
311
Clarksville TN
Pool Size
19250
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
Thanks for the detailed explanation! When backwashing … I pause the pump. Turn filter to backwash, then resume pump. The pump primes and runs at a high rpm. When finished, I pause the pump again and turn filter to rinse. Then resume pump. I pause pump again and turn filter to filter when done.
I also turn off the SWG during all this and sometimes forget to turn it back on 😅
 

JamesW

TFP Expert
Mar 2, 2011
28,208
You can also set the prime duration to 0 minutes to prevent it from going too fast.

Just start at 2,400 rpm or lower.

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Apsuhead

Bronze Supporter
Apr 27, 2020
311
Clarksville TN
Pool Size
19250
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
Great, thanks. I programmed the pump to run at 1500 rpms 24/7 and at higher speed of 3000 rpms from 6-7 am and 4-5 pm everyday to skim. I did this in the spring when I set it up. Should I make any adjusts to this schedule? I just wanted to run 24/7 and to keep enough flow to keep the SWG happy and low flow light off.
 

JamesW

TFP Expert
Mar 2, 2011
28,208
I would set the Prime Duration to 0 and then select 2,400 rpm speed to backwash.

This way, you are not going to lose a lot of sand during backwash.
 
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