How low can the flow get before needing to backwash

hawkinsrt

Active member
Aug 10, 2021
27
New Jersey
Pool Size
12000
Surface
Vinyl
Chlorine
Liquid Chlorine
I have a 1.5 HP Pentair Dynamo High Performance with a Fiber Glass (sand) filter. Under normal operating conditions (pool clean, recently backwashed), my PSI sits at about 15. At 15 PSI the return jet is powerful enough to where my hand cannot easily plug it (it pushed my hand to a side or sprays up out of the water). It creates a pretty decent whirlpool. Once it reaches 19 PSI, I can easily plug it with my hand but still has enough power to resist. Then at 20 PSI, its very weak with almost no flow. The general tip is to backwash once you are 10 PSI over your normal operating pressure. I don't even think I could get past 20 PSI ever and even if I did the pool would probably be at a stand still.

So my question is: Is there a general rule of thumb to determine if your flow is so low that its negativly impacting the flirtation/circulation of the pool? During the begininig of the season (now), it can easily jump to 19 PSI after a few hours of back washing (pool extra dirty this year, on day 3 of SLAM). I don't want to backwash to often because to me it seem like sand filters are not as good at filtering right after a back wash and need a little be of debre (or DE) to help catch the smaller stuff.
 
You should backwash when your pressure rises 25% above the clean pressure. So, for your clean pressure of 15 psi you'd aim to backwash around around 18-19 psi.

 
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