Filter pressures vs flow rate


Bronze Supporter
Aug 8, 2018
Merrick, NY
For whatever reason, I can’t go by filter PSI when deciding to backwash my DE filter: It starts at 18, goes to 20 over time, then visibly decreases flow all the while stuck at 20.

One way I’ve learned to determine my “backwashability” is whether there’s enough waterflow to engage the heat pump. Which got me to thinking (🎵“a dangerous pastime, I know”):

There‘s a thread elsewhere that discussed removing the eyeball socket from the pool return to decrease obstruction and increase flow. Yet doing that usually shuts down my heat pump. So is the issue with heat pumps less dependent on “flow” than “pressure”? (which downstream obstruction does provide, and is lacking with upstream obstruction, which happens with filters in need of a backwash).

Anyway, just some random thoughts....


TFP Expert
LifeTime Supporter
May 3, 2007
Pleasanton, CA
Pool Size
Salt Water Generator
It could be that you are operating near the top of the pumps head curve were it is very flat, so a small change in head loss results in a large change in flow rate.

The other possibility is that the gauge is bad.
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