Filter pressures vs flow rate

TishTash

Bronze Supporter
Aug 8, 2018
155
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....
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
20,839
Bedford, TX
Tish,

Thinking always gets me in trouble.. :mrgreen:

Heaters use a "Pressure Switch" and not a flow switch.

Thanks,

Jim R.
 
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mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,927
Pleasanton, CA
Pool Size
20000
Surface
Plaster
Chlorine
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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duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
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In The Industry
Apr 1, 2007
34,517
Sebring, Florida
It starts at 18, goes to 20 over time, then visibly decreases flow all the while stuck at 20.
In most all cases, if the flow goes down, the psi would go up. I would replace the gauge.
 
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TishTash

Bronze Supporter
Aug 8, 2018
155
Merrick, NY
I’ll replace the gauge posthaste.

I figured the term “flow” was a misnomer; “pressure” seems far more intuitive, thanks.
 
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