Sand filter pressure drop

[guamguy]

I've noticed something strange (maybe) with my sand filter. The other day, I vac'd the pool, afterwards I checked the filter pressure to ensure
I didn't need to backwash. Pressure was up to about 28psi, clean filter is about 20. Looked again a few hours later, same 28 psi, so I didn't do anything, shut the pump off for the day. Today I started the pump, and pressure is down to 22 and holding, flow from the returns is good and strong, and the gauge is good (I tested it at work against a calibration standard). I've noticed this once or twice in the past, but is it normal for a sand filter to behave this way? All chemistry is right in line except for slightly high TA, and the water is crystal clear and sparkling. I do not have any DE in the filter right now, and seems to be filtering the water just fine.
Have a great 4th of July weekend

 

[dmanb2b]

Chalk it up to a mystery...keep your eye on it from time to time and enjoy your 4th!!!

 

[duraleigh]

same 28 psi, so I didn't do anything, shut the pump off for the day. Today I started the pump, and pressure is down to 22 and holding,

My sand filter does something very similar but not as dramatic.

From time to time my normal psi of 10 will climb to 12. It takes a while and it goes up smoothly so I feel like it is junk accumulating on the top of the sand bed restricting flow. Frequently, I can shut it off for just a few minutes, turn it back on and the psi has returned to 10.

In my case (and perhaps yours) I think it is caused by dirt accumulating and layering the top of the bed. Then, when you shut it off or on, the resulting turbulence inside the filter breaks up and disturbs that very fine layer on the top and the resistance in the filter returns to normal.

After all that, I think I like dman's response as well or better than mine!!