Filter pressure drops instead of rising after running?

syedsam

syedsam

Member
So usually when my sand filter gets dirty, the pressure gauge climbs. But lately I notice the opposite I start at 15 psi, and after a few hours it drops to like 8–9 psi. Water flow still seems okay but not perfect. Anyone ever seen this before?
 
Yeah, that can happen if the pump is sucking in air somewhere. As the air accumulates in the filter, pressure drops instead of rises. Check pump lid o-ring and any unions before the pump.
 
I’d also double-check the gauge itself. Sometimes a sticky gauge gives misleading drops. Swap it out for a cheap new one before diving into major repairs.
 
Could also be channeling in the sand water finds easy paths, lowering resistance and lowering pressure. If it’s been years since you changed sand, it might be time to deep clean or replace.
 
I’ve actually run into something similar once. A steady pressure drop usually points to something disrupting the pump’s ability to maintain consistent flow. Air leaks, like Manikshaw mentioned, are a common cause, but another thing to check is whether your pump basket or impeller is getting partially clogged and then clearing itself as debris shifts around.

That can cause pressure to dip instead of climb. Also, make sure the water level in your pool is high enough and the skimmer weir isn’t sticking, because low water level can let the pump draw in a bit of air over time. If those all check out, I’d also take a look at the gauge itself, sometimes a failing gauge gives odd readings and makes you chase a problem that isn’t really there.
 
I’ve seen the same drop in pressure too! It’s usually a sign of a blockage somewhere, like air entering the pump or the sand channels being blocked. I once swapped the gauge first to see if that was the issue, then checked the pump basket and impeller for debris. It helped! Anyone else check the pump basket as a first step?
 
I had almost the same head-scratcher a while back, and it turned out to be the multi-port valve. The spider gasket inside mine had worn down, so the water was slipping past in weird ways, and the gauge would drop instead of climb.

At first, I thought it was air leaks or the sand, but once I replaced the gasket, the pressure readings returned to normal. If you’ve ruled out the easy stuff like the basket or gauge, it might be worth giving the valve a close look.
 
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