Sand filter pressure rises with use then returns to clean pressure with OFF/ON cycle?

[gtemkin]

My sand filter has had odd behavior that I wondered if anyone else has seen.

The gauge goes to zero when off and is around 10psi when the pump is on and the sand is clean. If I run my suction side Kreepy Krauley after not having cleaned the pool for a week or so (there's small leaves on the bottom and maybe some unseen fine silt or dirt down there) after a few hours the gauge gradually climbs to around 15 and the Kreepy Krauley slows somewhat. So far, that's perfectly normal behavior for my equipment and I would then normally perform a backwash. However, if I don't backwash and instead, just shut off the pump and then turn it back on, the filter pressure after that quick Off/On cycle is back to a 10psi reading and the Kreepy Krauley has picked up its pace indicating the change in pressure was real. I do not see any dirt plumes coming from the returns which might be an indicator of something amiss.

So basically I'm loosing back pressure that's developed by a partially clogged filter by simply shutting the filter off and turning it back on. In one sense it's great because I don't waste water backwashing, but obviously something isn't right.

Water is very clear and numbers using TF100 are:

pH 7.6
FC 6
CC 0
TA 70
CH 300
CYA 45

Thanks


Edit: This behavior has been a happening anytime I notice the filter is starting to clog. Turning the pump Off, and then On "cleans" the filter.

 

[Patrick_B]

Mine does the same when I clean the strainer or some such thing. Can't explain it, but mine behaves much the same. I guess things just loosen up a bit.

 

[morzh]

I think when you run constant suction of finely dispersed silt it plugs the top of the sand. When you stop it, there is a backlash from the water in front of the filter and it pushes back a bit, losening and breaking up that compacted top layer.

 

[Patrick_B]

I think when you run constant suction of finely dispersed silt it plugs the top of the sand. When you stop it, there is a backlash from the water in front of the filter and it pushes back a bit, losening and breaking up that compacted top layer.

I like it. Now we need somone to pop in a Gopro to confirm it.

 

[gtemkin]

I have had what I think is fine silt on the bottom of my pool. Maybe I'll open the filter and skim a 1/4" of sand off the top. I'll also deep clean at the same time.

 

[duraleigh]

That's not uncommon for a sand or DE filter. morzh has it just about right.

When you shut off the pump the flow goes from 60-90 gpm to zero gpm in about 1/4 second. That sudden stoppage of flow dislodges the layer of debris you have been vacuuming into the filter.....almost like returning to clean pressure.