Sand filter clean pressure jumped from 12 to 17 psi

[calinb]

Our pool filter has been working hard this year. First, I opened to a green pool. I think it was related to the late season Jack's #2 treatment I did last year and using only Polyquat 60 instead also first shocking with chlorine before closing. I had fears of stain re-deposition with the addition of too much chlorine immediately after concluding the treatment.

Since opening and getting the pool cleaned-up, we been hit by two extensive thunderstorm periods, and they always blow all kinds of organic debris into the pool in the forest where we live. Of course we have tons of pollen falling from the sky this time of year too.

So I've been back washing a lot! After a recent back wash, I could not get the pressure drop in the filter to fully recover down to its usual 12 psi minimum. No matter how much back flushing I did, it would not drop below 17 psi.

Next I tried a deep cleaning. The sand looked normal (no channels) and I dumped a quart of ProTeam FIlter Magic into the filter, manually agitated it in the sand a bit with a stick, and let it sit overnight. Just this AM, I started the pump with the filter in back wash mode and blew out any remaining yucky stuff. This process has previously resulted in perfectly clean sand for me but this time the pressure still sits at 17 psi.

With the returns pointed at the surface, the amount of surface agitation of the water visually appears to be normal, so I'm not losing a ton of flow, but something is wrong. Either the filter's internal plumbing is obstructed (laterals?) or the pressure gauge suddenly started reading high.

Any suggestions what to try next? (Remove all the sand, plumbing and laterals from the filter for inspection? Arrgh!) LIve with it? I'm still trying to get the sparkle and "polish" back on the water after the last thunderstorm and pollen drop so I'll see how long that takes.

 

[duraleigh]

Any suggestions what to try next?

If you can find NO reason for the increased resistance (eyeballs, valves not open fully, etc) about the only conclusion is a bad gauge. Does it go to zero when the pump is off?

 

[calinb]

If you can find NO reason for the increased resistance (eyeballs, valves not open fully, etc) about the only conclusion is a bad gauge. Does it go to zero when the pump is off?

Thanks very much for your prompt reply, duraleigh! The gauge reads zero when the pump is off. I can't discern anything visibly different from before, other than the gauge reading. Gauges are relatively inexpensive so, out of curiosity, I think I'll order another one. Accuracy isn't important but repeatability is certainly useful!

The waste dump port volume looks normal in the multiport valve "backwash" and "rinse" positions. The volume delivered to the surface via upward angled return eyeballs looks normal (of course stronger with the multiport valve set to "recirculate" than when it's set to "filter" but that's normal). The increase from the normal 11 to 12 psi that I'm inexplicably seeing on the gauge (about a 50% increase) is large. If the filter is dirty and the pressure gets that high, I would normally witness a decrease in surface agitation near the return eyeballs, indicating a decrease in water flow, so perhaps the pressure reading increase isn't real.

If I change my mind, I'll have to tear down the filter and remove the cover from the multiport valve to investigate for blockages, I guess.

 

[duraleigh]

tftestkits has a glycerin filled gauge that is quite accurate, repeatable and easy to read. If you are going to get a new gauge, I would suggest the one they have.....it's pretty good.

 

[calinb]

tftestkits has a glycerin filled gauge that is quite accurate, repeatable and easy to read. If you are going to get a new gauge, I would suggest the one they have.....it's pretty good.

Thanks for the heads-up, duraleigh. The 0-30 psi scale makes more sense than my current 0-60 unit. Most of these meter specs express error as a fraction of full scale deflection--at least in part. I'll need to order TF-100 refills and other maintenance hardware soon so it'll help to to qualify for free shipping!

 

[calinb]

I compared the readings against a second gauge and they agree well so it appears that I've got a partial blockage somewhere. At least the evidence points to it NOT being in the return plumbing! Strangely, the high pressure is not present when reversing the flow through the filter.

Multiport valve setting                                Pressure

"Filter"  (filtered water directed to pool returns)     high
"Backwash" (backwashed water directed to waste)         low (~same as previous filter pressure)
"Rinse"         (filtered water directed to waste)      high

So, for some reason, the pressure is normal when the water runs backwards though the filter (less resistance/obstruction when water runs backwards). Maybe that's normal. I've never paid attention to the pressure gauge reading when backwashing before.

I guess I'll pop the handle and top off the multiport valve and have a look inside before I resort to removing the top from the sand filter and removing the sand to expose the plumbing and laterals.