DE Filter Pressure Too High

[carrdon]

We purchased a house with a pool/spa combo about a year ago - my first pool!. I have a Pentair FNS Plus 60 DE Filter. The first couple times that the pressure reached, the "needs cleaning" mark, about 21 PSI, a backwash would return the pressure to the "good mark," about 11 PSI, and the pressure would slowly raise over a few months to the "needs cleaning" mark again. After several backwashes, the pressure would not fall as much, until it got to the point to where it only fell down to about 18 PSI. So I decided to open up the DE filter and clean it. There was a ton of caked DE on the grids, even after the last backwash. I took all 8 grids out, washed them off with a hose, and reassembled. When I started the system back up, bleeding the air off properly, instead of the pressure being back down in the 11 PSI range, it went up!

Now I have the following:
Pump off = 0 PSI
Valve set to Filter, drain open 50%, main pump on, booster pump off, pool mode = 22 PSI
Valve set to Filter, drain open 50%, main pump on, booster pump on, pool mode = 21 PSI
Valve set to Filter, drain closed (skim only), main pump on, booster pump off, pool mode = 19 PSI
Valve set to Filter, drain open 50%, main pump on, booster pump off, spa mode = 34 PSI
Valve set to Backwash, main pump on = 10 PSI

I loaded it up with the proper amount of DE (using a scale) and ran it for a week. The flow into the pool was fine, and it cleaned the water.

Chapter 2: The next weekend, I dissasembled the DE filter again, used DE cleaner jacksmagic, hosed it down, and had a buddy double check my cartridge assembly. We both came to the conclusion that you really can't get it wrong - small grid in the right spot, other 7 match the pattern at the bottom, upper assembly fits fine, whole cartridge slides right in onto the riser tube. Reassembled, bled, no change...pressure still too high. Added proper amount of DE, ran it for about a month. It cleaned the pool fine.

Chapter 3: Replaced all 8 filter grids with new Pentair branded. No change! Pressure still won't come down.

I don't know what to do. It doesn't make sense. I would say a clog, but all flow seems fine.

[PoolDoc]

If you replaced the complete grids, INCLUDING membranes, then this 'STICKY' may not be immediately applicable:
http://www.poolforum.com/pf2/showthr...ng-a-DE-filter

But, if you did NOT replace the membranes, it is. And, you should read it anyhow, since improper cleaning seems to be a common cause of DE filter pressure problems. OTHERWISE:

1. Make sure your gauge is OK -- it should read 0 with pump off. If not, replace it.
2. If you have in-floor cleaning returns, bypass them or open them fully.
3. Tell us what returns (and valves, and gear) you DO have down stream of the DE filter.
4. OPTIONALLY: you can cut in a Tee, with a valve on the side outlet, and then use that Tee (with the valve open) to test whether the restriction is internal to the filter and near piping, or if it's further downstream.

[carrdon]

Thanks Ben. I did replace the complete grids. I think the pressure guage is working fine, but just to rule it out, I ordered a new one today and will report back in a few when it arrives.

Don

[PoolDoc]

Sounds like a plan.

Take pictures, too!

[carrdon]

The new Pentair PN 98209800 assembly (relief valve + gauge) came in today. Much to my surprise, the gauge from the new kit looks identical EXCEPT for where the "start" and "clean" marks are. The new gauge shows "start" at about 19 PSI, whereas the old one shows "start" at about 11 PSI. Now I'm really perplexed. If I were to put the new gauge on, it would show that my 22 PSI (that I thought was too high) is about right. I have a photo that I can post, but looks like my posting permission for attachments is currently disabled.

[PoolDoc]

The vBulletin "attachment" system has caused me no end of problems, so I don't use it. You can post using Flickr, Picasa, Webshots, or any other non-porn US based photo service.