pressure problems with new de filter

[coryinsocal]

hmmm, so before the de there's no pressure on the gage? problem i've got now, is there was no pressure even after 8 of the 12 oz coffee cans of de (i know these are only 3/4 lb, but i figure that should have at least gotten me some pressure.)

[Tomcat]

Oh..........zero pressure. Bad gauge? If the pump is working, you've got to have some pressure.

[coryinsocal]

that's why i was thinking maybe valve, if the water had 2 pathways, maybe it wouldn't build pressure...

[Poconos]

Tomcat is right. The pressure gauge is located on the pump output port, or the filter inlet...same point. You should be seeing some pressure under any condition.
Al

[coryinsocal]

ok, so i realize i'm getting carried away with the stream of thought, so i'll simplify this post.

-valve works now
-gage works now

i think i need to re-ask the pressure question and i'm pretty sure that'll tell me where the issue is...

how much is the normal increase in pressure over brand new, no de on grids and grids with the recommended amount?

if it's significant, i'm realizing that my plumbing is kinda hacked and i have significantly more return than suction. my pool is about 50 years old, has a vintage 3/4 horse pump, and originally had a 1.25" suction and a 1" return. sometime, someone scabbed on an extra 1" return that just dumps over the coping.

so i filled up again, and had my wife watch the gage on the filter while i put my hand over one of the jets, it read about 2-3psi. at this time i figure there was less than half(maybe less than 1/4) of the needed de. when i let go, it goes to zero.

i'm wondering, with this small of an inlet, and minimal line backpressure, would a 36 sq ft even see much pressure until the thing had the full amount of de? i realized that i never maxed it out. i probably got to about 75%.

[coryinsocal]

here's a picture, i blame the mess on frustration, and i assure you, it never looks like this unless i've spent a good couple of days saying bad words...

***see prior post for why i added the pic.

[coryinsocal]

well, after a bunch of research, and theorizing, i've decided that the zero pressure reading was correct, yet the filter is operating correctly. a couple things are giving me low pressure. for one, i'm missing the 3 psi due to the scabbed on return. second, since i'm starting with all the small pipes, i'm guessing that my gpm is down in the <25 range. if you go to the pentair manual, they spec the 36 sqft de at 90gpm, giving it a pressure drop of about 6 psi in addtion to the rest of a standard system. at 25gpm, the curve shows less than 1psi drop across the filter. that, coupled with me only having ever put about 80% de in, gives me 0psi drop. i figure now i can cut off that ugly return addition and have a base pressure of about 4psi. does anybody see any real issue with this? i'm curious if this logic is right.

i guess the moral of the story is that, while most people say you can't oversize a filter, you can oversize it such that the pressure differentials are very small. maybe i'll have to clean it everytime it gets 5 psi over clean...