pressure problems with new de filter

[coryinsocal]

hey all, i just replaced my vintage spin de with a pentair 36+ (my spin was only a 25sqft). this and a new multi seemed to install ok. i did a rough visual on the grids before i installed but i have that same "all my de went into the pool!" as a few others here. the pump primed fine and i filled the entire fiter quick enough, till the water came out the vent continuously, then i closed the vent and dupmed in my slurry. main issue here, i never got any pressure on the filter. none. the jets were spitting out some de as i dumped it in.

my question is, if there's a small tear or something, wouldn't you at least have some pressure and just get the de bypassing? i took the lid off and everything is at least going through the right direction (de on the outside). i'm wondering if i should be looking at the valve or if this is normally still a filter issue. it doesn't seem to be leaking from the waste port, but i guess that doesn't mean there isn't something else wrong with it.

to top it off, i forgot to switch my valve to "closed" before i vented the filter to have a look, after that, the remaining 80%of the de lot burped up out of my skimmer! lucky me, i bet that'll never happen again. everything seems to be going in the right direction, i just have about 3.5 lbs of de in my pool...

i guess another similar question, but something that would help me troubleshoot, is there normally any pressure showing before you ever add de?

[coryinsocal]

to top it off, i forgot to switch my valve to "closed" before i vented the filter to have a look, after that, the remaining 80%of the de lot burped up out of my skimmer! lucky me, i bet that'll never happen again. everything seems to be going in the right direction, i just have about 3.5 lbs of de in my pool...



come to think of it, what usually stops the filter water from flowing back to the skimmer when you want to drain the filter? is this supposed to be built in functionality of the valve or filter? or would it just be the pump impellor? normally, i hear you don't need a check valve here (i've never had one before...)

[Poconos]

From what you describe I assume you have an in-ground pool with the filter and pump above the pool waterline. If this is the case then nothing will prevent water from flowing back to the pool through the skimmer and return lines when you open the system to air. There is not normally a check valve in the skimmer line. Some situations...maybe. I don't have a DE filter so I ask, why do you want to drain the filter? If it's to work on it then I don't know how to prevent DE from backing through the skimmer. Hopefully someone with experience with DE filters will kick in. Not much help here.
Al

[coryinsocal]

From what you describe I assume you have an in-ground pool with the filter and pump above the pool waterline. If this is the case then nothing will prevent water from flowing back to the pool through the skimmer and return lines when you open the system to air. There is not normally a check valve in the skimmer line. Some situations...maybe. I don't have a DE filter so I ask, why do you want to drain the filter? If it's to work on it then I don't know how to prevent DE from backing through the skimmer. Hopefully someone with experience with DE filters will kick in. Not much help here.
Al
yup, IG, and the only reason to drain was to inspect the grids or clean the filter. not really concerned with it going back through the return (there should be de on that side). i guess i could add in a ball between the pump and filter, but this is another, more solvable issue. mostly i'm concerned with the pressure/de problem.

[Tomcat]

When I backwash and add new DE, I hardly get a pressure rise as well (maybe 1 or 2 psi).

[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...

[Poconos]

Just a comment on the pipe diameter pic. The 90 on the left looks like a drain/waste 90 deg. These are not designed for pressure. Sched-40 pressure fittings look like the 90 on the right. The PVC is thicker and the bonding length, how far the pipe goes in when assembling, is about 1.25" I believe.
Al

[coryinsocal]

Just a comment on the pipe diameter pic. The 90 on the left looks like a drain/waste 90 deg. These are not designed for pressure. Sched-40 pressure fittings look like the 90 on the right. The PVC is thicker and the bonding length, how far the pipe goes in when assembling, is about 1.25" I believe.
Al

yeah, i just posted that for the flow rate ref. it's a case study by edison. all my stuff is sched 40.