Pressure never goes up much on the filter

JasonLion

TFP Expert
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May 7, 2007
37,880
Silver Spring, MD
#1
My pressure gauge never seems to go up very much, even after I *know* the filter needs backwashing. For a long time I thought that the gauge was broken. Last week I finally got around to replacing it with a new one. The old one always read between 5 and 7, the new one mostly reads between 8 and 10. Then I got a PoolPilot SWG, which has a strainer in the manifold. Every couple of days the low flow warning goes on, I open up the manifold and the strainer is totally stopped up with the usual kind of crud I see in the skimmer sock. I didn't think that kind of stuff is supposed to get past the filter (the SWG manifold is last, between the heater and the return).

That got me thinking that perhaps the sand filter was channelized. So I opened up the filter, which by the by is so old that you can't even find a parts diagram on the web, let alone actual spare parts, and was rather surprised to see sand that looked just fine, a few stray pine needles and otherwise pristine (I had just backwashed). From the age of the pool and what I have read I was thinking that it would all be crusted over and clumped up. Apparently the sand was replaced fairly recently, well last several years anyway.

Then today, out of nowhere, the pressure drops to 6. I checked the pump impeller and it seemed fine. The PoolPilot always shows sufficient flow (if I have cleaned the strainer). Nothing about the valves or return has changed, the skimmer isn't blocked. Later in the day, playing with the PoolPilot, I ended up turning the pump on and off several times and each time the pressure gauge reads a different number between 6 and 10. Each number is steady, I can change it by turning off the pump, or playing with the valves, but leaving those things alone it stays steady until the next time I turn the pump off and then on again.

There was one other strange thing, when the pressure is 6 but not otherwise, there is an occasional irregularly repeating clank sound from the main valve. The main valve is ancient, one of those metal pull up for normal, push down for backwash, affairs. The pool inspector, when we bought the house, said that the filter and main valve were so old they stopped stocking the spare parts ten years ago, and they sure look the part. The pump is somewhat newer, but also ancient. Also, water slowly leaks out of the backwash pipe any time the pump is running.

I'm starting to suspect that this means the main valve is leaking internally, so some of the flow bypasses the filter entierly. I would rather not have to replace the main valve, as that looks like a fair amount of pumbing. More than that, I would *really* hate to go through all the work of replacing the valve only to still have problems with the manifold strainer constantly clogging. Any thoughts?
 

JohnT

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Mod Squad
TFP Expert
Apr 4, 2007
9,466
SW Indiana
#5
If debris like that is getting by the filter, something major is wrong. You have a valve in what I'm guessing is your waste line, which is a sign of previous filter valve problems, and that's where I'd guess your problem is. Possibly as the filter gets dirty, more and more water is sneaking past the valve back to the pool, allowing the pressure to remain constant.

That valve is probably repairable, but economics and availability of seals will dictate whether it's worth your time.
 
OP
OP
JasonLion

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
#6
I took apart the main valve. The lower O ring has considerable errosion, though it is still intact. Also the metal grove the lower O ring sits in has significant errosion around the edge. Everything else looks to be in good condition. In filter position the lower O ring seals the pipe between the filter input and output. So I think we have most of the problem. The upper O ring looks fine, so I don't know why the waste pipe leaks slowly all the time.

Taking it apart I think I figured out what the intermittent noise was. In most positions the main plunger has some side to side play. There is only a short segment of the vertical travel at each end where it is steady. It is actually quite tricky to get it into that steady position. I suspect that most of the times I moved it I failed to get it to seat into the narrow section of the tube where the O rings actually make contact all the way around. When it isn't quite seated it can move just enough to make the dull clanking noise I was hearing before.

I looked around for spare parts. I'm sure I can get O rings that are close enough, but replacing the main rod/plunger (all one piece) seems fairly hopeless. The part number on the outside appears to be WC12-18D, which is somewhat similar to some old Sta-Rite part numbers. Searches on that don't turn up anything. This is similar to the situation with the sand filter. I can find some Sta-Rite sand filter parts diagrams at sites of companies who stock old parts, but none of them actually match. Looking through the valve diagrams I can get fairly close, but again nothing matches exactly.

I am hoping that if I replace the O ring I might be able to limp along for another season or two. Soon enough it is going to be time to replace the entire pump, filter, valve setup. If the budget allows, that would be a nice project for some relatively warm week next fall/spring when the pool isn't open.
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,466
SW Indiana
#7
JasonLion said:
I took apart the main valve. The lower O ring has considerable errosion, though it is still intact. Also the metal grove the lower O ring sits in has significant errosion around the edge. Everything else looks to be in good condition. In filter position the lower O ring seals the pipe between the filter input and output. So I think we have most of the problem. The upper O ring looks fine, so I don't know why the waste pipe leaks slowly all the time.
I'd try something like JBWeld to repair the metal. I've fixed an intake manifold on a truck with that stuff. You can put it on and wait for it to cure, then file or grind or saw it to the right shape and finish.