Extremely High Water Pressure

[Lilsroro]

Hi guys,

I've got a Nautilus DE filter system & an old Pentair push/pull type sliding valve that services a 20,000 gallon pool. Lately, whenever I turn on the pump, the water pressure in the filter starts off at its norm of 15 psi and then, after a couple of minutes, a loud bang can be heard in the vicinity of the return line/ valve and the pressures jumps to 40 psi. The water in the pump skimmer stops circulating as if blocked. This happens whether or not the filter grid is in the filter, so a dirty grid is not the problem.

I took the valve stem out and it appeared to be OK. I took it to the local Leslie's Pool Shop and the manager there said that, although the seals on the valve were badly worn, he did not think the valve was causing the problem.

I stuck my shop vac hose in the return line from inside the filter housing to see if I could vacuum out the problem. Surprisingly to me, the suction from the shop vac could be felt in the intake line at the bottom of the filter housing. This made no sense to me, as I assumed that in normal recirculating mode the intake & return lines would be closed to each other. When I blocked the intake line at the bottom of the filter housing, the shop vac started pulling out a lot of water and quite a few leaves. After sucking out about 10 gallons of water, I turned on the pump and continued to have the same high water pressure problem.

Does anyone have any ideas as to the problem & the fix? Thanks.

 

[woodyp]

I think ya' still got a wad of leaves chucked up in there.

 

[Bama Rambler]

I don't know if it's leaves but there's something in there clogging up the discharge. Can you tell exactly where the bang is coming from?

 

[Lilsroro]

Thanks. The bang seems to be coming from the above ground portion of the return line just as the pressure jumps. I'm going to continue using my shop vac on the return line to see if i can loosen a clog. I still don't understand why applying suction to the return line can be felt where the intake line enters the bottom of the filter housing, but I'll assume that's unimportant.

 

[Bama Rambler]

Can you post a pic of the plumbing? That may help us figure why you're getting suction on the inlet of the filter.

 

[mas985]

Thanks. The bang seems to be coming from the above ground portion of the return line just as the pressure jumps.

Do you have any check valves in your plumbing? If it broke it could be slamming into the other port closing it off and causing the high pressure.

 

[Lilsroro]

I do not believe I have any check valves. Attached is a picture of my pool equipment. The top line is the main return line which, somewhere underground, branches out into 4 return lines to the pool. As you might can see from the photo, there is also a line for the pool cleaner booster pump which is connected to the main return line about 12 inches above the ground. Just above this connection is where I cut the return line so I could use a rubber clog buster attached to my garden hose, a product sold by Ace Hardware with is similar to the Drain King. I also stuck the clog buster in all 4 four of the return lines and the booster pump line. There was sufficient water flow to send water out of my pool's overflow lines, but the water coming out of the return lines could be barely felt, including when the clog buster was stuck in the main return line. I also stuck my shop vac in each return line, easily sucking out as much water as I wanted, but there appeared to be no debris coming out.

None of the above fixed the high pressure problem, which now occurs as soon as the filter tank becomes pressurized rather than waiting for a few minutes. The only water that returns to the pool is through the booster pump line when it is turned on. It comes back with good pressure, suggesting that there is some type of blockage in the return line underground.

[attachment=0:1ngv6vke]pool_equipment.jpg[/attachment:1ngv6vke]

 

[mas985]

From all your symptoms, it sounds like something is loose in the backwash valve. Although you said you took the valve stem to the pool store, did you inspect the valve housing for any loose parts? There could be something in one of the pipes.

Also if it is repeatable, watch the valve when you hear the bang and see if it moves at all.

 

[Lilsroro]

Yes, I believe the problem is indeed the backup valve. The top O on the valve stem, which is essentially 2 pieces of round plastic sandwiching a large rubber O-Ring, is not being kept firmly in place on the stem by its metal clasps (its over 20 years old). As the stem is pushed down to its normal recirculation position in the valve housing, I believe the O is sliding up the stem and blocking the return line. (I'm able to easily simulate this by hand). This is a little hard to detect, because when you pull the stem out of the housing, the top O will be pulled back into its proper position. Anyway that's my working theory. I'm going to replace the backup valve and I hope that's the problem.

 

[Lilsroro]

Update - I replaced the 2 rubber gaskets & 4 E-Clips on the Backup Valve and, as if by magic, no more high pressure. Thanks everyone, and especially Mark.

 

[mas985]

Awesome