Testing a sand filter--Any ideas?

[JohnT]

I opened my pool without a hitch until I went to vacuum.

I brushed everything toward the deep end the first day, and much of the crud settled there. After a day, I went to vacuum and had huge clouds of algae shooting out of my returns as soon as I hit a patch with my vacuum.

I assumed I had a filter problem. I just got done taking everything apart, and it's flawless internally. Sand is smooth, clean and completely loose. Multiport is uniform and installed correctly.

So, anybody have a suggestion for what I can add to the skimmer to check filter operation? The algae is pretty well gone now, so it's not an option.

 

[stev32k]

My sand filter put DE in the pool when I tried to add it a few weeks ago. Turned out the O-rings on the stem of the multi-port valve were split and hard and letting water by-pass the filter. The return spring had also lost its spring and had to be replaced. Once I fixed those problems everything returned to normal. You might try dissembling the valve and see if the gasket and O-rings need replacing.

 

[mas985]

I would think a hand full of dirt should test it pretty well if dumped into the skimmer all at once.

 

[JohnT]

My sand filter put DE in the pool when I tried to add it a few weeks ago. Turned out the O-rings on the stem of the multi-port valve were split and hard and letting water by-pass the filter. The return spring had also lost its spring and had to be replaced. Once I fixed those problems everything returned to normal. You might try dissembling the valve and see if the gasket and O-rings need replacing.

The spring is my best guess now. My valve has the replaceable diverter, so I don't have any O-ring except what keeps water from leaking out by the handle. I was thinking of trying a few more washers under the spring to beef it up.

I cleaned the shaft on the valve and heavily lubed the O-ring to make sure it wasn't hanging when I let go of the handle.

 

[JohnT]

I would think a hand full of dirt should test it pretty well if dumped into the skimmer all at once.

I thought of dirt, but man I hate the thought of putting dirt in the pool on purpose

 

[JohnT]

Still no progress. I replaced the spring, quadruple checked the gasket and O-rings and the surface the multiport gasket seals against and it still does it. As soon as I build up an extra pound or two of pressure from the dirt, it comes blowing back into the pool.

 

[JasonLion]

It seems like you must have done this already, but have you looked closely at the inside of the multi-port to make sure nothing is cracked or broken internally.

 

[JohnT]

It seems like you must have done this already, but have you looked closely at the inside of the multi-port to make sure nothing is cracked or broken internally.

I have, but I can't come up with any other explanation than that right now. I've already priced a new valve, but I'm going to wait until I can pull it apart and look again this weekend.

 

[mas985]

Have you read this thread? It sounds like your issue.

 

[JohnT]

Have you read this thread? It sounds like your issue.

I have, but I have a hard time believing that the dirt could get through my sand as quickly as it does. Not to say that it isn't possible.

The sand is loose and lays smooth on top, I stirred it fairly well, and I have gotten a 10psi rise from dirt when I vacuumed the area around the drain, which I think is unlikely if a channel is opening or any other kind of bypass through the sand is happening. That 10psi rise tells me the sand is holding back the water, and I can't see how a necessarily small passage through loose sand could stay open when the outlet for the flow is such a diffuse area.

My current best guess is mechanical damage to the multiport or its connection to the riser pipe.

I've been wrong once or twice before :? , and I'll be thrilled to report back with all the details of my error here if I can just figure it out.

My current tote board has the MP at 3:2, the sand the long shot at 10:1, and the favorite, me being wrong, an ever-present possibility at even money.

 

[JohnT]

I had decided to just change the sand, but I can't find anyplace within 100 miles that's open today. I pulled the valve, and attached a 4ft section of 3/4 CPVC to the end of a hose. I turned the water on, and pushed the pipe in slowly and worked it around until the sand had been stirred and rinsed all the way to the bottom of the filter. Took about 30 minutes to do it. I figured this would at least give me some improvement. I backwashed for about 5 minutes and then rinsed for a couple, and then tried vacuuming. No improvement.

Pulled it apart again, thinking it might have been the connection between the riser pipe and the multiport. Both are rough as the installer apparently didn't take the time to clean the sand off of the riser before installing the valve. I cleaned both, and applied a wrap of rubber tape to the riser pipe, lubricated it, and put an O-ring on the pipe, hoping it would ride right at the junction when the valve was in place. I didn't expect this to seal, but I hoped it would improve my vac time a little if this was the problem. Again, no improvement :x

I can't see how to remove the disperser assembly from the bottom of the MP, but I have looked over everything I can see on the MP with no sign of a chip or crack. Even felt some of the surfaces with a pick to see if there was a crack I couldn't see.

Changing the sand is the only thing left I can think of. After that, I'm honestly at the point of just trying to decide between buying a new MP or a whole new filter.

 

[JohnT]

I'm ready to give up. I put an entirely new multiport on the thing, and no change. Emptied the filter and replaced the sand. No change. I also carefully inspected the riser pipe and laterals while I had it apart and they were all perfect.

 

[chrisexv6]

The only time Ive ever had dirt/algae shoot back into the pool was when I turned most of the suction towards my skimmer, and the filter was freshly backwashed. My theory was that the clean filter wasnt providing enough back pressure and the dirt was literally just being pushed right thru the filter and back into the pool. Not sure if that theory is valid, but once the suction was split between main drain and skimmer the issue went away.

What kind of pressure readings are you seeing on the filter gauge?

Double check to make sure the pump and multiport are plumbed correctly........I made that mistake once, plumbed the pump output to the multiport OUTLET instead of INLET. That caused all sorts of interesting things to happen!

 

[JohnT]

The only time Ive ever had dirt/algae shoot back into the pool was when I turned most of the suction towards my skimmer, and the filter was freshly backwashed. My theory was that the clean filter wasnt providing enough back pressure and the dirt was literally just being pushed right thru the filter and back into the pool. Not sure if that theory is valid, but once the suction was split between main drain and skimmer the issue went away.

What kind of pressure readings are you seeing on the filter gauge?

Double check to make sure the pump and multiport are plumbed correctly........I made that mistake once, plumbed the pump output to the multiport OUTLET instead of INLET. That caused all sorts of interesting things to happen!

Plumbing is rigid PVC, so it can't move. Pressure was normal for the pool, 18psi on filter, jumping to 20psi with the solar on. When I changed the sand, the non-solar pressure dropped about 1psi.

The dirt doesn't come through when the filter is clean, but when it starts to get dirty, the dirt just suddenly blows through.

 

[chrisexv6]

Wow! Thats a weird one. I always thought mods were immune to weird pool issues

Everything I had in mind would have to do with the multiport but you already replaced it.

Its like the valve is somehow ending up in recirculate position, but again its a new valve so most likely thats not it.

Does the pressure change when the dirt starts getting returned into the pool?

 

[JohnT]

Wow! Thats a weird one. I always thought mods were immune to weird pool issues

Everything I had in mind would have to do with the multiport but you already replaced it.

Its like the valve is somehow ending up in recirculate position, but again its a new valve so most likely thats not it.

Does the pressure change when the dirt starts getting returned into the pool?

Believe me, I've sat out there with the multiport in my hands, staring at it for hours. It still seems impossible to me that it could be getting through the sand, so it makes me lean toward the multiport or the junction where the riser goes into the multiport. It seems that the slight pressure rise as the filter starts catching dirt causes the water to go through someplace it's not supposed to and bypass the filter.

 

[chrisexv6]

Did you remove the o-ring you had added to the riser/multiport connection? Could that somehow be interfering with the direction of the water flow?

I wonder if maybe the riser is "weak" and might be collapsing in on itself once there is enough pressure from dirty sand? Or even more of a stretch....if one of the laterals is somehow flipping vertical and shooting water straight thru the sand back up to the multiport....that would act like a channel, but if the lateral flips back down when you turn the pump off you might not see it (like I said, stretching )

 

[Bama Rambler]

Here's a wild idea. When the pressure rises the filter body expands vertically just a bit and causes the connection between the riser and the MP to open up a bit. It would happen slowly and you probably wouldn't notice it and if the riser is just long enough to engage the o-ring then I could see where this might happen.

I also remember many years ago we had an old outboard motor that would act up at times and after many trips to the mechanic I took the carbs apart and while cleaning the siphon tubes (think riser) with compressed air I found a hairline crack in both of them. You couldn't see it with the naked eye but replacing them solved our problem.

I'm just throwing out thoughts because it's such a special problem.

 

[JohnT]

Did you remove the o-ring you had added to the riser/multiport connection? Could that somehow be interfering with the direction of the water flow?

I wonder if maybe the riser is "weak" and might be collapsing in on itself once there is enough pressure from dirty sand? Or even more of a stretch....if one of the laterals is somehow flipping vertical and shooting water straight thru the sand back up to the multiport....that would act like a channel, but if the lateral flips back down when you turn the pump off you might not see it (like I said, stretching )

Here's a wild idea. When the pressure rises the filter body expands vertically just a bit and causes the connection between the riser and the MP to open up a bit. It would happen slowly and you probably wouldn't notice it and if the riser is just long enough to engage the o-ring then I could see where this might happen.

I also remember many years ago we had an old outboard motor that would act up at times and after many trips to the mechanic I took the carbs apart and while cleaning the siphon tubes (think riser) with compressed air I found a hairline crack in both of them. You couldn't see it with the naked eye but replacing them solved our problem.

I'm just throwing out thoughts because it's such a special problem.

It's back to normal with the extra O-ring and tape removed. The riser goes about 2" into the multiport valve body when it's installed.

The laterals on this filter don't fold, so they are locked in a horizontal position. Water flows into the laterals from the sand, except during backwashing, so that's not likely a problem.

Absolutely zero sand going to the pool, and I removed each lateral from the riser and looked at the whole works pretty carefully.

I've seen similar things where a small crack caused untold problems. Like an aluminum carburetor body that had a seam near a mounting screw. Only it wasn't a seam, it was a crack, and when the bike got hot it leaked air :x

I have tried to imagine where a crack could be located to cause such an issue. Clearly, the multiport was my first guess, and the second possibility that came to mind was a crack in the riser above the sand, or even near the top. Since I'm not getting any sand in the stockings over the returns, I think that tells me that the mixing of water is happening above the sand bed. I believe I checked the riser very closely, running my thumbnail over it to see if I could feel a crack. My next idea is to pull the multiport and wrap the riser with Gorilla tape from the sand to the point where the multiport sits. I wouldn't expect a permanent fix, but it should let me vacuum long enough to see if there is a difference.

Before, it wasn't such a big deal because it was early, but now we have 90 degree weather in the forecast, and I'm going to be under pressure to have the pool ready . My 3 year-old grandson was ready to swim in April, and if he can't swim on his birthday on the 31st like I promised him then, I'm going to be in deep trouble.

 

[chrisexv6]

Hate to say it....buy a new riser/lateral setup?

At that point if its not fixed you might need to call in someone to get rid of the gremlins!