Afraid to ask - Pentair FNS 48 with possibly wrong valve?

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bronsonj

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Oct 25, 2016
1
Saint Petersburg, FL
About 4 years ago (maybe more) I had a Pentair FNS 48 Plus installed at my rental house. Since I don't live there I don't know of issues unless someone complains and the renters appeared to love the DE filter vs the cartridge filter it had as I never heard complaints from them since.

Well, the renters are gone and I am fixing up the house.

I notice the FNS 48 never gets above 8 (or so) psi. I finally open it up and there is NO media on the grids or collected in the bottom of the filter housing. I know it had DE. Regardless, I was replacing all the internals of the filter since it had been so long and while I am there, may as well. I tried to remove the entire assembly (manifold and grids) but could not. So I took the manifold off and pulled the grids out one by one... The grids weighed about 30 pounds each! The DE media was INSIDE the grids! So I was looking all over the system and I notice the MPV says "for sand filters only".

My best guess is that the install guy put the wrong MPV on? But how has the filter worked so well? The pool is crystal clear!

I did not do the install, I paid a company to do this, and like most pool places they've closed down since so I can't ask them.
I am not a pool guy, but DE should be on the outside of the grids... Any advice is appreciated as my best guess is I have the wrong valve on there.
 
It's definitely the wrong valve and should be replaced. It should not be run as is.

It should work about the same either way as far as filtering.

Pentair 261152 Multiport Valve Kit 2in. Threaded is what you need.
 
thepoolman said:
You don't need a new valve. Those MPV will work for either sand or DE, but the key is rotated 180 degrees depending on the filter you have. All you need is the sticker for DE. See the item posted below.

https://www.poolpartsonline.com/p-52413.aspx?searchEngineName=label-high-flow-de-273207-opt-4623-21a&utm_source=google&utm_medium=ShoppingFeed&utm_term=ProductListingAds&utm_content=AllProducts&utm_campaign=GoogleShopping&gclid=CP6Srd7r-M8CFcRkhgodfecB-g
Click to expand...

Not interchangeable. The sand valve won't work on DE. There's only one position that goes to the bottom of the tank and that returns to waste. There is no position that will filter.

You could switch the waste and return lines to make it work. You would have all positions except rinse. You would have one position that backwashed to the return.

I would replace the valve.
 
JamesW said:
Not interchangeable. The sand valve won't work on DE. There's only one position that goes to the bottom of the tank and that returns to waste. There is no position that will filter.

You could switch the waste and return lines to make it work. You would have all positions except rinse. You would have one position that backwashed to the return.

I would replace the valve.
Click to expand...

The 261152 valve that you posted is literally the exact same as the 261152 sand valve. The difference is the sticker and the valve handle orientation. They are 180 degrees different from each other.

Bronsonj, can you post a picture of what is currently at the house?
 
Same parts except body.

180 is rinse, not filter. There is no position that will filter.

Take apart a de and sand valve and compare them position for position and you should see what I mean.
 

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You're still not getting it. For de, the big opening goes to the bottom union. For sand, the big opening goes to the top union.

The OP can easily verify what position is 180 from filter. Turn off pump, rotate valve 180, turn on pump. If 180 is filter, water will go to returns. If 180 is rinse, water will come out waste.

Put the diverter at each position to see what each will do. It should be obvious that it won't work.

What position would the diverter need to be in for "Filter"?
 
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thepoolman said:
Well I just posted a picture that proved me wrong and said I was eating crow. Nothing left for me to get.
Click to expand...
I thought it was a brief and humorous concession 'speech' :D Plus photo to help out future readers as well as the OP :goodjob:

I'm still trying to picture the flow path; i.e. how the filter apparently still functioned as a filter, but with the DE on the inside of the grids...!
 
singingpond said:
I thought it was a brief and humorous concession 'speech' :D Plus photo to help out future readers as well as the OP :goodjob:

I'm still trying to picture the flow path; i.e. how the filter apparently still functioned as a filter, but with the DE on the inside of the grids...!
Click to expand...


It is cool when you get to the root cause of a problem. THEN you know exactly how to fix it, and you can be sure it is fixed.
 
Flow path with sand multiport on filter:
In through the top multiport threaded hole labeled "pump", inside the multiport on top of the diverterer, through the diverter hole, through the top union, up the standpipe, inside the grids, through the fabric, outside the grids, through the bottom pipe back into the multiport, 180 degree turn under diverter, out of the multiport to the return line.

The de coats the inside of the fabric. The water still has to go through de and fabric, so it filters.

The main difference is that water usually goes from the outside of the grids to the inside, which pushes the fabric against the grids. In this case, the water goes from inside the grids to the outside, which causes the fabric to balloon out.
 
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