Can a bad multiport valve allow filter sand back into the pool?

SinistrV6

Well-known member
Sep 6, 2008
138
Mississippi
I've chased this issue for a while now. Replaced laterals/standpipe with no change. Had all pool lines pressure and vacuum tested (all passed). Can the valve itself allow sand back into the pool? It's original to the build (about 14 years ago). Appears to work properly otherwise. It's definitely sand (you can feel it with your fingers) and it's a significant amount. Robot is picking it up too.
 

Rocco

Well-known member
Dec 23, 2012
269
Manassas Park, VA
Yes it can. There is a gasket (normally referred to as a spider gasket) in the multi-port valve that can go bad.
I have had to replace it a couple times over the last 11 seasons.

It is recommend to only turn your valve in one direction (clockwise or counter clockwise) even if you just need to go back one setting.
 
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HermanTX

Gold Supporter
May 20, 2020
2,779
Katy TX
Pool Size
14600
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Chlorine
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The spider gasket can tear over time and allow communication between ports. However, is the sand coming out of the return jets to the pool? Have you tried to capture any sand from the jets? You can put the multiport valve in Circulate position. This bypasses the flow through the sand filter and determine if you have any sand particles.
 

SinistrV6

Well-known member
Sep 6, 2008
138
Mississippi
The spider gasket can tear over time and allow communication between ports. However, is the sand coming out of the return jets to the pool? Have you tried to capture any sand from the jets? You can put the multiport valve in Circulate position. This bypasses the flow through the sand filter and determine if you have any sand particles.
I have not tried that but I will. Pool was completely clean from new liner install. Over the next 6-8 weeks it built a good amount of sand all over the pool. Once I get it cleaned up, I'll put it in Circulate to see if it returns. Of course, if the valve is malfunctioning, that may not be a clear determination.
 

JamesW

TFP Expert
Mar 2, 2011
28,291
Is that sand on the steps?

Get a knee-hi stocking and use a rubber band to secure it to a fitting that you can screw into the wall return.

Periodically, check the knee-hi for sand to confirm that the sand is definitely coming from the returns.
 

SinistrV6

Well-known member
Sep 6, 2008
138
Mississippi
Is that sand on the steps?

Get a knee-hi stocking and use a rubber band to secure it to a fitting that you can screw into the wall return.

Periodically, check the knee-hi for sand to confirm that the sand is definitely coming from the returns.
It is. The robot is full of sand too. I have no doubt what it is and the sand filtration system is the only available source.
 

JamesW

TFP Expert
Mar 2, 2011
28,291
How is the sand getting on the steps if there are no step returns?

Sand is heavy and dense and it sinks pretty fast, so if it is coming out of the returns, most should be piling up near the returns.

I would do the knee-hi on the returns just to be 100% sure.
 

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JamesW

TFP Expert
Mar 2, 2011
28,291
If it is definitely filter sand, it pretty much has to be an issue with the laterals or standpipe or the sand is too small.

Different sand has different sizes. Some sand has mixed sizes and the smaller particles can go through the laterals.

If the sand if definitely coming from the returns, then reexamine the laterals and maybe go to a larger size sand.

The multiport can’t cause the issue unless the multiport was plumbed incorrectly and the water was going backwards.


 

SinistrV6

Well-known member
Sep 6, 2008
138
Mississippi
If it is definitely filter sand, it pretty much has to be an issue with the laterals or standpipe or the sand is too small.

Different sand has different sizes. Some sand has mixed sizes and the smaller particles can go through the laterals.

If the sand if definitely coming from the returns, then reexamine the laterals and maybe go to a larger size sand.

The multiport can’t cause the issue unless the multiport was plumbed incorrectly and the water was going backwards.


That's why I asked about the valve. I never really considered the size of the sand. Just bought what the pool store had in stock.
 

JamesW

TFP Expert
Mar 2, 2011
28,291
Swimming Pool Sand filters generally use #20 silica sand which is approximately .40 to .55 mm.

If the slits in the laterals are a little bit large and the sand is a little bit small, then you can get some sand passing through the laterals.

MYSTIC WHITE II filter sand has three effective sizes, .49 mm, .65 mm or .80 mm.

MYSTIC WHITE® II .49

MYSTIC WHITE® II .65

MYSTIC WHITE® II .80



Maybe get some of the size 80 for the bottom sand near the laterals and then switch to 65 for the middle layer and 49 for the top layer.

 
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JamesW

TFP Expert
Mar 2, 2011
28,291
Put a knee-hi on each return to catch the sand coming out of the returns.

Give it a day to see what builds up.

Maybe the sand is too fine.

Try the 80 sand near the laterals and then the 65 and then the 49 on top.

How many pounds of sand does your filter take?
 

ferretbone

In The Industry
May 24, 2016
166
tx
Thats about 450 maybe 500lbs of sand. And James is right that looks like the wrong sand. It looks like play sand. I hate those top mount filters. Make sure that is the same color sand in your filter. Scoop some sand out of the filter and compare the two.

If that sand is on the steps it sounds like its not blowing from your jets. I know James said that already. Screen some jets to find out.

I see your home is under some kind of constuction
We drained a pool once and repaved the deck. We refilled the pool but had sand blow back for months. Nothing wrong with the filter. Turns out some sand and dirt washed down the drain pipe from the deck then hardend, and blew small amounts of sand into the pool.

Also dont ask me how but when construction pops up across the street, I get lots of dirt and sometimes sand in a pool from the wind.
 
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