Internal Air Bleed Assembly Pentair FNS Plus DE Filter

[bonedfredrik]

Hi everyone,

I have a question about the internal air bleed assembly on Pentair FNS Plus DE filters. Does it typically look like the one in my attached image? Most photos I’ve found online show this part with a mesh or “sock” attached, but I did find at least one example that matches the appearance of mine (Model #59023600, SKU #55-59023600).

Thank you for your advice.

 

[ajw22]

@1poolman1 @Lake Placid what have you seen in FNS filters?

 

[Lake Placid]

Majority I’ve seen look like 59023600 - 190092. I’ve seen a couple that look like 59011100 which is designed for the Titan filter. But who knows who touched those filters before I got there. Are you having an issue with it?

 

[bonedfredrik]

Majority I’ve seen look like 59023600 - 190092. I’ve seen a couple that look like 59011100 which is designed for the Titan filter. But who knows who touched those filters before I got there. Are you having an issue with it?

Thank you both for your help @ajw22 & @Lake Placid!

Since moving into our house a year ago, I’ve been struggling with a constantly rising pH in the pool/spa. A few days ago, I closed the spa return valve to stop the spillover in Pool Mode, hoping to reduce aeration. The valve likely hadn’t been adjusted in years. At first, everything seemed fine. I set the filter pump to run at low RPM (1250 and 1550) for 14 hours daily and at a higher RPM (2800) for 1 hour with the spillover on. The first night, the pump ran at 1250 RPM from 9pm to 5am. The next morning at 8am, I found a large amount of DE powder in the pool, mostly settled in the deep end. I’m not sure if it entered the pool while the pump was running or after it turned off.

To investigate, I cleaned and inspected the filter for any tears or cracks, then reopened the spa return valve and added fresh DE powder. With the spa return valve fully open and the spillover running, there have been no further issues for two days. No DE is leaking back into the pool, regardless of whether the pump is on or off.

mknuass gave me some great advice in another thread, however I still haven’t found an explanation for why the DE leaked into the pool. As far as I understand, the spa return valve shouldn’t affect this issue, but after what happened, I’m hesitant to adjust it again.

I’m not sure if the air bleed is related to the issue, but it looked unusual to me compared to other examples of that part I found online.

I appreciate any additional input you may have!

 

[Lake Placid]

As long as the air bleed tube fits tight, and it has a strainer of sorts on it that is not torn, the it’s not your issue. If you inspected the grids, and you had no tears in the fabric, and the plastic frames aren’t breaking down, that would rule out DE entering through the grids. Other causes of DE entering - the standpipe on those filters should have an o-ring in a groove on the top of the standpipe. It’s where the grid assembly inserts on to. If it’s missing, it can allow DE back into the pool. Next suspect would be a failing multi port. If those are all intact, it coukd be the grid assembly wasn’t fully seated allowing DE to enter. You may have corrected that when you inspected and reassembled.

I’ve been struggling with a constantly rising pH in the pool/spa.

What’s your TA?…..you’re also on the right track with reducing spillover runtime.

 

[bonedfredrik]

Thank you for taking the time to respond! @Lake Placid

As long as the air bleed tube fits tight, and it has a strainer of sorts on it that is not torn, the it’s not your issue.
I was definitely confused about this because my air bleed tube appears to be just a solid piece of plastic without any kind of strainer.

If you inspected the grids, and you had no tears in the fabric, and the plastic frames aren’t breaking down, that would rule out DE entering through the grids.
Confirmed. There are no tears in the fabric, and the plastic frames are in good condition.

Other causes of DE entering - the standpipe on those filters should have an o-ring in a groove on the top of the standpipe. It’s where the grid assembly inserts on to. If it’s missing, it can allow DE back into the pool.
I can confirm that the o-ring is not missing on the standpipe. However, I found it difficult to get the filter manifold assembly to line up perfectly with the standpipe. However, in the end, I believe I got it to line up well.

Next suspect would be a failing multi port.
Got it. Perhaps this is what I should look into next. How would you go about inspecting the condition of this part? My pool system appears to have a "push pull slide valve" rather than an MPV.

If those are all intact, it coukd be the grid assembly wasn’t fully seated allowing DE to enter. You may have corrected that when you inspected and reassembled.
That makes sense. I disassembled and cleaned the filter assembly about a month ago, and it has been working properly since then, but it’s possible something wasn't fully seated. Could running the filter pump at a low rpm (1250) for several hours have caused a condition for DE to leak out that was not present at higher rpms?

What’s your TA?…..you’re also on the right track with reducing spillover runtime.
I've been keeping TA at around 50 since it seems to be easiest to keep the Ph in order that way. I've tried bumping TA up to around 80, but that requires me to use much more MA to keep Ph in check.

In summary, because the problem with DE leaking into the pool started right after I closed the spa spillover valve, I'm really hesitant to close that valve again. However, it would be nice to stop the constant spillover since I figure it would make TA and Ph easier to manage. If it was your pool, would you close the spa spillover valve again and see if the leaking DE issue continues, or would you approach it differently?

 

[Lake Placid]

Got it. Perhaps this is what I should look into next. How would you go about inspecting the condition of this part? My pool system appears to have a "push pull slide valve" rather than an MPV.

If you’ve got a push pull valve, that’s likely not your suspect. If it was failing you’d more than likely see water coming out the backwash port in filter mode.

Could running the filter pump at a low rpm (1250) for several hours have caused a condition for DE to leak out that was not present at higher rpms?

No. It would be the opposite. Higher RPM increasing the filter pressure would be more likely to cause DE returning to the pool.

I've been keeping TA at around 50 since it seems to be easiest to keep the Ph in order that way. I've tried bumping TA up to around 80, but that requires me to use much more MA to keep Ph in check.

That’s right. Maintaining you TA between 50 and 60 will prevent the PH from rising so fast.

If it was your pool, would you close the spa spillover valve again and see if the leaking DE issue continues, or would you approach it differently?

I would. See if DE re-enters. I suspect the grid assembly wasn’t fully seated, as stopping the spillover shouldn’t be a contributing factor.