Cracked 4 manifolds on FNS plus 36

[Reiter284]

I have cracked 4 manifolds on my FNS plus 36 DE filter. One on the top by the bleeder and 3 on the bottom where the seam is molded.

This has happened over the course of about 4 years each one spaced out about the same.

I have a 1.5hp pump and all 2” fittings. Each time it’s happened my pressure is running at the “clean” level.

Are these manifolds that fragile? Should I upsize my filter? Should I never allow the pressure to get that high? I also saw there is a heavy duty one on amazon.

Any input is welcome. I’m contemplating buying a FNS Plus 60 or purchasing the HD manifold.

 

[mknauss]

Welcome back to the forum!

I do not have a DE filter but let's see if others with one can give you some advice. @jblizzle @Richard320 have DE filters.

 

[jblizzle]

Never had that problem on my Hayward DE filters, but not sure if the Pentair is more delicate.

Are you over tightening not that holds the manifold to the top of the grids? It would be very surprising that the pump has anything to do with the issues you are having.

 

[Oly]

How many psi in your filter system?
On a related note the new variable speed pumps have a slower and gradual startup to reach operating pressure. My old single speed pump would hammer my system on startup. You can also set your rpm on a vs pump to lower your operating psi.

 

[TBSNPS]

I have a FNSP-48, I am led to believe the manifold is the same as yours, the height of the filters differs. My research indicated that Pentair has a problem with manifolds cracking. On the side of my filter there is a plackard that indicates to backflush when pressure rises 10 psi over "clean" pressure. That differs from the recommendations here on this site. I've repaired my manifold with SS safety wire and an adhesive I got at the local "plastic store, TAP Plastics". I brought the manifold in to them and they tested a few products to make sure they sold me the correct adhesive. Imagine that !!
My "clean" pressure is 10 psi, I backwash at 13 psi per this site recommendations, NOT the 10 psi over as recommended by Pentair. I've not had a problem since adopting this approach.
While looking for an Aftermarket manifold on Amazon I was reading all the reviews and this exposed the problem with cracking manifolds, mostly around the bleeder tube on the top side. There is one Aftermarket manifold on Amazon for around $60 that gets good reviews. Thats about 1/2 the cost of Pentairs weak puppy.
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