Problem installing/seating SM-20-3 spider gasket


LifeTime Supporter
Mar 10, 2008
Lafayette, LA
I installed a new spider about 3 weeks ago. It was for a 2" sidemount Triton SM 20-3 backflush valve. There were 2 to pick from at the LPS. I chose the one that had the larger diameter center hole, which matched my old gasket.
I cleaned all the mating surfaces super slick. I used ptfe lube to put it in. But whenever I finished installing it, the spring tensioned plunger would not depress. It was stuck in the up position, handle down and loose.
I took it back apart and flipped the gasket over, with the sealing ridges up. It fit a bit better but once again, the plunger couldn't depress correctly once everything was tightened back up. I had very carefully torqued the flange bolts, using a star pattern as I took it down in stages. I am very certain the gasket was not out of the groove when finished.
I thought that maybe the gasket was a bit thick so that it could compress with the spring tension over the next few days and take a seat. That never happened and when I went to backflush it the first time 3 weeks later, it tore. It was tight, but operable when I first installed it.
Where am I going wrong?
Is there a thinner gasket for a 2" side mount SM-20-3 valve?
Thanks, Shell


LifeTime Supporter
Feb 8, 2009
New Jersey shore
i know this is old, but i think the problem is the valve itself and not the gasket. I would replace the top haf of the muliport valve. Also, anytime you are installing a new gasket, it should be super glued into the track, otherwise it will pop out everytime you go to backwash.

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