I just replaced the backup valve on my Polaris 3900. The old one did not function and the cleaner would spend a lot of time stuck at the steps or shells. The new on works properly and what a difference in performance. Apparently the mechanism in the old unit was stuck and was restricting the water flow.
FYI
There was green alge in the threads of the nuts that attach the hoses to the reverse valve. That stuff will hide anywhere.
FYI
There was green alge in the threads of the nuts that attach the hoses to the reverse valve. That stuff will hide anywhere.