Removal Piston Assembly From Pac Fab 2″ PVC Backwash Valve

Removal Piston Assembly From Pac Fab 2″ PVC Backwash Valve

Most home pool systems have a backwash valve that allows the owner to send pool water through the filter, typically diatomaceous earth, to rather quickly and cheaply clean the filter.  I encountered a major problem with our backwash valve.  I could not make it function properly.  It would not slide the plastic handle completely down and thus I sent a small stream of water out of the pool when the pool pump was running.  When I tried to take the valve assembly apart, the piston refused to come out.  I followed the directions from the manufacturer but it would not budge.  This article is an addition to the instructions that come with the unit.  Please note that this process will require you to buy two new O rings.

Theory behind this repair. If you have not replaced the O rings within the past two years, there is an increased chance that the O rings will enlarge.  Over time the rings will enlarge so much that the valve can not function properly.  Swelled O rings will make removal of the valve impossible.  We will therefor attempt to remove the O rings so we can pull the plastic handle of the valve out and initiate a proper repair.


  1. You should already have released all pressure from the system and drained the filter of all water.
  2. Unscrew the two large plastic valve nuts that connect your filter to this backwash valve.  I found the Husky 8 inch strap wrench (SKU 181 364) to be perfect for this task.  This wrench is a bit tricky to use and there is no instructions as to how to use it.
  3. Once the two nuts are totally loose, backed away and unlocked from the filter unit, slide the filter unit out of the way so you can easily view inside the backwash valve.  You now should see two large openings.
  4. Use a hefty, thick wire, clothes hanger and form a C or J at one end using a pair of pliers.  We will use this wire to hook the O rings inside the valve.
  5. Position the valve about half way up and down so the plastic plates holding the O rings are centered in your view when looking into the openings of the valve.   You may need the use of a flash light to view what you are doing.
  6. Carefully slide the close hanger hook behind the O ring.  I snagged the O ring by sliding the coat hanger along the top of the O ring with the hook parallel with the ring and then twisted the hanger down and around so the hook came behind the rubber ring.
  7. Pull the ring out until it breaks or use some cutting tool.  I just pulled until the O rings broke.  You will need to do this through the top and bottom valve openings.  Make sure you remove both O rings from the valve.  You should end up with two broken O rings.
  8. The plastic valve handle should now easily be pulled completely up and out of the valve.

Follow directions as to replacement of the O rings in your manual.  Be certain you apply the silicone to the rings before assembly.

In my case, the O ring at the bottom opening was so swollen, that it stopped the piston from being withdrawn.  Once the O ring was cut, the piston was able to be pulled apart.

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