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Pump Construction

Written by Drenchenator
Last updated on 2007-12-20


Pumps in separate chamber water guns do one thing: move water from a reservoir to the pressure chambers. This action powers the gun. The quality of the pump determines the success of a homemade water gun. I tend to choose quality, which is why I designed this style of pump.

This guide does not show or tell a builder where or how to attach the check valves. These are vital to build pressure and are discussed in the article Separate Chamber Design. This design creates a pump with about a 12 inch stroke. The stroke can vary though based on the needs of the new design though.


  • 1" schedule 40 PVC
  • 1/2" schedule 40 PVC
  • 1/2" CPVC
  • 1/2" schedule 40 PVC endcap
  • 1/2" ID 5/8" OD O-rings (3)
  • 1/2" wooden or aluminum dowel
  • Epoxy
  • Bolts and Nuts


  1. Cut two pieces of 1/4" lengths of 1/2" CPVC pipe, and cut 15.5" of 1/2" wooden dowel. Cut 4.5" of 1" Schedule 40 PVC pipe. Gather 3 1/2" ID 5/8" OD O-rings.
  2. With a pair of scissors, cut both of the CPVC pieces on one side to allow them to be slid over the dowel.
  3. Arrange the CPVC pieces on one end of the dowel, allowing 1/4" between them for the O-rings.
  4. Glue the pieces down to the end of the dowel. Let sit for the time recommended by the gun.
  5. Drill a 1/2" hole in an unthreaded 1/2" Schedule 40 PVC end cap.
  6. After the glue has set and the O-ring mounts are secure, sand them until they are about 1/16 of an inch thick (or until them can easily fit inside of 1/2" PVC). Sand the middle area where the O-rings will go as well, because this will give the O-rings more room.
  7. Place the O-rings in the mount, and put the end cap over the dowel.
  8. Drill two holes on the end of the dowel opposite to the O-ring mounts. Drill one 1" from the end and another 1.5" from that one.
  9. Drill two holes in the 1" PVC section, one one in from one end and another 1.5" from the other.
  10. Using spacers or washers (as well as nuts and bolts), make a handle from the 1" PVC and attach it firmly to the dowel. Cut off extra lengths of the bolts as needed. File the ends smooth.
  11. Insert pump rod into the pump shaft of the gun.


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