PROJECTS: BOOM STICK
2c. Fit two 2" O-rings onto each end
of the main piece of the sanded insert
coupling. Then test-assemble the
entire piston. Using the other 2 pieces
of the insert coupling and two 1¾"
O-rings, enclose the 1" Schedule 80
PVC segment and the piston valve
assembly as shown.
NOTE: Pipe fittings are
tapered, which makes it
harder to get the parts to
fit together nicely when
they’re cut. Use epoxy
putty or gel to reinforce the
construction as needed.
2d. Use PVC glue or epoxy to glue the piston together. First, glue
the ¾" Schedule 80 segment into the 2" ring, on the side opposite
the bevel. Place a small O-ring as a spacer on the segment, and
glue this subassembly into the body of the insert coupler.
2e. Glue the piston valve halfway into the assembly, with the
neoprene washer facing in. Then glue the remaining insert
coupler piece around the outside half, with another small O-ring
spacer in between. Reinforce the connections with epoxy.
3. FIT THE O-RINGS
The large O-rings are bumpers that protect the PVC during operation. The small O-rings form the piston’s
seal inside the piston carrier and boom valve cylinders. The long end of the piston must mate with the
2"× 8" pipe, and the short end with the 2"× 6" pipe. The goal is for the piston to be able to fit into the pipe
and seal via the O-rings. These can be tricky to get right. With the PVC parts I bought, the perfect-sized
small O-ring would be t" thick. But I only found them available in 1" and 6", so I used the 1" size and
pushed them out with a layer of silicone caulk underneath.
3a. Glue flowed onto the small O-rings
in previous steps. This isn’t good for
them, so once the glue dries, cut or
pry them off and discard. Replace
with the remaining 2 small O-rings.
3b. Glue the large O-ring bumper pairs
together with silicone caulk. This keeps
them from jumping off. (You can also
try one thicker O-ring on each side.)
3c. Out of a popsicle stick, make a
small tool that fits a groove 1" deep
and 1" wide. Fill the piston grooves
with silicone caulk, and use the tool
to remove all but the thin layer that
it can’t reach. This will help the small
O-rings make a seal.
NOTE: You may need to
do this several times
before the O-ring seals
and the piston slides.
Even with everything fitting and well greased,
the difference between
success and jamming
or leaking is subtle.
120 Make: Volume 13