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Water Rocket Pad Fill Accessory.

by Mike Passerotti

The idea is to pressurize a water jug and provide an outlet for the water.  The trick is to pump air into the top of the water jug and prevent air from entering the water line.

Parts List:






Water Bottle

5 Gal.



Grocery Store



22 1/2" Length


Hardware Store

Sched 40 PVC


6" Length


Hardware Store

Sched 40 PVC Slip "T" Connector




Hardware Store

Sched 40 PVC Slip Cap




Hardware Store

Hose Clamp




Hardware Store

Garden Hose


48" Length



Male Garden Hose End Repair Part




Hardware Store

PVC Cement

small can


$1.49 can

Hardware Store

PL Premium

Caulking Tube


$3.95 tube

Hardware Store

Automotive Tire Valve Stem (All rubber)

.453" Opening



Auto Parts Store

Bailing Wire or electrical wire

3 or 4" piece




Tools Requirement:

PVC Pipe Cutter, Drill, 5/8" Drill Bit, 1/2" Drill Bit, Flat File, Screw Driver, Knife (Or something suitable to cut a garden hose.)

Parts Preparation:

1/2" Sched 40 PVC:

A.  Cut 1 piece 2" long.

B.  Ream about 3 inches of PVC with the 5/8" drill bit.

C.  Test the reamed PVC to make sure it slips over the CPVC without major stress.

D.  Cut 2 pieces 1" long, 1 piece 1/2" long of the reamed PVC section.

E.  Clean all parts.  Using the flat file, cut the lip off the ends so the parts will easily slip into the couplings and over the CPVC.

pad_fill_construction_lip.gif (1304 bytes)

F.  With the flat file, notch the inside of one 1" piece and the 1/2" piece.  Cut about halfway through the wall of the PVC.

pad_fill_construction_sched40.gif (5083 bytes)

1/2" CPVC:

Cut 1 piece 22 1/2" or slightly longer if desired.  With the flat file, cut the lip off the ends so that the 1/2" Sched 40 will slip over the ends.

1/2" PVC Slip Cap:

Drill a 1/2" hole in the end of the cap.  Insert the tire valve stem with the threaded cap end on the outside.

pad_fill_construction_cap.gif (2345 bytes)

Water Bottle Cap:

Take the cap off the water bottle.  Drill a 5/8" hole in the center.   With the flat file, notch one side of the hole in the cap to match the notch in the PVC.

pad_fill_construction_bttl_cap.gif (2026 bytes)

Water Hose:

Cut about a length of hose (preferably an old hose) any length that is usable for your launch pad.  About 3 to 4 ft length is required to come off the top of the bottle, snake down to the hose hookup and give a little slack to move the bottle out of the way during launches.


Assembly should be done outside, with old clothes on because the PVC cement and PL Premium are hazardous to work with.  Make sure the assembly area is uncluttered and you have clean up rags or towels handy. Test fit pieces before gluing.

1.  Mark the CPVC 18 1/2" from one end (or the depth of the water bottle).  This line is where the water bottle cap will go.  Slide the 1/2" Sched 40 notched piece onto the CPVC and glue in place on the inside of the mark.  When gluing, don't put glue on the notch.   The notch must remain open for air to pass.

pad_fill_construction_assm1.gif (3454 bytes)

2.  Slip the water bottle cap over the CPVC short end.

pad_fill_construction_assm2.gif (3971 bytes)

3.  Slip the notched 1" length of Sched 40 PVC over the short end and glue in place.  Immediately after pushing together the assembly, use the section of wire to help align the notches and open the air passage.  Remove the wire. Do not disturb the alignment until the glue sets.

4. Glue the PVC "T" connector over the 1" Sched 40 piece. Be careful not to plug the air passage. You can run the wire through the hole again if glue gets into it.

5. Glue the second 1" length of PVC over the CPVC and inside the "T" coupling.

6. Glue the 2" length of PVC into the perpendicular port of the "T" coupling.

7. Glue the PVC cap with valve stem over the 2" piece of PVC.

8. Spread PL Premium around the joint where the water jug cap meets the 1/2" Sched 40 PVC. Let the PL Premium dry at least one day. Two day drying time would be better.

9. Slide the hose clamp over the end of the garden hose. Push the garden hose end over the CPVC above the "T". Clamp down the hose real tight. Add the garden hose repair end to the other end of the hose.

Final Assembly: Put water in the water jug, screw the cap assembly on and its ready to use.


Warning: The cap will not take much pressure. 40psi is good. The cap is fragile so take care handling the setup. Do not lift the bottle with water in it by the pipes on top.

Connect the garden hose to the launch pad. Close the water valve on the launch pad. Pump up the water jug with a reasonable pressure (about 40 psi).

(First time only) Open the valve on the launch pad to bleed the air out of the line. Close the launch pad valve. Repressurize the water jug. Place a rocket on the pad.

Open the water valve to fill the rocket to the desired level. Close the water valve.

If the water level is below the top of the launch tube, then bleed off the water in the launch tube. You can bleed the water out by the air valve on the launch pad. The air going into the pad will add more water (undesirable for controlling the water level) to the launch pad as it bubbles over the top of the launch tube. When adding water to the bottle, the bottle will have some pressure which can be used to bleed off the extra water. Launch the rocket.

When finished launching, make sure you bleed the pressure off of the water bottle before disconnecting the garden hose.

Optional usage: Put a garden hose nozzle on the end of the garden hose and fill rockets off of the pad in a controlled way.

Optional usage: Put a garden hose nozzle on the end of the garden hose and soak the nearest person.

Feedback welcomed.

Note: I'm currently working on a pad fill rig that uses 2 liter bottles all connected together in a manifold. Stay tuned.