Safety Instructions

By Marimo Labs - Updated 20 May 2024

Disclaimer

This water rocket launcher design is made freely available to promote learning in science and engineering. No warranty or guarantees are made regarding the safety, performance, or completeness of any designs, models, instructions, or analyses presented. Any kits sold or distributed by Marimo Laboratories LLC or its affiliates are made available for convenience and are not warranted for suitability for a particular purpose. Your use of these parts, models, or instructions indicate your acceptance of all liability that may result from their use and an agreement to hold harmless Marimo Laboratories LLC and its owners, employees, and affiliates.

Safety Instructions

Note that this launcher design is experimental and is not a toy.

Pressurized systems are inherently dangerous. Adult supervision is always required. 

Read and understand all instructions and keep a copy for reference.

A responsible adult must make a determination of whether your particular combination of printed and non-printed parts, ground anchoring systems, bottles, hoses, pressurizing systems, personal protective equipment, protocols, users, and environment are safe for your application. This adult has final responsibility for safety.

The launcher must be firmly anchored to the ground for use. Never point at anyone or anything. No one should ever have any body parts above a pressurized bottle, as the bottle may disengage unexpectedly at any time and cause injury. 

Bottle Selection Safety

Only PET (polyethylene terephthalate) bottles rated for pressurized beverages (soda/seltzer) should be used. To maintain a safety margin, bottles should not be pressurized past 60 psi/4 bar. Inspect bottles before every use and retire if damaged.

For routine use, pressurize to 30psi, particularly if children are participating. While the design has been stress-tested to higher pressures, the risk of injury rises significantly with higher pressures. 

Launch Site Setup

Before every use, all parts of the launcher should be inspected for breakage, deformation, and signs of excessive wear. If found, the launcher should not be used and should be disposed of properly. 

Find a launch site in a large grassy field, clear of obstructions such as trees, buildings, or power lines.

At the launch site, confirm that the launcher’s Legs are fully inserted into the Base. Confirm the proper orientation of the Collar and elastic bands relative to the Pin markings. 

Confirm the entire launcher is firmly anchored to the ground with the Base’s “PIN” arrow pointed away from the planned location of the person pulling the Launch Cord. If the supplied Pegs do not securely hold the launcher to the ground, you must supply your own anchoring. Confirm the Launch Cord is securely tied to the Launch Pin. A length of at least 10ft/3m should be used. 

Confirm that the Launch Pin slides out easily with a gentle tug of the Launch Cord without moving the launcher. A launcher tip-over is dangerous and may result in uncontrolled launch and injury. 

Avoid high temperatures and prolonged direct sunlight, as this may cause softening of the plastic and deformation, particularly if you printed your own launcher from PLA. (Launchers printed in PETG have higher temperature resistance, but precautions should still be taken to prevent overheating.)

Appoint a responsible adult as the Range Safety Officer, who has the duty to ensure safety in the launch area.

Prior to each launch

Before placing the water rocket + Core in the launcher, confirm that the launcher remains firmly anchored to the ground. Ensure that the site is clear for 100ft/30m in all directions and that there are no overhead obstructions.

Place the water rocket + core in the launcher. Raise the Collar and check Clamp alignment to ensure that all six Clamps securely hold the flange of the bottle when the Collar is raised. Insert the Launch Pin following the arrow on the Base. Confirm that the bottle is firmly held. The Launch Cord should be gently extended toward the planned location of the person who will pull the Cord. Ensure that the Cord is extended straight from the Launch Pin so the pin will be pulled out straight and not at an angle. No one should touch this Cord again until the rocket is ready to be launched.

Connect the pressurization system, which here will be assumed to be a standing manual bicycle pump. An extension hose should be used so the person pumping is at least 10ft/3m away from the launcher.

Launch protocol

Clear the launch area. No one should lean over the rocket and it must be assumed that it may release unexpectedly once pressurization begins. If anyone needs to approach the launcher, they should do so keeping as low to the ground as possible. No person should be closer to the launcher than the person pressurizing. 

Start pressurizing. If this is done by children below age 14, they should be accompanied by a responsible adult to stabilize the pump, monitor the pressurization, and ensure there is no tension on the pressurizing hose. The person who will pull the Launch Cord should stay back until pressurization is completed. If this person is a child below age 14, the child should be accompanied by a responsible adult.

The bottle may shift and rise slightly as pressure increases. If a problem is detected, stop pressurizing, release the pressure, and correct the problem.

Once pressurization is completed, the pumping device should be laid flat on the ground without pulling on the launch hose. The person pulling the Cord may now approach the free end of the Launch Cord, but should not touch the Cord until the Range Safety Officer gives the all-clear.

The Range Safety Officer should announce the launch and ensure that the launch area is secure. The all-clear can be given for a countdown.
The person pulling the Cord should take the free end of the Cord without putting tension on it. At the end of the countdown, the Cord should be pulled smoothly just enough to extract the Launch Pin. 3-2-1 Launch!

If the rocket does not launch, depressurize the launcher and bottle before troubleshooting. No one should approach the launcher until it is depressurized.

Depressurization/Launch Abort

To depressurize, ideally use a pressure-relief valve if available. Otherwise, disconnect the pressure hose at the farthest possible location away from the launcher.

Prolonged Storage

Before storing for a prolonged period, remove all tension and strain from the launcher by removing elastic bands and disassembling the launcher and Core. Allow all parts to dry. Store indoors. Avoid extremes of temperature and direct sunlight as this can lead to weakening and deformation.