workshop ] how does it work ] History of Astronautics page index ] Rocket launches ] useful sites ] version francaise ] Contact us ]


PET Bottle explosion standard.






















Remote pressure test rig.

Dsc01615Pressure_test_stand_withBadoit_bottle.jpg (63393 bytes)

Safety is the first priority when pressure  

testing plastic bottles.

So we have developed a system that enables  

us to pressurise and remote control the test rig at a safe distance of 12m.

Please note that we have also developed our own detailed test 


This can only be carried out with adult supervision.


        Note: At least with the videos you get an idea what sort of energy 

                     level is involved.

What does PET stand for ?

A plastic material called polyethylene-terephthalate ("PET")..


When was the first plastic drinks bottle made ?

Patented by Nathaniel Wyeth (US) in 1973. First used in volume recycled production in 1977



Currently capable of testing at pressures in excess  of 25bar.

Compressed air is supplied from an electrically driven compressor, then stored in a small reservoir and the supply regulated using three regulator valves in conjunction with a pressure gauge.

Fine adjustment is obtained by using two fine vernier  needle type regulator valves that have in built one way valves .



Pressure testing of bottles should be carried out safely with the bottles filled with water.  This  reduces the explosion energy introduced by the compressed air as  it expands  back to atmospheric pressure.

This test was undertaken to determine the pressure at  which the bottle would fail in a launch condition. Without stiffening additions such as bonded fins or nose  module caps that locally increase the wall thickness of the bottle.





  • 1 Liter 'Badoit' pressure test failed at 19.5bar




Now imagine you could control this amount of energy  to launch a rocket.

Release of this energy in the form of a controlled jet with a high mass transfer or flow rate is what accelerates  and creates the jet thrust force in water rockets at launch.

This type of jet thrust force and acceleration is the same principle used to power real rockets. Like Ariane4 , Ariane5, Atlas ,Space Shuttle and Soyouz

  • Analysis of 'Badoit' debris

Dsc01628Analyse_badoit_explosiondebris.jpg (62559 bytes)


Health and safety standards.

      Compressed air over water propulsion systems (that  include water rockets and there derivatives). 

      Need to be treated with respect.

      The parameters that need to be controlled are:

  • Specification of launching system that controls the launch trajectory in a stable, consistent and predictable flight path.

  • Selection and security of the launch site.

  • Knowledge of the meteorological conditions and recognition of there affect on rocket trajectory. This consequently affects the selected position of spectators relative to the launch site.

  • Always keep spectators  and the flight team up wind so that the rocket travels away from them.

  • Where will the rocket land if the recovery system fails.

  • The rate of pressure increase and the accurate control of maximum pressure supplied to the rocket bottle.

  • Use of safety dump security valves. To release pressure safely. In case of emergency or system failure.

  • Utilisation of remote pressurisation and launch capability. Distance depends on launch pressure used.

  • We use a distance of 12m or 1m for each 1bar of pressure.

  • Criteria for the selection of a safe PET type bottle.

  • Define the maximum safe pressure Pmax.

          Listed below are just some of the parameters involved 

          so please be careful and beware of over simplifications. 

          Experience has confirmed that the selection of a good 

          quality bottle is the primary priority for controlling 

          safety. If you can quantify how the bottle will perform 

          Then you can define a safe operating window.

  • Control , record and restrict the total number of flights made by each rocket.

  • Analyse impact damage and reject anything you think might possibly affect either flight or launch capability. Be ruthless

  • Introduction of a set of manufacturing and launch check procedures to remove the chance of accidental error

    causing system failure. A continuing evolution of 

    procedures will both improve performance and safety.




      Pmax is proportional to : Pch Charging pressure in bar and several 

        other  parameters listed below.


       Pmax = C*Pch ( e, g,1/n,1/Ns, tp, te,1/Nc, dP/dt,  E, G ,r, K, dK, I )

  Quality of the bottle used. :    e    Homeogeinity of the PET wall thickness e.

                                                     g     Elasticity of the PET plastic material. 

                                                     n    Number and density of imperfections and 

                                                             molding marks. Stress raisers.

                                                     Ns  External damage due to scoring or impact.

                                                     tp    Onset of plastic deformation.

                                                     te    Start of wall thinning.

                                                     E    Young's Modulus for the material.

                                                     G    Shear modulus

                                                     r   Charge density  

                                                     K    Ambient absolute temperature.

                                                     dK  Thermal shock interior to exterior.

                                                     C    Proportionality constant.

                                                       I    Exposure time to strong UV light


Inversely proportional:  

                                        Nc The total Number of pressure cycles to which the 

                                               bottle has been exposed.


                                             Fatigue limit will be determined by the number 

                                             of pressure loading cycles to failure. At a specified

                                             pressure amplitude. 

                                             Reverse stress condition could occur if the 

                                             pressure  within the bottle expands below




                                            dP/dt The rate of pressure increase.


Note: All these parameters need to be arranged into dimensionless

          groups that can be  subsequently used to rate different types of bottle. 

          To provide sufficient data. Thorough testing of both the materials and  

          different types of bottles needs to be undertaken.

          This could then be used to generate a dynamic  behaviour model.


back ] menu of this section ] next ]


This site was created on the 15th April 2003


You're welcome to reproduce any material on this site for educational or other non commercial purposes

 as long as you give us proper credit

(by referring to "The Water-Rocket Explorer"