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.
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
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:
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.
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
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
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.
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" http://waterocket.explorer.free.fr).