Fire Piston Instructions

My fire piston does require a bit of technique hopefully this video should give you a general idea

So:

  • Check the tube for damage, it is polycarbonate so should be very tough, but any cracking is a bad sign
  • Make sure the o-rings are well lubricated with vaseline particularly the piston - though if you put it on with a spade, I think it can make it harder to ignite. Basically enough that the piston moves smoothly all along the tube.
  • You don't want to do it on a slippery floor, I normally carry a 40x30cm square of carpet which stops it slipping while the gas is compressed - otherwise you get an impressive pop and a high velocity bung.
  • Put a little bit of teased out cotton wool into one end.
  • Depending on your weight, put the bung in, and then push the piston in a quarter to a third of the way down, or vice versa.
  • Hold it to your stomach near to your pelvis, try to get the piston as vertical as possible so you are not applying any sideways forces.
  • Then drop onto it by bending your legs, it is quite difficult to persuade your hindbrain to do this, but the tube is strong enough for me so it should be fine for most other people.
  • Even if it fails to ignite, it has probably fizzled, and filled the tube with CO2 so open the tube right up, waft it around a bit, and start again.
  • You will probably find it easier to remove the bung immediately after the compression as the gas between the o-rings is normally hot then. I think it sometimes cools, shrinks and pulls the tube inwards, jamming the bung in the tube.
  • Don't use anything more flammable than cotton wool, definitely nothing explosive (there is, I believe, a story, but nothing to do with me).

If you are still having difficulty making it go there are two tricks that reduce the pressure in the tube:

  • Push the piston 1/3 of the way in then add the cotton wool and the bung, this means the tube isn't already slightly compressed so you don't have to push so hard to compress it the 7-10 times to make it ignite
  • If this doesn't work push the piston 1/2 or 2/3 of the way in, then add the cotton wool and bung, now pull the piston back out to only 1/3 of the way in, wait for the air to warm up for 3-40seconds then compress it. This means you are starting off below atmospheric pressure so the air pressure will help you, to start with and the maximum pressure is even lower.

If you want to know more about how it works, I wrote the fire piston up as a kitchen science

My risk assesment

 

Experiment Hazard Risks to Audience Risks to Presenter Control measures Residual risks to audience Residual risks to presenter
Fire Piston – igniting cotton wool using pressure, in a sealed transparent tube Tube failing Being hit by pieces of shattered tube Being hit by very fast moving pieces of tube Tube made of poly carbonate which is very tough and doesn't fail by shattering. Base of tube is not held flat so there are minimal twisting forces on tube so failure is less likely. - Failure of tube leading to presenter falling over.
  Force needed to generate ignition is large - Injury to back Presenter should be comfortable using the equipment as instructed – in practise this means extensive rehearsal - Small
  Base of tube slipping, and end stop coming off and flying across the floor Low chance of being hit by end stop of tube. - Either the audience shouldn't be sitting on the floor or there should be a low barrier between them and experiment. Do on a piece of carpet so it is less likely to slip. very low chance of minor bruise to shin -
Sales pitch: 
The fire piston is a fairly simple device, essentially you compress air until it is hot enough to ignite some cotton wool.