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How LPG gas works


  • LPG evaporates under ordinary temperature and pressure; hence it is kept in pressurised steel bottles.
  • When an appliance is turned on, the liquid is dispersed and changed to vapour by the outside temperature.
  • The proportion of vaporised gas to liquid gas can differ dramatically in accordance with composition, and conditions of temperature and pressure.

How gas comes from a cylinder

  • LPG is stored in a cylinder, in a liquid state. In order to work it must undergo a phase change (vaporisation) from liquid to vapour.
  • When drawing off gas vapour, the LPG liquid boils to restore the lost pressure.
  • Propane boils at -42C. Butane boils at 0 degrees. At 0 degrees Butane vaporisation is very poor.
  • "Latent Heat" is surrendered by the LPG liquid during boiling (as the gas boils creating vapour) causing the temperature of the liquid to drop further.
  • The LPG's heat loss is replaced from the ambient air-surrounding the LPG cylinder via metal of the tank.
  • The rate of vaporisation is dependent on the temperature of the liquid and the amount of "wetted surface".
  • When appliance demand rises, the cylinder pressure drops.
  • As the appliance demand reduces, the cylinder recovers.
  • If demand is too high the cylinder will not recover and cylinder pressure will drop until the appliances stop functioning.

Tank size and fill level

  • Bottles are filled to 80 to 85 percent. LPG expands in heat so room is left for the liquefied gas to expand