Hi Sandy, my Maccsteam gas tank certificate shows an hydraulic test pressure of 300psi. At what temperature does propane/ butane mix vapour pressure become problematic? At what pressure do Ronson type filling valves vent? I'm pretty sure I've seen small gas tanks fitted with 5mm sight glasses.
It's always puzzled me why liquid gas vents from the filling valve when tank is full as there must be gas at the top of the tank.
Jerry.
Hi Jerry,
The test pressures for LPG tanks are calculated from the maximum possible vapour pressure achievable under conceivable storage conditions at a specific temperature.
In the UK this is specified as 35deg C (shade temperature).
A safety factor of x 1.9 is applied which results in the following test pressures: -
Butane (100%) = 14.5bar (211psi)
60/40 Butane/Propane = 26bar (375psi)
70/30 Butane/Propane = 23bar (330psi)
All UK manufacturers are required by law to apply the appropriate test pressure for the specific gasses their refillable tanks are designed for.
I believe the rest of Europe also apply these same test pressures in order to be compliant for export/import between member countries.
Other countries of the world will vary depending on climate and regional legislation.
With a test pressure of 300psi your gas tank is more than capable for Pure Butane but falls a little short for 70/30 Butane/Propane mix if full compliance is required where you use it.
Gas vapour can become problematical at any temperature when mixed with air and the vapour content in air lies between approx. 1.9% and 8.6% for Butane (100%) or 2.4% and 9.6% for Propane (100%)... these are the combustion limit range values... all other mixes of these 2 gasses remain with these levels.
Self ignition temperature, in air, is approx 900deg F (482deg C).
When filling a tank via a Ronson type valve the liquid flowing into the tank displaces a small amount of vapour which actually flows out of the valve.
When the level of liquid in the tank reaches the bottom of the valve it spurts out of the valve, indicating that the tank is full.
In a correctly manufactured tank the valve is recessed into the tank body such that the bottom of the valve is at between 2/3rds and 3/4 of the tank capacity... thus ensuring there is sufficient vapour space above the liquid.
It is a very clever device really, albeit quite delicate and easily damaged with rough use.
I am not aware of any manufactured small gas tanks fitted with a gauge glass... the ones shown in Rhavranes video clip are the first I have ever seen but I am not sure if they are a standard manufactured item... they look more like custom built units to me, but I could be wrong.
I hope this answers your questions.
Stay safe.
Best regards.
Sandy.
