Method and apparatus for emptying vessels

Claim 1

A gas supply apparatus comprising first and second acetylene-delivering gas supply means for expanding acetylene gas and supplying same to an acetylene-gas consumer, each of said gas supply means including a respective group of tanks containing said gas under pressure, each group of tanks being provided with a respective withdrawal line, each of said withdrawal lines being provided in succession with a cut-off valve, a switch-over valve and an automatic pressure controller before said lines join to feed said consumer, a respective connecting duct communicating with each line between the cut-off valve and switch-over valve thereof and opening into the other of said lines between the switch-over valve and the pressure controller thereof, each of said ducts being provided with a respective switch-over valve, and control means including said controllers for initially drawing gas from said first gas supply means and upon partial emptying of said first gas supply means continuing to withdraw gas therefrom and to feed said consumer therewith in a preference stream, and for mixing said preference stream with gas drawn from said second gas supply means with progressive increase in the rate of flow of gas from said second gas supply means upon decrease in the rate of flow from said first gas supply means, the gas from said second gas supply means forming a complementary gas stream, said control means responding to comparison of the pressures of said preference and complementary streams with first and second set point values, each first set point value corresponding to a higher pressure level than the respective second set point value, the pressure controller of the line through which the preference stream is drawn having a horizontal or increasing characteristic curve while the pressure controller of the line through which said complementary stream is drawn having a horizontal or decreasing characteristic curve so that at a constant volumetric flow rate with a decreasing tank pressure, the pressure of the respective gas after expansion remains constant or increases over a broad pressure range for the preference stream and remains constant or decreases over a broad pressure range from the complementary stream.