One of my projects for a gas supply company was the documentation of a computer controlled gas cylinder filling system, capable of filling multiple gases from the same set of manifolds, including mixtures.
Cylinders were brought to the manifolds on pallets, using forklift trucks, and flexible hoses were connected to each cylinder. The operator would then start a computer-controlled filling cycle, which involved venting and vacuuming the cylinders to remove unused gas, then filling them to the required pressure, taking into account the temperature rise during filling.
During the filling cycle, pumps would start and stop, valves would open and close, all under automatic control. The operator would not need to be concerned about what went on behind the scenes, unless something went wrong and an alarm was raised.
Documentation was required at both operator and system level. The operator needed instructions about how to perform the filling cycles and how to respond to alarms. The supervisors and maintenance staff needed more comprehensive documentation about the whole system, including the manual and automatic operation of pumps and valves.
In addition to gas cylinders, there was also a requirement for filling cylinders with liquefiable gases, for example carbon dioxide which exists in the liquid state under pressure at ambient temperature.
Mike Gascoigne, Write_on
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