The April 16th article http://cryonews.blogspot.com/2009/04/cryogenic-liquid-cylinder-operation_16.html discussed why it is necessary to have a gas use coil that pulls liquid from the bottom of a 4L DOT Cryogenic Liquid Cylinder and vaporize it for gas use supply.And- It was noted that a pressure building system is needed to help maintain pressure within a specified operating range. So, how does the pressure building system work?
Liquid cylinders equipped with gas use coils also have another set of coils brazed to the inside skin of the outer jacket. Just like the gas use coils- the pressure building coils pull liquid from the bottom of the liquid cylinder and vaporize it. Vaporization happens by exposing the liquid to temperatures above its boiling point.
Unlike the Gas Use system, the Pressure Building system returns vaporized gas back to the head space of the liquid cylinders. Crowding gas molecules into this head space raises the pressure of the liquid cylinder. The pressure building regulator controls the flow of liquid into the coils and stops the flow of gas back into the head space.
It is important to note, though, that this does not stop pressure from building. Once pressure is raised on a liquid cylinder and warmer air is introduced into the top of it normal evaporation of liquid nitrogen, argon or oxygen will increase. Be sure that the valves feeding pressure building regulators are closed if the vessel is not going to be used over night or over a several day period. Venting of pressure and release of hotter air can also help minimize product lost due to normal evaporation.
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