CO2 – A Darker View

In this age of short product lifecycles and rapid obsolescence it is nice to see an example of longevity. We consider equipment or tools old when over ten years in service. How about a century?

A compressed gas cylinder with inspection dates spanning over a cetury — A compressed gas cylinder with inspection dates spanning over a century

Our CO₂ is delivered in standard industrial pressure cylinders. These steel cylinders hold 50lbs of liquid CO₂ at a pressure sufficient to keep it liquid at room temperature, about or about 800PSI.

These standard cylinders require inspection every five years, and the inspection date is stamped into the steel at the top of the cylinder in the format month-year with a two digit year. It has been this way for a long time, longer than I realized.

The usual drill… A problem that can be solved by a bit of circuitry. In this case the gals in the lab were having trouble controlling the mix of gas to their cultures. They needed to feed much less CO₂ to the mix, where the off-the-shelf flow gauges and needle valves became difficult to use much under one liter-per-minute.

Simple solution… Build a gas modulator, something that could turn on the gas some percent of the time, allowing easy control of small amounts of CO₂ to the mix. A timer and a gas solenoid… Easy.

There is nothing particularly interesting about the circuitry. A seven segment display, a few switches, and a power transistor to control an external solenoid. All very basic. It is the controller that is new, at least for me. An Arduino provides the programmable part of this project.

Tag: CO2

A Century in Service

A Gas Modulator