I occasionally meet students who perform maintenance in less-developed countries. They often tell intriguing stories of resourceful local technicians who do not have some of the tools we take for granted. The stories always seem to include duct tape, baling wire, etc. It is fascinating to hear tales about how they get by with what they have.
One such story caught my attention because of its connection to physics: A student described a local technician who knew how much refrigerant he needed to weigh into a system, but did not have a proper scale. How could he accurately weigh in the charge?
The technician rigged a simple scale using a balance beam attached to a pivot point. A refrigerant cylinder hung from an attachment point at one end of the beam. On the other end, the technician attached a bucket and began filling it with water. Eventually, the bucket of water and the cylinder weighed the same and delicately balanced out.
Knowing the amount of volume a given weight of water occupies, the technician was able to calculate the water volume that would equal the weight of the refrigerant he needed to add to the system. Using a measuring cup, he carefully removed the volume of water equal to the required weight. Of course, the balance beam became unstable, and the refrigerant cylinder dropped down. At this point, he was ready to charge the system. As he gradually added refrigerant to the system, the cylinder rose back up and balanced with the bucket of water. He had weighed in the charge with some degree of accuracy based on a calculated volume of water weighing a given amount. All in a day's work when you do not have modern electronic gadgets.
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