gallon

To get from flow to gallons you have to integrate flow with respect to time.

For a given period, you can measure the flow and accumulate this. Notice the picture, the drum is rotated at a given speed (time interval) and there is a step on the drum. This turns the integrator on and off, dependent on the amplitude of the flow.

This mechanical switch, then engages dis-engages the accumulator, which makes up the gallon meter. The position of the roller switch is proportional to flow (differential pressure).

Notice the cog to the barrel gear. Hence, dependent on the amplitude of the flow, determines how long the accumulator is on and off in a given period of time. This is a mechanical integrator, it measures the area underneath the flow plot, to give volumetric measurement. What could be simpler. Today this process would be done in a computer, but using the same approach!

Here we have the hole meter. To the right is the recorder, top the clock and to right the integrator and below the accumulator (gallons meter).

In hindsight it sounds a straight forward system, and that's because we have applied a systematic approach to its design. Its counterpart is now in the realms of sensor, interface and computer, but the basic system is still the same.