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, that is the height of the accumulator ‘switch’. The on period at the base is small and high at the top and corresponds to low and high flows.

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).

In the picture on the left you will see the recorder drum has been removed and you see the integrator drum. At the rim of the drum there is a geared edge, which the ‘switch’ engages/ dis engages.

All this today would be done in a couple of lines of computer code, but do remember when these items where developed and I think you will agree extremely good design of the time and in fact systematically the same today, as the principle has not changed.