In your picture is a Surge milking machine, those machines actully had a strap that went around the cow and under the handle of the machine this held the machine in the area of the cows udder so the teat cups ( the 4 shiny cans) could slid up on the cows teats, the teat cups had what was called an inflation inside the can. The inflation sealed both ends of the teat cup and the small line to the nipple on the teat cup got the pulsator vacuum, this pulsed on and off, when it pulsed on the vacuum would stretch the inflation out, then went the pulsator vented the vacuum out the inflation would squeeze the cows teat. So the pulsator would open the inflation then release it, stretch out, squeeze, stretch out, squeeze continually with constant vacuum at the end of the inflation through the claw which held the 4 teat cups sucking the milk the inflations squeezed into the milkers pail. This would actually simulate a calf sucking on the cows teats.
Surge, Universal, and Delaval had pulsators that worked on strictly vacuum, later they went to electrically controlled powered by vacuum.
A gas engine tractor could run one or two machines.
Most farms had an electric powered vacuum pump with vacuum lines run down the roll of stanchions in the barn.
When the power failed you would bring down a tractor and run a hose out to power the machines temporarily.