Today it seems that we have become accustomed to tasks that formerly were the responsibility of the driver to be delegated to the technology. The headlights on our car turn on automatically when you enter a tunnel or it gets dark, the wipers are activated when they begin to fall a few drops, and even increasingly, cars are equipped with systems that prevent us to get out of our lane if we release the steering wheel. But at the dawn of the automotive industry, the situation was very different. Can you imagine having to manually move the wipers or push fluid to clean the moon of your car by squeezing a bulb with your hand? Back in the sixties Volkswagen would find a solution even smarter, to take advantage of the air pressure of the spare wheel to pump the windshield washer fluid.
This idea that advocated for the simplicity and intelligence, intended to dispense with an electric compressor that bombease the fluid up to the windshield.
Until then, the Volkswagen Beetle had used the solution of a diaphragm driving manually the liquid from one tank to our windshield. It was at the beginning of the sixties when, trying to find a solution that is more comfortable, Volkswagen opted to take advantage of the air pressure of the spare wheel to avoid the technical complexity of an electrical air compressor.
But what happened if the driver of a Beetle with this wiper system suffered a puncture?
The spare wheel should get a inflated above the recommended pressure by the manufacturer to ensure that the wheel out-functional in case of a puncture.
The system, complex as it may seem, was even more straightforward than the mechanism of a jug. The tire valve was connected directly to the water tank and windshield washer fluid, to pressurize the vessel at the time of opening the valve that allows you to pump the fluid up to the windshield (see image of the manual of the Beetle shared by a user in this thread from reddit).
The valve responsible for pumping the fluid up to the windshield also had to cut off the flow of fluid at the time at which the pressure of the spare wheel falls below what is advisable by the manufacturer, for below 28 psi. To avoid problems in case of a puncture, the spare wheel of these Beetle should be inflated above the recommended pressure for your use, between 42 psi and 56 psi. In any case, it seems that in some markets commercialized versions of the Beetle without this valve, which could generate situations a bit awkward, like djing and having a spare wheel without a pressure sufficient to roll.