> now there's only one thing that can fail That's the sticking point. People tend not to think of mechanical systems as systems full of many components any one

> now there's only one thing that can fail That's the sticking point. People tend not to think of mechanical systems as systems full of many components any one of which can fail, but they are. In the case of the gas nozzle, you have the orifice for the airflow which can get blocked, you have the diaphragm which can break, you have the connection to the lever which can sever, you have the lever itself which can bind. Critically if it does fail, it fails catastrophically - gas spills everywhere. On the other hand consider a system employing a capacitive level sensor. When the sensor comes into contact with fluid, the dialectric constant changes and thus the voltage drop across the sensor increases to the point the valve will close itself. If anything goes wrong, say you lose power or a wire breaks or someone physically rips the nozzle off, the voltage still decreases below the cutoff threshold so the valve still closes - it fails safe. People like mechanical systems because they are easy to visualize, but that's not the same as being simple or safe. At the same time, most of our experience with electronics is with low cost consumer electronics where the price of failure is low and there is strong financial incentive to use cheap components with short life expectancies in configurations that aren't fail-safe, so we tend to associate electronics with being unreliable. But on a fundamental level, the force stopping two gears from passing through each other is exactly the same as the one producing a current when you apply a voltage to a piece of copper.