# Tag Info

Accepted

### Why was Freon used in spray cans before it was declared a threat to ozone?

Spray cans work by containing a propellant which has a boiling point a small amount below room temperature. When the can is sealed the liquid and vapour reach equilibrium at a relatively modest ...
• 15k
Accepted

### Why does public transport uses compressed air to open doors instead of electromotors?

Do you mean, for example, a bus entry door? It may be as simple as the "service factor" for motors ("electromagnetic devices") as compared to pneumatics. Inexpensive motors with sintered bronze ...
• 331

### Why are train brakes so complicated?

This answer addresses the following sentence: So I'd expect to see the brakes applied by a spring that is capable of stopping the wheels of a fully loaded car, and a single-acting cylinder that works ...
• 22.6k

### Why are train brakes so complicated?

You need to consider what happens if a hose bursts, and your spring-applied brake locks the wheels on one or more cars - how do you get that train back to the depot? There could be a manual brake ...
• 341

### Why does public transport uses compressed air to open doors instead of electromotors?

They are smoother and if something gets caught in between them then the maximum force it can exert is capped depending on the pressure and the piston area. This means that a trapped limb is less ...
• 5,621

### Turning an engine over with engine compression

There is another reason for this in multi-cylinder engines. While one cylinder is compressing the air, another is decompressing it. The net result is that the torque as a function of position gets ...
• 11.2k
Accepted

### Why air compressing mechanism "Trompe" is not popular in usage?

Simply because it's so wasteful regarding energy. If you employ the flow and height difference of water for a hydroelectric generator to power a standard compressor (be it piston, centrifugal, or just ...
• 6,113

### Is compressed air energy storage economically viable in the home?

It isn't completely infeasible. Just to get a ROM (rough order of magnitude), let's assume that a typical household that isn't using electricity for heating uses about 1 kW on average, and that you'd ...
• 6,719

• 2,485