18 votes
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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 ...
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13 votes
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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 ...
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  • 331
10 votes

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 ...
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  • 22.6k
10 votes

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 ...
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  • 341
7 votes

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 ...
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6 votes

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 ...
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6 votes
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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 ...
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  • 6,113
5 votes

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 ...
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  • 6,719
5 votes

Is it safe to use a 125PSI rated auxiliary air tank with a 150PSI air compressor?

Don't do it!! Just buy a pressure regulator to put between the two tanks that will decrease the pressure to below 125. You can get these for \$17 at home depot (https://www.homedepot.com/p/Husky-1-4-...
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  • 2,511
4 votes
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Turning an engine over with engine compression

In theory, it should perform as you say. This is how prop starting an aircraft engine works. An internal combustion engine, unlike your bike pump, is designed for high speed, high power, and high ...
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  • 7,444
4 votes
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How do you actually control the cooling level of AC?

The temperature of evaporated refrigerant gas is constant as a property of refrigerant material. And usually it is considerably below the thermostat setting in the controlled space. The design of the ...
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  • 20.9k
4 votes

Why are train brakes so complicated?

With an "spring apply / air release" system the spring pressure may not be enough to apply adequate braking force. Using compressed air to apply the brake allows much higher braking forces. ...
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  • 7,519
3 votes
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volume comparison of compressed air and gas duster

According to to the SDS found here the product contains tetrafluoroethane as an ingredient. I looked around and found other similar products with the same ingredient. For sake of simplicity lets say ...
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  • 593
3 votes
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Tubing for explosive gas or hydrogen transfer

I would say that it is true and for that case there will be many relevant codes / regulations that need to be respected. Make sure you read them all before designing / altering the system.
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3 votes
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Can Compressed air be used as a thrust component in a spacecraft to propel the craft through space or to orient the craft?

In the case of aircraft carriers the compressed air is generally a working fluid for a mechanical catapult rather than providing direct thrust like a rocket (steam is also used for the same job on ...
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3 votes
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Basic difference between "compress" and "pressurise"

As your question implies 'pressurise' can apply to increasing the pressure of any fluid whereas 'compression' indicates a change in volume. To illustrate; a typical industrial gas cylinder will be ...
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3 votes
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Are there any precedent designs for a mechanically-delayed pressure release valve?

There are three possibilities here that come up offhand, between my own mind and ratchet freak's comment: The choke that ratchet freak mentioned -- this is the simplest approach if you are OK with a ...
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3 votes
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How to design a hemispheric flexible pressure vessel?

This is fully doable. This is the in the higher range as bicycle tires (although with the outer tire as well and not the inner tube alone). Alright, here goes: What equations do I need to ...
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3 votes

Tankless air compressor for electronics desoldering station

For 1. and 2., you can solve the problem by having an adjustable valve from the output line to free air. This way you let some of the compressors output flow escape, leaving enough of flow and ...
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  • 1,835
3 votes

What is the best method to generate heat from a compressed air canister?

One possibility would be to use the air to drive a turbine (probably a radial turbine as they are used in turbochargers). The turbine could be connected to a generator and the generator to a resistor. ...
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  • 1,202
3 votes

Compressing gas with liquid

Yes indeed, air can be compressed by pressurized liquids directly as you suggest. However, there are problems that accompany this sort of scheme. First, if the gas is significantly soluble in the ...
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3 votes

Regarding design of a compressed air delivery system based on a screw air compressor

That is on the high pressure end of normal pneumatic conveying blowers, but they are out there. See the notice at the bottom of the attached chart. http://www.hsiblowers.com/products/high-speed-turbo-...
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  • 3,381
3 votes

Why do high pressure multistage air compressor have different piston diameter sizes?

There is a simple reason and a useful added benefit. As you compress air of a fixed mass it occupies less volume. If you give it more space again, it will immediatly decompress and the multiple ...
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3 votes
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Slow Driving an Air Compressor

Google dugout aeration windmill system. There are various makers. Here's one: https://koenderswatersolutions.ca/ The compressor on them does one cycle per revolution of the windmill. While not as ...
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3 votes

Is using your mouth and lungs to blow away dust inside your computer somehow bad for the computer?

Another option would be to use a vacuum cleaner, that way any dirt is not pushed inside the computer but its pulled outside.
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3 votes

Why are train brakes so complicated?

Because the system has worked for a long time and railroads don't want to spend money on improving a technology is time tested. Most railroads run locomotives that is over 25-50 years old. (Most north ...
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  • 31
2 votes

Is compressed air energy storage economically viable in the home?

The existing answers do a pretty good job of explaining the sizing and the economics, but surprisingly for an engineering site, skip over the equipment. And that's where this becomes totally ...
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2 votes

Is compressed air energy storage economically viable in the home?

I'm going to do some naïve math. So while charging your setup at night, you take in $x$ kilowatt-hours per hour. Multiply this by 7 hours, and you've taken in $7x$ kilowatt-hours. At a cost of $\frac{...
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  • 2,485
2 votes

Pneumatic Actuators - System Reversibility. Is it possible to use an actuator to store energy?

A,B,C, and D are normally closed solenoid valves. The valves with the arrows above them are pneumatic check valves, such as reed valves, with the arrow indicating flow direction. So basically, ...
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  • 3,525
2 votes

Can Compressed air be used as a thrust component in a spacecraft to propel the craft through space or to orient the craft?

The SAFER, used by NASA for EVAs ("Space Walks"), uses compressed nitrogen for thrust. Air is mostly nitrogen, and the properties are fairly similar. So, essentially it not only could be done, but ...
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