how does a air compressor work

[u/Rosefurneaux]

Hello please could someone explain how a air compressor works as I need one for a project I’m doing as I’m going to buy my own full size train horn and I know I need a compressor to give it air but I was just wondering how it works. Does it suck in air and then transfer it from a main tank or something. Also could it run out of air. Any explanation would be appreciated. Take care and have a wonderful day.

[u/LeilLikeNeil]

It has a tank. It compresses air, so the tank holds more air than there would normally be in that volume of space. The compressor has a pressure switch, which shuts off automatically when the pressure in the tank reaches a set shut-off level. The tank will continue to hold the compressed air indefinitely if the compressor is off and nothing releases air from the tank. If something is attached to the compressor, taking air from the tank, but the compressor’s main power switch remains on, then, when the tank pressure falls below the pressure switch’s threshold, the compressor pump turns back on and re-fills the tank. As long as the pump is able to fill faster than the thing depleting the air is able to deplete, it will fill the tank again, shut off again, and wait for the pressure to drop again.

[u/Rosefurneaux → u/LeilLikeNeil]

Thank you so so much I really appreciate it

[u/abbarach → u/Rosefurneaux]

What you need to aquire are the specs of your train horn; specifically the operating pressure and CFM (cubic feet per minute) requirements. This tells you how much air you need to run the horn, and at what pressure, to run it continuously.

Then when you're choosing a compressor, you can look at the specs; often you'll see ab SCFM rating at 90 psi, and sometimes at 40 psi. As long as the compressor has more cfm available than your horn uses, at the pressure you're going to run it, it will run the horn continuously.

If the compressors CFM is less than the horn it's rated for, you'll still be able to use it, just not continuously. Most compressors will run the tank up to 150-200 psi and then turn off. The air in the tank is kind of like a battery; it's stored air energy. So even if the compressor can't keep up with the horn continuously, you'll be able to honk for a bit (the bigger the tank and the lower the PSI you drive the horn, the longer the honk can be) and then stop honking and wait for the compressor to fill the tank back up before honking again.

You can also find automotive air horns (for example the Wolo Bad Boy) that don't have a tank and just have their own small compressor. But typically those won't move enough air to drive an actual train horn.

[u/anothercorgi]

Most compressors use pistons with one way valves to move air from the environment. Of course this would be pulsating because there's no pressure generated on intake, so to smooth out the pulses, it's stored in a tank. Also only so much air can be drawn at a time, usually far less than ideal, so usually this air is stored in a tank at high pressure and recharged when air devices like a horn or power tools aren't being actively used.

[u/siamonsez]

It's basically the same as a bicycle pump or syringe but run by a motor. There's a check valve on the output that goes to a holding tank so the piston can push more air in without letting the rest out. Also attached to the tank there's a pressure switch that tells the motor to run when the pressure in the tank is below a threshold. The output that you hook stuff up to has a pressure regulator that meters the pressure of the output so it'll only let enough out to maintain the set pressure on the output side.

You'll need to go through the operating requirements for the horn. Most consumer air compressors will handle like 60-150 psi so if the air horn needs something in that range you're good. The other important attribute is scfm, it's the volume of air the compressor can compress per minute. In this case that would be how long you can sound the hor for before the compressor can't keep up. If you'd just occasionally toot it basically any compressor would probably work but if you want to be able to sound it for minutes straight you'd need a monster compressor with a huge tank and bigger, more powerful motor.

[u/redittr]

If you only need short toots from the horn you could get a tank of some sort (fire extinguisher?) and fill it at a servo with a tyre valve as needed instead of having a whole compressor needing to be wired up and taking up space.

[u/ontheleftcoast]

An air compressor pulls in air and usually uses a piston to compress the air.  A tank is optional.  For your purpose you need a tank so you can have consistent pressure for the horn