What makes a quiet air compressor quiet?

[Berni]

Yeah most things that insulate acoustic noise will also thermally insulate pretty well.

The motors are generally wound for maximum power with minimum material, rather than maximum efficiency so they produce a fair bit of heat. Then the compression of air is basically a heat pump too.

There are silent marine diesel generators that are put inside insulated boxes, those run coolant lines out of the box to dissipate the heat, but on a boat you got a convenient large volume of cool water right under you.

[unknownparticle]

Well of course the inlet and exhaust air ports would need some thought but I have used compressors that have manufacturer enclosures that work no problem, and have made enclosures for a couple of compressors myself, it's not that difficult.  Even with inlet and exhaust ports the reduction in noise is significant.  Here's a nice little unit I used for a while, for some idea.

[edpalmer42]

If you start with a noisy compressor, you have two options.

First, you use a good muffler on the intake to suppress the noise from the air movement and the valves.  That's a relatively easy DIY project and is appropriate for any size of compressor.

Second, you build an enclosure around the entire unit to suppress all noise sources.  As Kleinstein stated, the heat generated by the compressor has to be taken into account.  Usually, the result is a fan-forced enclosure where both inlet and outlet vents are in the form of a labyrinth that has foam-lined walls.  The entire interior of the main cavity is also foam-lined.  This technique becomes awkward with large compressors because you're building something the size of a garden shed!  I've never seen a project where the compressor was seperated from the tank and enclosed seperately.

The results of either option can be quite impressive.

But the intent of this thread was to explore how some compressors manage to be relatively quiet without requiring either of these extra steps.  We've seen examples of extremely quiet units, but it looks like they achieve low noise at the cost of low air volume.

I hoped that we'd hear from someone with better information on the design of these relatively quiet units, but that hasn't happened.  But the discussion has been very interesting and useful.

Ed

[Andrew LB]

Some of the newest air compressor designs no longer use pistons, but rather twin helical screws. The twin rotors don't touch each other but are of an interlocking shape so they fit perfectly and the air gets sucked in on one end and pushed towards the other end, compressing it in the process. It's a bit like a supercharger on a car, the big ones that bolt on top of the engine.

here is what the compressor looks like.


I'm not sure if this is what is being used in those "quiet" pancake compressors, but it's definitely the tech used in larger vertical compressors like the type i'm looking into buying to replace my Craftsman 26 gallon compressor. My Craftsman is about 93dba while running and these rotary compressors seem to be around 60-68dba which is a massive improvement.

[james_s]

That's a screw compressor, they've been around for close to 100 years, they're more expensive than reciprocating compressors though.

The quiet pancake compressors are modified reciprocating refrigeration hermetic compressors.

[BlackICE]

Also can look up scroll compressors they are also quieter.

[DarkMode]

To ask what makes an Air compressor Quiet, you are asking What makes a good Circuit board... the Answer is Complicated.

  However I do have a suggestion for you, which maybe NOT suitable for you.
12V Fridge compressors, aka - Single Spring Piston Pumps - You see these in Engels, EvaCool style units.

Food for thought.

[DarkMode]

A Diaphragm compressor might what you are looking for, moderate flow, moderate noise.

Screw type compressors aka Super-Charger styles could work and they are used in Commerical Units (at a cost), you still need to spin those at Engine speeds (2000 rpm onwards)
I only mention this because I seen a post where some listed these.

  There is no simple answer, just like Electronics 

[BlackICE]

A Diaphragm compressor might what you are looking for, moderate flow, moderate noise.

Screw type compressors aka Super-Charger styles could work and they are used in Commerical Units (at a cost), you still need to spin those at Engine speeds (2000 rpm onwards)
I only mention this because I seen a post where some listed these.

  There is no simple answer, just like Electronics 

I have a spare 2.3L screw supercharger from my car that I replaced with a 3L supercharger. I wouldn't think of using it for an air compressor because it would have to spin at least 5000 rpm to make pressure needing a lot of power. Also there is air leakage on the rotors, spin to slow and the leaks negate any pressure on the output. Besides it is designed to only put out about 1 to 2 bar of pressure.

[james_s]

I have a spare 2.3L screw supercharger from my car that I replaced with a 3L supercharger. I wouldn't think of using it for an air compressor because it would have to spin at least 5000 rpm to make pressure needing a lot of power. Also there is air leakage on the rotors, spin to slow and the leaks negate any pressure on the output. Besides it is designed to only put out about 1 to 2 bar of pressure.

Is it a screw type or a Roots blower? Either way they are not all alike, screw compressors intended for use in industrial air compressors are fairly common, they're specifically designed for higher pressure and lower volume than a similarly sized automotive supercharger. My friend's shop has two big screw compressors, I think they're 15 or 20 horsepower, very quiet relative to the 10 hp reciprocating compressor they used to have.

[BlackICE]

screw type.

[DarkMode]

Is only you could 3D print such items 
add some Electroplating
spin it up 

[BrokenYugo]

Practically speaking for small quiet shop type compressors, as far as I know you're pretty much looking for Jun Air (buy used) or belt drive. You can slow down the belt drive compressors to a point to quiet them further with a smaller motor pulley, but you need a minimum RPM for proper splash lubrication, and enough belt wrap on the motor pulley to actually transmit power, some stock ones I've seen are about as small as you can get already.

The automotive guys I know will typically put the main one in a closet, little enclosure outside the building (bad idea with close neighbors), shed, garage attic, basement, etc. Just separating yourself from the thing with a wall or two helps a lot, running an air line is pretty cheap.

[Old Printer]

I don’t know the technical reasons behind a “quiet” small compressor, but we use them at work for the air injection system on our lasers. For years we have used cheap pancake compressors made for nail guns, they make enough noise to wake the dead, but are cheap. Ours are inside the work space and create a level of noise that prohibits conversation when running. We recently bought one of the Mikita Quiet series units that are about three time what we paid for the HomeDepot basic Porter Cable ones. The difference in noise level is astounding, you can stand next to it in a small room and easily talk over it. Just amazingly quiet, like at first you wonder if it is working right until you see the gauges ramp up. I have studied air gun silencers/moderators a bit and suspect a similar approach is used for the compressors, plus the expected vibration dampeners etc..