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What makes a quiet air compressor quiet?

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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.

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