Tip: Reducing compressor noise.

My 3.5 hp oiled compressor is noisy when running to the point where a conversation cannot be held while it is running. So this weekend, I built a compressor box which I thought might be of some interest to others.



The box is made of 18mm MDF, and measures 1.2 x 0.8 x 0.6m. It is bottomless to fit over the compressor, and the double thickness lid is removable.



The air feed is taken out through the side (front?) wall into a water condenser and teed to a quick connect for painting. From there it goes through an oiler to two regulated quick connects - one set to ~80 psi for drilling, and the other set to ~30 psi for rivetting.



With the lid removed, you can see the compressor inside the box. The box has a single thickness wall, with an "E" shaped baffle at each end to allow air to flow through the box without letting too much sound out. The inside of the box is lined with rubber carpet underlay, and a power strip is mounted inside the box to deliver power to the compressor and a 12v power supply for the extractor fan on the outlet side.



With the lid propped up, you can see the double thickness lid, which fits very snugly inside the top - a quality fit is essential here to keep the noise inside the box.



The aluminum vent covers the baffle inlet, which is routed upwards through a series of MDF baffles to enter the box via a 120mm hole on the inside. The other end is identical but has an 80 cfm fan to assist in the movement of air through the box. You can also see that the compressor and the box are sitting on double thickness of underlay, which is used to prevent compressor vibration being transmitted via the concrete floor to the box.

Well, I was surprised just well it worked. When the compressor is running, it is now only slightly louder than a chest freezer. Noise levels are vastly improved over the compressor alone.

How am I going to improve it? My next job is to put an access hole in the front so that I can easily check the oil level and drain the tank regularly - "out of sight, out of mind" is definitely a bad idea in this instance. I will also connect a temperature probe inside the box to a display readout outside and use it to trigger the extractor fan when the temperature gets too high. Only then I will be happy that I am not going to destroy my compressor through overheating. I am also going to make the lid pull double duty for tool storage by fitting a piece of foam to the top and cutting out holes for airtools, bucking bars etc.

This mod has made my workshop a much more pleasant place to be.

Chris,

Great job on the compressor silencer box! My compressor is a Sears oil-less variety and you can't scream loud enough for a conversation while it is running. I am about to start riveting again and dreaded the noise, so the timing of your thread is perfect. I am off to Home Depot for some material. Thanks for the inspiration!

Jim

Heat may be a factor, the compressor gets pretty hot with alot of use. May need to add a fan and some vents.

I built something similar (although not quite as nice). It was ventilated but it did burn up two compressors. I would use caution.

Gotta agree with the advice about heat-------I would look at ducting the outflow side of the units cooling fan out to the exterior of the shop, and provide adequate inflow air for make up.

Also, the pressure regulators ganged together, ????? If you have trouble keeping the low side accurate, try splitting the feed with a "T" so each one sees tank pressure.

The drain can be run outside of the box, valve where it can be easily reached. Right now it looks like you might need an extra elbow in your arm to reach the drain.

Otherwise great job. I really like the idea of storing the tools on the lid in designated cutouts.

Kinda off topic as usual, but someone told me about a guy who uses windmills to pump air into storage tanks (a bunch of em), and he uses this as an air and multiple alternative energy source (pneumatic electric generation). I'll bet that's a quiet air source, if you don't mind air tanks everywhere. The compressor noise has driven me to as many electric tools as possible. I keep looking for an electric rivet gun. Any ideas?

aerhed said:

The compressor noise has driven me to as many electric tools as possible. I keep looking for an electric rivet gun. Any ideas?

Click to expand...

UHMmmm change your screen name???

To what?

"UHMmmm change your screen name???"
To what? Maybe "Pompous airplane expert"?

Missed my humor a bit. Note the

"Aerhed" sounds like air head.

And you dont like air compressor.........

As usual, just livin up to my name. You okay?

aerhed said:

As usual, just livin up to my name. You okay?

Click to expand...

Just fine.

Mike S said:

Gotta agree with the advice about heat-------I would look at ducting the outflow side of the units cooling fan out to the exterior of the shop, and provide adequate inflow air for make up.

Also, the pressure regulators ganged together, ????? If you have trouble keeping the low side accurate, try splitting the feed with a "T" so each one sees tank pressure.

The drain can be run outside of the box, valve where it can be easily reached. Right now it looks like you might need an extra elbow in your arm to reach the drain.

Otherwise great job. I really like the idea of storing the tools on the lid in designated cutouts.

Click to expand...

Those are great ideas, Mike. A tee junction to each of the oiled regulators makes a lot more sense (doh!!), as does running the drain to the outside.

I am keeping a VERY close eye on temperature and airflow, and will let everyone know of any mods I may need to make to address heat build up.

Thanks for the feedback everyone - this is a great forum and resource.

JAT said:

Chris,

Great job on the compressor silencer box! My compressor is a Sears oil-less variety and you can't scream loud enough for a conversation while it is running. I am about to start riveting again and dreaded the noise, so the timing of your thread is perfect. I am off to Home Depot for some material. Thanks for the inspiration!

Jim

Click to expand...

Thanks Jim. I'm not sure what it is about compressor noise, but for some reason it is much more wearying and oppressive than drill or rivet gun noise. If you are interested, I will take a photo tonight of the inside of the baffle... Also check out Mike's comments about not ganging the two tool regulators in serial. Parallel makes a lot more sense.

Another idea

I put mine in my basement years ago when the boys were still at home. Draws in CLEAN cool air year-around, and you can barely hear it run from my attached garage. Just drilled a hole thru the wall into the garage. Did the same with the power. Have a HD switch in the garage to turn it on and off. Works great.

John Bender

170 driver said:

Heat may be a factor, the compressor gets pretty hot with alot of use. May need to add a fan and some vents.

Click to expand...

Yup, that is a very real concern. There is already one fan and baffled inlet/outlet vents, and I will be keeping a VERY close eye on temperatures.

A lot of thought went into the positioning of the internal inlet vent so as to put cool air in the best place for the compressor fan to put it over the vanes, and the positioning of the extractor fan to pull heated air away. I fully anticipate having to add another fan on the intake side to assist in the airflow, and will be setting thermometer alarm alerts on 20 degrees over ambient.

If the compressor is running continuously (such as using my HVLP gun or die grinder which just seems to dump a LOT of air) I can always just take the lid off for those jobs.

The big danger as I see it is complacency and "out of sight, out of mind" will quickly lead to a burnt out compressor.

Nice work

Nice work!

1. You need periodic access to check the oil, and visually inspect the compressor. Check, covered.
2. What will happen with an air leak in the shop, and continous operation?
- can you remove enough heat? How hot is your compressor running?
3. You need periodic access to drain the water off the tank. Check, covered
4. Indirect air paths are quieter than direct, nice job, check.
5. Isolating the enclosure from the surrounding structure can make a big noise reduction. Check.
----------------------------

I built a standalone structure, 2x4 skinned with 3/8" plywood and insulated and vaporbarriered (to retain the insulation). I perforated (1/2" holes)
I have a stand-up model on rubber pneumatic tires, and a rubber bumper under the skid leg opposite the tires. This provides isolation from the floor - I didn't have to isolate the structure. Sleeved hose from the compressor through the housing wall also helps to reduce noise.

I built it tall enough to put a standard bathrooom fan in over the compressor head, and duct it overboard into the garage. I haven't had any complaints about the waste heat in the garage yet.

For me, one side fits snugly, and is removable. I can roll out the compressor to use elsewhere if needed - haven't had to do that yet.

I have the compressor and the fan on a little controller, I've seen it done with timing relays (thanks Mike P.). I push the button (well, I have a kid for that) and the compressor charges up, the exhaust fan runs.
It's set up so the exhaust fan runs 10 minutes longer than the compressor, which is allowed to run for up to half an hour.
After that, the kids take turns pushing the start button
Worst case continuous run for me is the half hour, even if a line comes apart in the shop somewhere - hopefully avoiding the air-compressor-started fire scenario, and maybe the compressor-cooking-itself scenario too.

I mounted an indoor/outdoor thermometer on the outside of the housing, and put the sensor on the inside top, over the cylinder. It records current temperature and the max.

The only serious complaint is that the bathroom fan is too noisy, SWMBO says it needs to be quieter too, if she's going to paint in the garage while I'm working. I should have spent another $20 on a quieter model.

Here's my version of soundproofing my oiled compressor. It's lined with bed foam from Bed, Bath and Beeeeeyond.

http://www.smittysrv.com/more_stuff.asp?ID=7

Heat solution: what about a poor man's radiator?

chinch said:

Yup, that is a very real concern. There is already one fan and baffled inlet/outlet vents, and I will be keeping a VERY close eye on temperatures.

A lot of thought went into the positioning of the internal inlet vent so as to put cool air in the best place for the compressor fan to put it over the vanes, and the positioning of the extractor fan to pull heated air away. I fully anticipate having to add another fan on the intake side to assist in the airflow, and will be setting thermometer alarm alerts on 20 degrees over ambient.

If the compressor is running continuously (such as using my HVLP gun or die grinder which just seems to dump a LOT of air) I can always just take the lid off for those jobs.

The big danger as I see it is complacency and "out of sight, out of mind" will quickly lead to a burnt out compressor.

Click to expand...

Any chance you can employ a similar radiant cooling concept to what a lot of folks are doing in the planes with an ice chest and a 12V fan? If you used the baffle area and had a location for ice or cold water, you could cool the intake air. Am I crazy?

cattflight said:

Any chance you can employ a similar radiant cooling concept to what a lot of folks are doing in the planes with an ice chest and a 12V fan? If you used the baffle area and had a location for ice or cold water, you could cool the intake air. Am I crazy?

Click to expand...

Crazy or not, I'm not sure what is being referred to - can you point me in the direction of a picture or forum posting so I can better understand?

Couple of other things I didn't mention. One embarrassing moment was getting halfway through the build only to realise that a LOT of noise was coming from a loose plastic cover on the electric motor which was vibrating like crazy - a couple of shims fixed that - so if compressor noise is an issue for you, make sure you look at the obvious causes FIRST, before leaping all the way to an possibly over engineered solution...

The other thing was how brilliant the air fittings were to work with. These have changed a lot in ten years, and it was brilliantly simply just to push fit them all together. I don't know what they are called, but they were worth every penny!

("What's that dear? Every penny? It's just a saying - no, they weren't *that* expensive.... here, look how nicely they all line up, and it's going to make things SO much easier, and did I mention how nicely they all line up???")

One more thing to check.... wire gauge

Chris:

Check the wire gauge on the strip you are using to plug in the compressor. The wire gauge on the strip should (at least) as heavy as the compressor wiring.

Some of the less expensive strips use 18 gauge wire which may shorten the motor's life.

Good job. Anything you can do to make the building environment more acceptable will shorten the build time.

MrNomad said:

Chris:

Check the wire gauge on the strip you are using to plug in the compressor. The wire gauge on the strip should (at least) as heavy as the compressor wiring.

Some of the less expensive strips use 18 gauge wire which may shorten the motor's life.

Good job. Anything you can do to make the building environment more acceptable will shorten the build time.

Click to expand...

Thanks Barry, will definitely check that out. Could you please explain why a lighter gauge would have that effect?

For anyone who is interested, here is the inside of one of the baffles. These were constructed as two separate boxes (one for each end) around which the rest of the box was then built. I was initially concerned that without a top and a bottom, the box would have insufficient shear strength, but the 18mm MDF and the depth of the baffles boxes were more than sufficient to prevent twisting without any internal cross bracing needed.



Now back to rivetting practice....

Why heavier gauge wire is preferable....

Chris:

I am not an EE but can speak from practical experience and offer a layman's understanding. The issue deals with watts, amps & energy. A certain amount of energy is required to turn the compressor motor. If the thickness of the wire is too thin, the electrons cannot flow easily and result in heat. Voltage drops too so instead of sending 115v, you may deliver only 100v.

Think of a garden hose. If the diameter is too small, the volume of water delivered is constrained.

A million years ago, when I was a young man, I installed a pool in the backyard. #10 wire was called for given the distance between the house and the pool motor. I queried the electrician and asked how much extra $$ #8 wire (thicker) would be. The difference in $$ was miniscule, but he smiled and suggested the motor would prob last a long longer.

He was right. Whereas my neighbors changed motors frequently, mine lasted for more than 15 years.

Suffice to say, wire is cheap so better to be too thick than too thin. At the very least, make sure the extension is the same gauge as the wire to the compressor. Also make sure all connections are good and tight. Some of the strip internals are really poor and so are the strip switches & strip breakers.

Those are other ways to lose energy and decrease compressor life.

Glad to help.

Here's an update...

I've made a couple of modifications to my compressor box while I save up for my -8QB kit.

Firstly, I added a frame, handles and a first layer of closed cell foam to the lid in preparation for the tool cutouts. I've also routed the tank drain to the outside of the box.



The lid frame has a digital thermometer with the sensor mounted inside the lid directly above the compressor cylinder head.





The thermometer was very revealing as to what was going on inside the box. When the compressor starts up, the temperature increases slowly, at a rate of about one fifth of a degree every few seconds.

As soon as the compressor stops running, the compressor fan stops turning, air stops flowing across the vanes, and the rate of temperature increases dramatically to a full degree every second or so (all temps are in Celsius).

A short compressor run of about a minute caused an increase of about 20 degrees, which then took about 30 minutes to return to baseline.

Now I know why boxes like this can cook compressors. A quick check on the web determined that rubber, foam, and MDF will not combust until things get way above triple digits, so at least I have an idea where my safety limits are.

Time to get some air flowing - the small fan on the outlet side was doing very little.

Step 1. I cable tied four 120mm fans from the computer store together in a 2x2 matrix, and then cable tied the result directly to the compressor fan inlet. When the big fan stops turning, the little fans keep moving air across the cooling vans (sorry for the less than clear picture).



This made a big difference. Both the rate of temperature increase and the overall temperature rise were halved. Return to a baseline was also much quicker, but not so quick as to give me any comfort that long sustained running (e.g. HVLP, die grinder) would not create more heat than I could get rid of.

Step 2. Get more cold air into the box. I purchased a cheap $10 fan heater, removed the grill and all heating elements, and built a duct to direct air into the inlet side.



I mounted the fan vertically to minimise the footprint and the chance of workshop chaff falling into the fan inlets. The curved intake is intended to provide additional clearance between the fan and the inside of the inlet baffle.

I have yet to do a timed test to see how well this assists airflow, cooling and return to baseline, but a test run shows that the fan is certainly moving a lot of cold air into the box.



So here is the final configuration (with the lid open). More than likely, there will be some more tweaks down the line (cutoff valves upstream of the quick releases, reconfiguring the layout of the regulators, etc), but I am comfortable that short of actually putting a compressor inside a working chest freezer, I have taken strong, positive steps to addressing heat issues.

So, why the salmon pink colored closed cell foam? Why, it's a salute (cue Tim Allen *swish*) to Doug Reeves' scooter! *grin*

Closing the loop

Well, I finally got around to doing some measuring of what is going on inside the box - and no surprises. Moving air around is critical to keeping the temperature down - and therefore prolonging the life of the compressor.



Three separate runs across three consecutive nights in three different configurations - no fans running (cyan), all fans running (green), all fans less outlet fan (purple). When the tap is open and the compressor was running are shown as red and blue lines at the bottom of the chart.

The procedure was the same each night. From cold, open the tap, turn the compressor on, let the compressor free run for three minutes to get the oil moving, close the tap. At 10 minutes, open the tap for two minutes. Temperature measured inside the box immediately above the cylinder head every 30 seconds. I know this is not typical usage pattern, but I wanted to give the trends some time to establish.

Y axis is temperature in Centigrade (100°F = 37.7°C). X axis is elapsed time.

I could do more tests of other configurations to find out which fan is most effective, but this is just a compressor box, after all.

If you are thinking of doing something similar to what I have done (which has been very effective in making my workshop a quieter and more pleasant workspace), keeping air moving across the cylinder head AFTER the compressor has been running, and moving cold air into the box is absolutely essential to not cooking your compressor.

My last mod will be to put the fans on a thermostat so whenever the temperature inside the box gets above 20°C, on they come.

(...I really do need to get my kit ordered...sigh.)

Go forth young man!!

Chris:

Anyone who goes to that much trouble to insulate a compressor is likely to build one helluva great airplane.

You said: "(...I really do need to get my kit ordered...sigh.)"

I agree!

chinch said:

My last mod will be to put the fans on a thermostat so whenever the temperature inside the box gets above 20?C, on they come.

Click to expand...

Be careful when you do this, set the "on" temp well below the desired run temp, you do not want the cooling system to be playing "catch up"----get the cooling air moving before it is needed.

I started with a thermostat

But I took it out to simplify the system. I don't think it's necessary, except perhaps as HIHI temperature alarm, or to trip the air compressor off for Too Hot.

Now, if my compressor runs, the bathroom exhaust fan I put in the top rear runs. The exhaust fan also runs for 10 minutes longer than the compressor is allowed to.

My compressor runs for (max) half an hour, then times out and wants me to push a button to enable it to run again (if the pressure switch calls for it).

I found that if I was running the compressor, I was always running the exhaust fan shortly anyway (enclosed space heats up quick with not much air flow, I found).
----------------------------
Start button - compressor enabled for 30 min, exhaust fan runs
Stop button - compressor disabled (and stops if running). Exhaust fan starts timing down 10 minutes.
Stop button again - exhaust fan stops now (doesn't wait to time out)
-----------------------------

I wanted postive control of when the compressor can run, to avoid an air leak resulting in a fire, at least when I'm not around.

------------------------
I'm still trying to figure out how to adapt your tool holder idea - that is very appealing to me.

Why are there 3 regulators?

Why are there 3 regulators?

MrNomad said:

Chris:

Anyone who goes to that much trouble to insulate a compressor is likely to build one helluva great airplane.

You said: "(...I really do need to get my kit ordered...sigh.)"

I agree!

Click to expand...

I would almost say is likely never to finish an airplane

You must...

...be an engineer.

chinch said:

Well, I finally got around to doing some measuring of what is going on inside the box - and no surprises. Moving air around is critical to keeping the temperature down - and therefore prolonging the life of the compressor.

<snip>

Click to expand...

Ouch!

gimp2x said:

I would almost say is likely never to finish an airplane

Click to expand...

Mike, that has sharp edges, given my history!

Let's put it this way, if I ever finish an airplane, it will indeed be "helluva great". - Thanks, Barry! Helluva nice thing to say.

Hmmm...

mcencula said:

...be an engineer.

Click to expand...

Actually, I'm a systems designer and company founder. (TracPlus is my baby - www.tracplus.com)

Officially, I'm just trying to keep my idle hands doing something while I wait until I can afford my kit, and trying to get into the habit of doing something in the workshop each day. That's a bit hard in the winter when my infinitely better half has LOTS for me to do inside the house, which is nice and warm....

Unofficially, the combination of my OCD and desire for peer approval from this forum probably made such a graph inevitable

Because...

The Wizzard said:

Why are there 3 regulators?

Click to expand...

Thanks for asking!

One for unoiled air at painting pressure, another for oiled air at drill/die grinder pressure, and another for oiled air at rivet gun pressure.

The last two should be in parallel, not series (see earlier suggestions for improvement in this thread).

But that's a project for another time.

I applaud your effort, ingenuity, and what looks like great results.

chinch said:

Thanks for asking!

One for unoiled air at painting pressure, another for oiled air at drill/die grinder pressure, and another for oiled air at rivet gun pressure.

The last two should be in parallel, not series (see earlier suggestions for improvement in this thread).

But that's a project for another time.

Click to expand...

Wow
I have the same old (used) 5hp vertical De-Vilbiss that I bought for next to nothing. I rebuilt the compressor end 10 years ago. It leaks a little oil now.

What I did was mount the feet on some commercial grade Lord mounts.

It is also on a platform suspended from the 10 foot ceiling on a 2 foot x 2 foot platform that the lord mounts attach to.

It makes it quieter by the feet not touching the hard and resonant concrete floor.

I can tell that yours must be quieter, but you have invested alot of time in it.
Its fun getting ready to build, its even more fun building!

Best Wishes.