My Quiet Compressor Search

[TravisR100]

I had posted in another thread asking for advice on compressors. That thread is here:
Phase Converter Sizing & Compressor

I finally made a decision and wanted to pass along my findings. At this point I feel like I know more about compressors than I ever wanted to know. My requirement was to find a compressor that would supply my Haas Super Mini Mill 2 as well as a small blasting cabinet. I had a 5 HP 80 gallon unit that worked but it was old and ridiculously loud. It was a splash lubricated, not oilless.

For the Haas I need 4 CFM for the spindle plus another 6 CFM for the blow off. The 4 CFM needs to be constant and the additional 6 would obviously be intermittent. I do very little work with the blasting cabinet and would never be using it at the same time as the Haas. For that I need about 16 CFM but it would be about 80/20 duty even in use. All of these requirements are at 100 PSI.

My other main (probably biggest) concern is noise. I'm in a home shop so this compressor will be running in the garage and will be used a lot at night. I needed something that wouldn't annoy the neighbors.

Everyone immediately suggested the rotary screw compressors for the noise. I understand them to be very quiet. One of the problems with them is obviously the cost. They seem to start at about $3500 and go up with the Chicago Pneumatic brand being the least expensive I found. Once I started talking to screw compressor manufacturers the other problem they made me aware of is the need to run them for extended periods. Apparently if you don't run them long enough to heat up and stay hot there can be a problem with water getting into the oil. Most of the manufactuers I talked to said they really like to run 8 hours a day and run constantly. Since most of what I'm doing is hobby work it will be a few hours a night here and there. I was also told (by the people that sell piston compressors) that they require more maintenance.

So, back to searching. I found a couple of manufacturers that make a piston compressor in a prefab sound enclosure. Quincy is one of them. Here's a link to theirs:
http://www.quincycompressor.com/xtreme.html
Champion is another:
http://www.championpneumatic.com/Cha...id=10840&n=490

This looked pretty slick. But back to that cost factor again. They quoted me $3600 for the single phase, 5hp, 80 gallon model (and a 3 to 4 week lead time). That put me right back in low end screw territory price wise. So the search and research continued. I talked to Ingersoll Rand, Quincy, Champion, Atlas Copco, Shulz, and a few others I don't recall at the moment.

In my research one of the most suggested methods for quieting a piston compressor is to use a slower (1750 RPM) motor as opposed to a faster (3450 RPM) motor. Every major manufacturer I found that makes a 5 HP 80 gallon unit uses the 3450 RPM motor. Not until you get into the 7.5 or 10 HP units do they use the slower motors. I also found that with the faster motors they generally use a smaller displacement compressor pump. So they're running the smaller compressor faster to get the air and end up with more noise. I guess this keeps the cost down. Others have suggested simply replacing the motor but it seems senseless to buy a brand new compressor and have to change the motor. In addition some of the compressors must run at a minimum rpm to ensure adequate lubrication.

Another suggestion was to use one of the aftermarket filter/silencer units. I was told that it makes a difference. Once I read this my first though was to just put one on my existing compressor. My existing compressor however had a rectangular intake port and so I couldn't use one of these. More on the filter/silencer in a moment.

One other tip I found is to get a cast iron compressor as opposed to aluminum. I've read this makes a difference in the noise. I have no idea if it's true.

I had the guy at Shulz telling me they could custom build one with the slower motor and he assured me that it would be very quiet. He couldn't however define "very quiet" in dB. I asked if they could run one and use a dB meter on it and he said they didn't have one but if I mailed him one he'd check it and mail it back to me. So, I was worried about paying for something, having it shipped, getting it hooked up, and finding out it was just as loud as the compressor I just got rid of because of the noise.

On a whim I found a local compressor company through a Google search. I'm in Houston. When I talked to the guy on the phone he actually sounded pretty knowledgable and told me most of the same information I'd found doing research on the Internet. He said they had a compressor that they sold which they had put together based on their specs. It was a 5 HP 80 gallon unit with a two stage cast iron compressor and a Leeson (sp?) motor that ran at 1750 rpm which spun the compressor at about 700 rpm. Best of all I could drive over and go listen to it myself. And I did.

They gladly grabbbed their forklift and put one over in the maintenance area of their warehouse and hooked it up for me and ran it. I have to say, I was pretty surprised at how quiet it was compared to the compressor I got rid of. I'd say it ran at what subjectively sounded like half the volume. It seems that the main noise from these piston compressors comes from two sources. The motor/pulley and the intake port on the head. It had a filter on it. I asked him about the silencer/filter units and how much difference it might make. He pulled a couple of different models and screwed them on. The first one made pretty much no difference. The second one however made a big difference. I'd say it quieted down the intake noise by 20% to 30%. With the silencer on we could easily stand next to the compressor and have a conversation without raising our voices. Granted, this was in a warehouse well away from any walls. I have to imagine that when I get it powered up in my garage that it will be louder because of the enclosed space. Once I get it wired up I'll post back here.

Sorry for the lenghty post. To me it's always refreshing to find a local company with people who know what they're talking about and where I can put my hand on the product I'm buying. Hopefully this will help out others in their search.

[HelicopterJohn]

Here is a picture of a muffler that the guy on frets.com put on his compressor.

I don't know if if worked but the concept looked interesting. Just a length of rubber hose that helps deaden the sound.

John

[TravisR100]

As a matter of fact that guy at the local dealer where I bought the compressor today said that a length of PVC with angles or bends or hose attached to the intake would help silence it as well. He cautioned however against it because of the loss of flow that might occur. But it makes sense.

[rawen2]

Nobody gave an opinion on the other thread so I'll ask again here.
Anyone use a rotary vane compressor? They're supposed to be pretty quiet, and have a long life.
And Travis, how much were they asking for the piston compressor that you went to listen to?
Thanks,
Ralph

[TravisR100]

I looked into the hydrovane compressors. What I found was that there was really only one company that made them. Compair maybe? The others were rebadged. I also had no luck finding one small enough. They were all much larger units. Your mileage and research may vary. There was a guy here in houston that had one listed on eBay. I talked with him. He actually has about 8 of them. The probem for me was that they were all 480 volts. He seemed to think they were new-old stock as neither he or I could verify the model number anywhere. The voltage however made it a non-starter for me. I don't know if the suffer from the same alleged water in the oil problem that the screw compressors do. The biggest factor for me was ease of service and maintenance. I just finally decided the piston would also be the easiest to maintain.

I paid $1695. I didn't think it was a steal nor did I think it was over priced. It seemed like a fair deal based on prices for other units I looked at. I ended up adding on a coalescing filter and an auto tank drain. They threw in the silencer he tested it out with that seemed to work so well.

[Delw]

A friend at another shop has an older screw model, they are really quiet but very expensive. his is like a 20hp I believe he said it was around 15k new in early 2000 when he bought it.
he says its very fast and it doesnt produce as much water as the piston ones do. he has a seperate storage tank hooked up to it, its gotta be 200 gals.

when we bought our 15hp one we were looking at a screw one as well, but they were out of my price range at that time.
local compressor shops are always the best if you want quality,you will pay a tad more but if theres a problem they are a phone call away.
I bought mine back in late 90's and the company still calls me once a year to make sure I change the oil and maintence stuff. which is cool


Delw

[TOTALLYRC]

Good information guys.

Any info, price, or pics on the intake silencer?

I have an old 5hp cast iron compressor that has a lot of intake noise. I have it is in a separate section of the shop but you can still hear it and anything I can do to keep the neighbors and ears happy is worth investigating.

[Delw]

I ran a shop in our garage when I first started. a buddy of mine told me to put egg crates on the walls, I laughed one day I did it WOW worked good for the outside and alot in the inside as well.
dont forget the ceiling, just staple them around the lights

these are the eggcrates you get at restruants and the ones we machines shops use for small parts

[TravisR100]

The silencers seem to run about $15 to $40. Here's a link to them on Grainger's site:
http://www.grainger.com/Grainger/wwg...lencers%2C

[TravisR100]

Obviously I have no affiliation with the company I bought the compressor from, however if anyone's interested it's Quality Electric in Houston. Seems like compressors is all they do. Apparently in business since 1959. And I'd believe it after seeing their facility. It looks like they've been collecting compressors and compressor parts for that long. Their number is 713-225-6531. The guy I talked to that knew his stuff was Charles Jr.

[DareBee]

Make a quick and dirty plywood box around the compressor and line it with "egg-crate" foam.
The foam is cheap and really works.
You may not even know you have a compressor after doing that.

[Delw]

that works but make sure you add a fan in and exhuast out.