Question About Air Compressors

Wrecked944 · 11-18-2004, 10:44 AM

Always the cheapskate DIY mad scientist, I started to ask myself why air compressors are so expensive. And the answers seeemed to be that a good air compressor needs to have a high psi rating and lots of air flow capacity. If I understand correctly, this means I should be able to run big power tools straight off the compressor even when the tank runs out of air. And it means the tank will, theoretically, fill quickly when emptied.

But I'm a pretty patient guy. And nobody is holding a clock over my head when I tinker with my car. So if the tank runts empty, then I really don't mind taking a break until it refills. So if I were to buy a cheap 1hp or 2hp compressor that were rated at, say, 125psi and then used it to fill a HUGE freaking air tank (maybe 15 to 20 gallons), then why should this not meet nearly all of my amateur wrenching needs?

Am I thinking too much here? Or is this a sensible idea?

turbo6bar · 11-18-2004, 10:57 AM

Depends on how much air you use. A random orbital sander will burn through 20 gallons in no time. A seldom used blowgun will not tax the setup. Just be aware under your plan the compressor will take a LONG time to fill the tank.

Figure out what you plan to do and then buy a compressor for those needs + a little extra for future needs. Price is just one part of the equation.
jurgen

widebody911 · widebody911's Garage

Yes, it would work; BTDT with a 1/4 diaphram compressor originally intended for airbrushing when the starter went out on my compressor and I was in the middle of painting a bus.

It's a factor of how long you're willing to wait, and will that poor little compressor survive the run time.

You could get an old propane tank - like the ones used to fuel a house - and turn that into your aux air tank. I've considered doing something similar, although my compressor is adequately-sized now, it would help out when I'm doing big jobs, like sanding or sandblasting.

RickM · RickM's Garage

A smaller compressor will not run air intensive tools like an impact wrench or larger sander. Sand blasting will pretty much be out of the question.
A larger compressor will not empty the tank if appropriately sized. The motor will kick on and top off the tank as you work when a certain (lower) pressure is achieved.
A smaller compressor will work harder, will take a long time to fill it's tank and introduce a lot moe moisture into the system.

That said I've used a 1 hp / 13 gallon Sears compressor for 21 years. Still going strong but with it's limitations.

Teutonics · Teutonics's Garage

As a reference point, my 6hp two-cylinder compressor with a 33 gallon tank has a hard time keeping up with an orbital sander... the compressor runs almost continuously.

RickM · RickM's Garage

However air tools can have different consumption rates. Some made specifically for lower CFM. Of course you'll lose power with the less demanding tools.

FastDave · 02:23 PM

Any reciprocating type air compressor (which means anything except rotary screw air compressors) with cast iron pump has an 80 percent duy cycle which means it needs to rest 3 minutes every 15 minutes. Any reciprocating type air compressor with an aluminum pump (which includes pumps with cast iron sleeves) has a 60 percent duty cycle which means it needs to rest 6 minutes every 15 minutes. People who exceed the duty cycles have problems with check valves (the part that cuts off the air from leaking out of the tank when the pump isn't pumping) and head valves. Both these components are made of spring steel and are affected by the intense heat created when exceeding duty cycles and/or recommended pressure limits. There is no way to match the air consumption of an air tool directly to the output capacity of an air compressor just by comparing the typical stats. Pressure settings on the regulator (not the pressure switch), air hose size, air fitting size, and air tool effeciency must all be taken into consideration. I'll be glad to tell you more if you need to know.

RickM · RickM's Garage

Good info, Dave. Thanks.

RoninLB · 11-18-2004, 04:34 PM

I find that 5hp, twin cyl, 60gal is borderline for air files, impact guns, etc

FastDave · 11-19-2004, 05:24 AM

A real man's 5 hp 60 gallon air compressor will put out about 12 cfm or more @ 90 psi which is sufficient for any 3/8"dr, 1/2"dr or 3/4"dr air impact wrench, but not a 1"dr air impact wrench. Most air sanders require a 2-stage air compressor to run the tool continuously. Sure, any air compressor that produces 90 psi will run most any air tool, the question is about duration.

RickM · RickM's Garage

This should do the trick

RoninLB · 11-19-2004, 06:27 AM

Quote:

Originally posted by FastDave

A real man's 5 hp 60 gallon air compressor

I got my 60gal from Snap-On. It was turned back to the dealer by a body shop who said it wasn't functioning. 1/2 price as is. Motor worked so I replaced the clogged air filter. Bingo.

RickM · RickM's Garage

Ron, who make the compressor fro Snap-on?

RoninLB · 11-19-2004, 06:47 AM

Quote:

Originally posted by RickM
Ron, who make the compressor fro Snap-on?

I just looked at it. It doesn't have the Snap-On logo. The detail plate says Brunner Eng & Mfg. It appears to be sourced from Ajax Corp in Rochester, NY.

Joeaksa · 11-19-2004, 08:05 AM

Worked with a old Sears unit for years, 3 hp and 20 gallon unit. Still works fine but when I got the glass/sand bead cabinet it ran all the time and had to take a lot of breaks to let it catch back up.

Went to Harbor Freight and got a 60 or 80 gallon monster 6.5 HP 230 volt unit that just digs right in and holds its own. 14+ cfm at 90 psi or so and cost only $380. Well worth it and now that I am using 230 to run the puppy my electrical costs are lower.

JoeA

FastDave · 11-19-2004, 10:00 AM

Quote:

I just looked at it. It doesn't have the Snap-On logo. The detail plate says Brunner Eng & Mfg. It appears to be sourced from Ajax Corp in Rochester, NY.

Ajax makes really good air compressors...sometimes hard to find parts, but still a good unit.
Did you get it for under $500? if I may ask...

FastDave · 11-19-2004, 10:01 AM

Quote:

Went to Harbor Freight and got a 60 or 80 gallon monster 6.5 HP 230 volt unit that just digs right in and holds its own. 14+ cfm at 90 psi or so and cost only $380. Well worth it and now that I am using 230 to run the puppy my electrical costs are lower.

Good luck with that! ha

Joeaksa · 11-19-2004, 10:09 AM

Dave,

Its worked and worked very well for the last 18 months. Ha yourself!

Joe A

FastDave · 11-19-2004, 12:16 PM

Quote:

Joeaksa

Joe,

Good luck with that!

Dave

RoninLB · 11-19-2004, 12:55 PM

Quote:

Originally posted by FastDave
Ajax makes really good air compressors...sometimes hard to find parts, but still a good unit.
Did you get it for under $500? if I may ask...

Thanks for that info..
I bought it around 1985. I don't remember how much. It was 1/2 of what the bodyshop paid for it the month before. Snap-On drives up with this unit jammed in his truck. "You want a small compressor?", "What's the story?", "blah blah blah".
Done deal.

He nor I knew what was wrong with it. It's also an upright 60gal which wasn't desirable at the time.. I think there was a saftey issue that was starting to be enforced on Long Island at the time which may explain why he was anxious to unload it. He just said that the unit was a big pia for him to deal with.