air compressor

[n3833v]

I bought one just like Bruces for 105.00 in a hock shop. It's great for about everything. It is so portable that I use it for more than the plane.

John

[canderson]

I did end up buying the current version of the one Bruce shows. Mine has 150psi and was well under $200. Works like a charm. It didn't come with any nailing equipment, but did have the right accesories for use right out of the box. There are several choices in this price range at Lowes or Home Depot. Thanks again for the advice.

[GAHorn]

Great buys on air compressors provokes me to share my joy on acquiring my shop compressor. It was at the local big-box store standing in the automotive section and offered for the "discount" price of $579 (ordinarily $749 they said). After a month no one had bit on the deal and the dept. mgr wanted it out of the way for a new display.
I told him if he'd deliver it out to the ranch I'd consider it, but said so only as a joke. He surprised me and said, not only would he deliver it, but he'd knock 50% off!
He did even better than that.... he sold it to me for $250 even (he said because it was a 230-volt unit that none of his regular customers wanted.)
It's exactly what I wanted and I'm glad to have it. (Like Tim Allen.... ROAR ROAR ROAR.)


60 gal tank, 6 hp motor 135 psi/10.2-11.5 cu.fpm
Won't fit in the trunk, tho'. (and you need to bolt it to the foundation or tie it to the wall so these types don't ever fall over....they're top-heavy and dangerous if they fall.)

[Chris Christensen]

There is another option, which I use in the hanger.
It is a 15 lb. bottle of C02.
I also have a 5lb bottle that goes with my old 77 IH Scout into the 4x4 backcountry
Google POWERTANK http://www.powertank.com/
NO voltage needed, just a welding supply shop for occasional refills.
Also a LOT quieter !

[mbram]

I bought a 2hp twin tank (4gal) at the import tool store for $89.00 and T in my 10 portable tank for additional capacity
I am running the hangar power on a 13 hp gas generator (think green acres circuit 1+2 or 3. Increase compressor size no lights).

[GAHorn]

I bought a 2hp twin tank (4gal) at the import tool store for $89.00 and T in my 10 portable tank for additional capacity
I am running the hangar power on a 13 hp gas generator (think green acres circuit 1+2 or 3. Increase compressor size no lights).

That's a clever solution. A person can buy a smaller capacity, less expensive compressor system then, using a flexible rubber hose connection to the small system to connect a portable tank to it, can increase capacity for short-term useage projects ,... and still have a portable tank for convenience purposes.

[blueldr]

George,
Are you sure that's a six horse power motor on that vertical compressor of yours, or is it rated a six horse power compressor?
A six horse power motor is usually pretty darn large and requires an awful lot of power, doesn't it? How many amps does it pull under load?

[GAHorn]

The decal claims 6 hp on the unit assembly. The actual elect. motor datatag says :
HP- Spl
Volts - 240
Amps - 15

One hp equals 746 watts. So the math 240 X 15 = 3600 divided by 746 = 4.8 hp.
Of course there is a pulley/sheave on that motor about 2" dia., driving one on the compressor about 10" in diameter so some degree of change in actual power transmittal might exist.

The 6hp rating on the unit is a bit more confusing. My "Machinery's Handbook" (1948) has some rather intimidating formulas for determing hp to compress air, and some charts for "horsepower equivalents" for "adiabatic and/or isothermic" compression of air "at one-atmosphere" (and lots of other qualifying statements). The charts are further broken down into single/double/triple stage compressors. Mine is a single stage, cast iron, twin-cylinder pump.
Additionally, the charts address 1 cu. ft. of air per min, and mine is a 60 gallon tank, so how all that figures into the scheme of things begins to look like a political contest between a war-hero, an ex-wife, and a member of the Gary, Indiana yacht-club. Perhaps Miles can provide a solution to your question, BluElder!

[blueldr]

Come on, Miles. Speak up!

[cessna170bdriver]

Sound like Dick understands the difference between a motor that is "rated" for a particular horsepower and one that will actually produce that horsepower.

I actually work more with electronics than electrical power, and I'm afraid of anything over 28 volts, but I'll give it a shot at explaining it:

George is right in that 15 amps at 240 volts represents 4.8 horsepower. However that is INPUT power. Since no motor is 100% efficient, the OUTPUT power will be less; by how much I haven't a clue. If you really want to know, put a torque meter and tachometer on the output shaft and do the math.

I'm not sure how they get away with rating the motor at 6HP, but it's most likely a marketing ploy. I've done the math on some data plates and discovered that they rate the horsepower by multiplying "starting current" by the "running" voltage. All AC motors draw more current during starting than they do running, so this jacks up the "rated" HP. (This make no technical sense at all, as they are essentially taking current and voltage from different points on the power curve.) If George's motor draws about 19 amps on startup, this might explain his "rating".

George is also correct in that gearing via the pulley sizes can affect the amount of power transmitted (or more correctly "transmittable") by the motor to the compressor, but this is just to match the relatively low torque available from the motor to the higher torque requirement of the compressor. You woluld NEVER be able to pump a "real" 6HP worth of air with a "real" 4.8 HP motor regardless of the gearing. The first law of thermodynamics says you can't get something for nothing. (Unfortunately, the second law says you can't even break even...)

Miles

[GAHorn]

In what appears to be an identical unit (they've changed the model number but they look exactly the same) Campbell Hausfeld offers what they state is a 3 "running" HP unit. I'll bet they are the exact same unit and they've corrected their claims under some "truth-in-marketing" requirement.


http://www.chpower.com/webapp/wcs/store ... 646_10689_

[blueldr]

I guess that this discussion really boils down to the fact that despite what Continental and Lycoming feel is a necessary compressor size, the vast majority of compression checks performed over the years have been done with much smaller units, and probably continue to be so done.

[steve grewing]

My "portable" air compressor is an old cast iron one-lunger out of a commercial washing machine that used pneumatic control valves. I made a reservoir out of three inch PVC about one foot long. It takes about two minutes to build 100 PSI but is works fine for doing compression checks, airing up tires, etc. For when I have big tasks I plug in the additional reservoir of the same size in line with the hose. Hi-tech. As Chris stated about portable CO2, we have a portable nitrogen bottle regulator setup with a quick disconnect which works well when we have to go out on the ramp too far to run an air-hose.
If memory serves, the inefficiencies in an electric motor is the problem, with resistance, heat generation, EMF, etc. dragging it down. The general rule was 746 watt output required approximately 1000 watts input. It seems like my "machinerys handbook" has that info but it's not quite as old as Georges copy. I suspect todays motors are more efficient.

Steve

[GAHorn]

. It seems like my "machinerys handbook" has that info but it's not quite as old as Georges copy. ...
Steve

Mine was requisitioned from my Dad before he died. He bought it after the war when he attended the Univ. of Houston studying elect. engineering. The University bookstore price-tag inside the cover says $8. (used editions presently sell for as much as $60 and new ones list at $159)

I get a little melancholy when I use his stuff these days.

[canderson]

I guess that this discussion really boils down to the fact that despite what Continental and Lycoming feel is a necessary compressor size, the vast majority of compression checks performed over the years have been done with much smaller units, and probably continue to be so done.

And here I was thinking this was such a benign topic. Just comes down to squeezing a certain amount of air to meet your needs. Interesting anecdotes- thanks.

Nice big tank, George!