View Full Version : oilles compressor
10-24-2001, 07:53 PM
Not really a metalworking question but I thought someone here might have a suggestion. Have a Sears 5.5hp 25 gal. oilless compressor that isn't worth a damn. Takes forever to build up pressure and drives you crazy while doing it. Wondered about the feasibility of replacing the pump [and motor too I guess] with a oil lubricated model. Want to run die grinders, Impact wrench, air drills and the like without having to listen to this thing run constantly. Also, I don't get this horsepower thing. My unit says 5.5 hp. My dad has a 3hp motor on his tablesaw that you can't lift. I see pumps advertised in the different tool catalogs. Anybody got any ideas about this?
10-24-2001, 08:09 PM
There is a circular filter on the side of your compresser. It is small and clogs quickly, greatly decreasing preformance. You can reuse the tank by plumbing it into another system and then when you realy need it it will kick in and you will have two compressors handling the load. Check to see if you have water in the tank. It can cut tank capacity in short order in humid climes. Yea I don't get the HP thing shouldn't it cross with Watts but it doesn't.
10-24-2001, 10:57 PM
Horse power is a funciton of amps times Volts with 746 wats equal to 1 hp. What Sears does is, over load the motor. When that happens the voltage stays the same but the amps increase.Hp being the function of amps and volts the HP apparently increases. If you operate the motor this way very long it will over heat and evently will burn out.
For the most part a motor is not operated very long in this condition, and not much trouble occures. A table saw would be tool that could be operated overloaded for a period of time and the motor would heat up.
All this is,is a sales gimic to convince you that you are getting more for your money.
When you have some spare time and want an education in BS, ask a sales person in Sears, how do you get more HP out of a motor than the name plate states. I did it one time, the answers ranged from a govner in the motor to using electronics.
One way motors are made lighter is the use of aluminum wire as opposed to copper wire, and the frames are skeletionized,just look at the motor in the clothes dryer or washing machine, the motor on your compressor will not look this bad.
Hope I did not get to far off line.
10-24-2001, 11:23 PM
If you go to rebuild your rig, get a Cast Iron 2 stage 2 cylinder, use a good synthetic oil without detergents (not motor oil!) ISO-100 weight such as Amsoil "PCK" reciprocating compressor lubes. Buy a robust motor - 220V if you have it in your shop - 110V would require a 20A circuit and plug.
In Canada a nice cast iron compressor with a pulley/fan assembly is about $180 (canadian).
10-25-2001, 11:29 AM
I hear that Wal-mart chainges their compressers every year. Friend of mine got one for next to nothing.
Price it out before you start buying parts. You may find it's cheaper to buy a whole new compressor than to try to upgrade the pieces of your existing unit.
I went the replace-the-parts route on my compressor a couple of years ago, and by the time I bought a new motor, new pump, new pressure switch, re-did the plumbing, and assorted odds and ends, I seriously doubt that I saved any money, or at least hardly enough to justify all the work involved. If you can get some/all the required parts used, of course, then it might be a different story.
10-25-2001, 05:26 PM
Thanks for all the info and advice. Think I'll probably just buy a new compressor. The pumps I looked at cost as much as I paid for the Sears unit. Should have researched these oilless jobs more before I bought one.
10-25-2001, 07:48 PM
This should get you a little upset. While driving down the street the other day I ran across a guy cleaning out his garage and barn. He had a compressor and a bunch of other stuff out by the curb for the trash man to pick up. The wheels were gone and it looked like it had been sitting for several years. I picked it up, brought it home, blew off the dust, added a fresh cord and it worked just fine!
Also in the pile was a plastic box that I also brought home to use to put some tools in. When I opened it up there was a brand new spray gun inside with the receipt from Sam's for $65!
Amazing what some people will throw out.
10-25-2001, 09:46 PM
I have always found the parts route gives a far superior machine. It is important to get a CAST IRON compressor. The so-called oil-less compressor made of plastic and Aluminum are cheap for a reason - they are crap compared to good old Cast Iron.
And, in twenty years when it dies you can rebuild it for $50 (if you used good oil in the first place).
10-27-2001, 07:06 PM
Compressors is something i know about. Thrud is on the right page. Get away from Oilless compressors. One thing that everyone missed is that they are REALY LOUD! Also the size of the line common out of the compressor tank will affect your the cfm getting to your tools. A 1/4" line con only flow so many cfm. A 3/8" line is usually good enough for most air tools.
I mentioned cfm. Cubic Feet per Minute. Air tools are rated according to pressure and cfm. A typical air impact gun uses about 9.0 cfm at 90 psi. These ratings are very important when buying a compressor. Look for a cast iron, 2 stage, 5 or more horse on 220 volts with a rating of 11 to 13 cfm at 90 psi with a 40 or more gal. tank. That should be good enough to do anything you want. Even light sandblasting. Email me if you want to know how to build a cheap sandblaster. 100.00 Canadian. Not bad eh!
Hope that helps Spkrman