How do oilless compressors last as long as they do?

[SteveD2]

First - I know there is a compressor section here but nobody ever looks in there.

I have a 2hp oilless compressor in my garage and the thing works pretty good. I frequently have it running continously for 10 minutes or more and the **** thing just keeps on kickin'. How the heck do they last as long as they do? What makes an oilless different from one with oil? I mean they both have a cylinder/piston in 'em...

 

[JohnBrowning]

I agree. I painted my SUV with a 5 HP oil less. I am guessing that they use a turbine instead of a piston so itis eaiser to lube it for life. I can not say for sure. I have woundered this as well.

 

[tundra30]

Most oilless compressors I know of are powered by electricity, therefore you don't have the heat or nasty byproducts generated by combustion. With a good oil in there and the right design, there would not be any reason to change the oil.
I wonder if one day we will be driving vehicles will electric powered oil-less engines?

[ January 22, 2004, 11:01 PM: Message edited by: tundra30 ]

 

[SteveD2]

quote:

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Originally posted by tundra30:
Most oilless compressors I know of are powered by electricity, therefore you don't have the heat or nasty byproducts generated by combustion. With a good oil in there and the right design, there would not be any reason to change the oil.
I wonder if one day we will be driving vehicles will electric powered oil-less engines?

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Does it have oil at all though? I don't think there is any in there, changeable or not. On a normal air compressor designed like a small engine the oil is suppost to be changed like every 25 hours isn't it? There is no combustion in there either...

 

[Bret Chase]

most oiless compressors use a teflon seal on their piston. there is no oil in it's crank case. the trade off is the service life of the tool... oiless compressors typically last no where near as long as a traditional piston compressor.

-Bret

 

[SteveD2]

Why don't standard compressors use a teflon seal? I would think if they last as long as they do without oil they would last **** near forever with oil...

 

[tom slick]

quote:

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I agree. I painted my SUV with a 5 HP oil less. I am guessing that they use a turbine instead of a piston so itis eaiser to lube it for life. I can not say for sure. I have woundered this as well.

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no turbine, they still have pistons. turbines (actually called an impeller or compressor) can provide lots of CFM but not much pressure. if they did have turbines they would sound like a jet engine, not like a hyper lawn mower. the oiless compressor i have had apart had a graphite type material sealing the piston and it didn't have rings like a automotive piston, more like large blocks surrounding the piston.

 

[jsharp]

quote:

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Originally posted by ZmOz:
Why don't standard compressors use a teflon seal? I would think if they last as long as they do without oil they would last **** near forever with oil...

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The temperatures are too high for teflon seals in a normal compressor thanks to their higher compression ratio. Temps are high enough in fact that you'll see carbon deposits in the cylinder heads if there is any oil present in the output air.

The only sealing method in piston type pumps that has been shown to work long term are common piston rings, just like an IC engine. The valves are another story. There have been many ingenious ways to build these valves over the years but again, because of the temperatures involved, they are all metal to metal seals...

 

[satterfi]

Take it apart and you might not be so impressed.

A good cleaning and regreasing the internals wouldn't hurt it either.

quote:

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Originally posted by ZmOz:
First - I know there is a compressor section here but nobody ever looks in there.

I have a 2hp oilless compressor in my garage and the thing works pretty good. I frequently have it running continously for 10 minutes or more and the **** thing just keeps on kickin'. How the heck do they last as long as they do? What makes an oilless different from one with oil? I mean they both have a cylinder/piston in 'em...

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[garyb80]

I have an oiless Craftsman compressor and the piston is made from Ultra High Density Polyethelene (UHDPE). UDHPE is claimed to be 10X more wear resistant than mild steel in an unlubricated sliding friction application. It also has a low friction coefficient so the motor doesn't have to work as hard.

 

[rpn453]

We require dry, oil-free air for our instruments and valve actuators at a power plant, and we have a couple of 50HP piston-driven oil-less compressors still running that have probably been in service for at least 25 years (with rebuilds of course). These run 24 hours a day and are water-cooled. I'm not sure how long the rings last though. They’re only a very small part of our air supply, but they’re still working so we’ll probably use them until it’s not worth it to repair them. They are being phased out by the more reliable rotary screw design, in which there is no oil required because of tight clearances and no metal-to-metal contact. Here’s an excerpt from the technical service manual:

“At the top of each crosshead guide is a wiper gland assembly preventing oil from rising into the cylinder block. Each piston is fitted with segmented carbon rings, internal spring rings and a solid guide ring. The carbon rings in conjunction with iron alloy cylinders obviate the need for cylinder lubrication thus ensuring that the delivered air is completely free from oil contamination. As a further safeguard against oil laden air reaching the pistons, it is essential that no oil or grease be allowed in the cylinders, since this will cause damage to the carbon rings.” – Broomwade, 1967

Wear will be much higher in an oil-less design, but they’re cheaper and many people wouldn’t use a compressor at home enough to wear it out anyway.

[ January 23, 2004, 02:59 PM: Message edited by: rpn453 ]

 

[Shannow]

For some reason at work, there's been a trend for people putting in new plant to put in a stand alone oil free compressor, rather than connecting to the reticulated system (we've got 3500 spare CFM sitting there most days).

The oil free compressors don't appear to last very long at all when we run them all day every day.

They last even less long when a diligent fitter notices the sump is empty and fills it.

 

[rpn453]

quote:

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Originally posted by Shannow:
we've got 3500 spare CFM sitting there most days

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Send some air my way! We definitely don't have that problem. We're lucky to hit 80psi with our collection of 12 little compressors. Our biggest are 490 cfm.

 

[Shannow]

The two power station compressors are Atlas Oil Free 1800CFM water cooled, we've got two Broomwade VM750 piston types, and recently installed an Atlas oil flooded 1000cfm air cooled. (The 1000cfm compressor itself costs equivalent to an overhaul on an oil free unit)

The multiple compressor designs are there to reduce the risk of tripping (our sister station has discovered the evils of having all the same kit, when a type fault develops.

The pneumatic ash handling system has it's own 3 off 1000cfm compressors but isn't connected to the station.

 

[tom slick]

at my "normal" job the plant runs on 2 rotary screw compressors. they are 284 cfm at 150psi, they have their own thermal mass driers built into them. they even tell you when to change the filters and oil!

i don't think the average backyard mechanic is going to wear out an oilless compressor unless it is undersized for what they are doing. just remember to check to make sure the CFM of the compressor exceeds the max CFM of the tools you are going to use it with.

 

[mrchecker]

My oilless compressor (Campbell-Hausfield) has sealed bearings on the crank and rod, and uses a rubber diaphragm on the piston. Stroke is about 1 inch. It was cheap, and since I only use it a couple times a month it should last quite a while while needing no maintenance other than draining the tank now and then.