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  #16 (permalink)  
Old 12-23-2009, 01:38 PM
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Not exactly the deal of the year. And not very confidence-inspiring. But, hey, the shipping is free! lol
Not really unusual, though. The Quincy offers a 2 year limited warranty. If you buy their startup kit, they extend the warranty on the pump to 5 years limited.

I think the issue here is that they want to be sure you start it up with synthetic compressor oil and you'd have to buy the oil/filters anyway.

So you're paying $400 for an extra 3 years warranty on the pump, the fact that it's made in the U.S., and perhaps a somewhat lower average maintenence cost (though no data is available to prove this.)

Again, my point is that for $1300, I rather blast with the IR compressor and a refrigerated air dryer than the Quincy and a $20 water trap.

If money is no object, then by all means, go nuts.

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Old 12-23-2009, 02:08 PM
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Originally Posted by wyomingclimber
If money is no object, then by all means, go nuts.
Ain't it the truth!

My little 1986 Craftsman 1-1/2 HP compressor only had a 1 year warranty on it. Changed air filters and done oil changes, replaced the pressure switch and 1 belt, so far. Prolly average durability, but I have used it a LOT- being that it's portable.
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Old 12-23-2009, 02:40 PM
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Originally Posted by wyomingclimber
Oldred: I'm not sure it's as bad as you think.

Actually in spite of how it sounded I don't think it is necessarily a bad outfit, just badly mis-represented, and overall it probably is a decent compressor for it's size.


I probably came on a bit strong about it but that particular one is kind of a special case, I said it was a rip-off not so much because I think it is a bad outfit but because of the dishonest ratings. 18.1 CFM@90 PSI for that pump/motor combo is simply so far off the mark it borders on fraud and with so much exaggeration about compressor specs from the manufacturers it kind of gripes me when I see it from an otherwise reputable outfit like IR. Before they came up with those figures they tried a little scam called "tank assisted CFM" but apparently no one would fall for that one and they dropped it after a short time, 18.1 CFM may be the pump displacement or some other gimmick but there is simply no way that single stage pump can put out that kind of CFM with only 5 HP. The plus for that compressor is that the 5 HP rating is honest enough and the pump looks to be a fairly robust unit but I think that's the worst part about the less-than-honest specs, they would have looked darn good for a compressor of that size if they had of just told the truth! 14 CFM for a single stage pump powered by 5 HP would be more than respectable but for some reason someone must have decided it should be dressed up a little more. Also for a compressor in that price range they certainly could do better than that light Emerson motor, heck even Harbor Freight uses a Baldor on some of it's U.S. General brand models that cost less than the IR! That motor burn out problem unfortunately is real too but hopefully it was just a run of bad motors that they might have gotten sorted out.
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Old 12-25-2009, 05:35 AM
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Originally Posted by wyomingclimber
Oldred:

Acknowledging that you've forgotten more about this subject than I'll ever know, I own this compressor and I'm not sure it's as bad as you think.

I raced it against a Harbor Freight compressor rated at around the same CFM and found it to be about twice as fast at filling a tank. With a 1/8" sandblaster tip, this thing will hold 90psi forever. Maybe it is 14cfm, but as a practical matter, I can't find a way to outrun it.

I haven't had any problems with durablility, though that's not saying I wont. As I recall, if you use the IR startup kit, it has a pretty good warranty. Running it constant in nasty conditions for around 6 hours a day for a few weeks doesn't seem to bother it.

I know there is a lot of bias against Chinese stuff on this board, but I wouldn't say that a Made In America sticker assures quality any more than a Made In China sticker assures junk.

The point I was trying to make is that if you have a budget of $XX, be sure you balance the quality of all the parts of that system--electrical/compressor/dryer/etc. If you've got the dough, absolutely go Quincy.

No. Wait. Actually, my point was "for God's sake take it to a professional and pick it up done a week later!"

I'm still cleaning alum. oxide out of my ears and the **** got into my wallet and ruined all my credit cards. Oh, and it got into my shoes and ruined all my socks! Oh and...
Yes that was discussed thouroughly in thread Respectable paint on 120V compressor?. Post 42 and 43 are the proof in the pudding.
The old know it all never posted again in that thread once you posted your results.,
He obviously has a **** ** for IR, and anyone that does not agree with him.


I too have the same IR and have had excellent results with it.

Last edited by 302 Z28; 12-26-2009 at 05:25 PM. Reason: Violation of guidelines. Please see: general board guidelines.
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Old 12-25-2009, 08:52 AM
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I completely forgot about that.

Man, I have too much time on my hands
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Old 12-25-2009, 10:30 AM
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Originally Posted by Old Fool
Yes that was discussed thouroughly in thread Respectable paint on 120V compressor?. Post 42 and 43 are the proof in the pudding.



You picked out what you wanted from that other post to try to make your point but go back and look at everything I said about that thing before calling me names. I already admitted in this very thread that I came on too strong about it in my first reply to this thread and I clarified that I meant it was, as I said, a "rip-off" because of exaggerated claims and not that it was necessarily a bad compressor. I have said repeatedly that it was a decent outfit and have told more than one they would be happy with it BUT I also said it is not all they claim it to be and if that hurts your feelings that's too bad.

Last edited by oldred; 12-27-2009 at 11:38 AM. Reason: I felt the deleted text was just venting against a percieved personal attack and offered nothing technical pertaining to the subject being discussed
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Old 12-25-2009, 10:37 AM
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Originally Posted by Old Fool
I too have the same IR and have had excellent results with it.

He obviously has a **** ** for IR, and anyone that does not agree with him

Ok maybe I am just making up all that stuff and maybe these 4 guys in this SAME thread are just being know it all's too?

http://www.hotrodders.com/forum/comp...=emerson+motor


Plus I got a call about 3 months ago about one here locally that has the same problem and I have seen this at least twice on other sites, but then I guess the "old know it all" should not tell anyone to keep from hurting feelings!

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Old 12-25-2009, 02:02 PM
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Sorry guys, but any claims that a 2 stage compressor is "more efficient" than a single stage of similar construction is purely a myth.

2 compressors with equal hp, running at the same speed, similar pump construction but one being single stage and the other two stage, the single stage will put out more CFM every time.

The reason is real simple. In a 2 cyl compressor, for example, you have 2 cylinders pumping air to the tank with a single stage, and one cylinder pumping to the tank in a 2 stage, while the 2nd cylinder is just pumping to the cylinder that's actually supplying the tank.

If you want to get an idea of which compressor is most efficient, check the discharge temperature of the air coming from the single and 2 stage units. The 2 stage will always have the higher discharge temperature. Heat rejection is the most common and most accurate method of measuring wasted work. Higher discharge temp = more wasted work = less efficiency.

Simple reason for this as well. The 2 stage runs the same quantity of air thru 2 compression cycles. Each cycle represents work input to the air. Some of the work is stored as potential energy in the form of compressed air, while the rest is converted to heat, either carried in the air or rejected thru the compressor casting, piping, intercooler piping, etc. Take a specific volume of air and compress it once, and you'll have some discharge temperature. Now run that same chunk of air thru a 2nd compression cycle, and it'll get hotter every time. Each compression stroke represents a combination of useful and wasted work, so when you compress the same air twice you will always be adding the wasted work to that air as well as the useful work. Compress it once and push it to the tank, as in the case of a single stage, and you've added less heat, and less wasted work, to that volume of air.

For most uses, whether its a body and paint shop, or a machine and fab shop like my shop, a single stage compressor will do anything that needs to be done via air, and it'll do it cheaper both on a monthy operating cost and on a long term maintenance cost, because the single stage will typically be operated at a lower temperature and lower level of mechanical load. For some reason though, there's been such an effective job of selling people on the need for 2 stage compressors that its difficult to even find large cast iron single stage pumps today.

We've got 3 compressors at our shop. One is a 5hp 2 stage IR, made before the US discovered manufacturing in China, which we've always run at a cutout pressure of 175-180 psi. Because my dad has been in the heavy equipment business for about half a century, the pressure is set that high so it doesn't take half a day to fill a big tire to 120 psi. Its piped into the shop air system, but valved off from that system unless we happen to need it for something unusual.

The 2nd compressor is a Quincy single stage made in the mid 50's. 2 cyl pump, rated for use with a 5, 7.5, or 10hp motor. Its got a 3hp single phase 1750 motor on it because it was originally bought for use in a state highway maintenance garage in a remote mountain location where the only electrical service into the building was a 100 amp single phase.

The third is a 2 stage 10hp 3 cylinder radial. Its the one that's normally used for general shop air supply. We normally keep it set for 140 cutout and 105 cut in pressures.

The 10 went down one day when I was bead blasting a bunch of parts. I opened the valve and started the 5hp IR. Found it couldn't quite keep up with the blaster. Almost, but not quite. So I started the 3hp Quincy as well, and finished the job.

Then, out of curiosity, I tried the IR, and then the Quincy, separately, just to get some idea of how much air each was putting out. Nothing else using air at the time. Laid a chunk of steel on the blaster's pedal and let each one run until their pressure was no longer dropping. IOW, would one hold a continuous 35psi and the other a continuous 70psi, or whatever, since it would give some reasonable measure of the output of each.

The IR ran a while and eventually settled out at 66psi. Then the Quincy settled at 62psi. Very little difference in output, since both were discharging thru the same orifice and both pressures were measured with the same gauge.

Remember though, the Quincy is only 3hp while the IR is 5hp. Two things going on here to make their performance so nearly the same. One was the inherent better efficiency of a single stage, primarily due to less work being wasted as heat. The other is that the slow running speed of the Quincy made its pumping efficiency even higher than normal via reduced intake pressure losses, and even less than normal heat input into the air due to the reduced speed necessary for it to play nice with the 3 hp motor.

Obviously, if you have a need for high pressure air, the single stage isn't the way to go. OTOH, its real difficult to find any sort of tool or other air operated device that's designed for an operating pressure greater than 90psi. Personally, if I ran across someone who had a quality 10hp single stage in good shape, and they had a need for a 2 stage, I'd swap 'em my 10 horse in a heartbeat.

Regarding the 5hp IR single stage mentioned above, the 18 cfm is a very rational output number. 4 cfm per horsepower isn't unusual at all for a single stage. Dad's got a number of portable compressors from small to pretty big, all with CFM measured at 90psi output. Little 100 cfm jobs, driven by a 25hp diesel, up to a 1600cfm driven by a 400hp diesel. Right across the board, even though the collection is made up of several brands, the CFM number is right around 4x the engine horsepower number.
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Old 12-25-2009, 03:44 PM
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Old 12-25-2009, 04:44 PM
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Originally Posted by TubeTek
Sorry guys, but any claims that a 2 stage compressor is "more efficient" than a single stage of similar construction is purely a myth.

2 compressors with equal hp, running at the same speed, similar pump construction but one being single stage and the other two stage, the single stage will put out more CFM every time.

The reason is real simple. In a 2 cyl compressor, for example, you have 2 cylinders pumping air to the tank with a single stage, and one cylinder pumping to the tank in a 2 stage, while the 2nd cylinder is just pumping to the cylinder that's actually supplying the tank.



Simple reason for this as well. The 2 stage runs the same quantity of air thru 2 compression cycles. Each cycle represents work input to the air. Some of the work is stored as potential energy in the form of compressed air, while the rest is converted to heat, either carried in the air or rejected thru the compressor casting, piping, intercooler piping, etc. Take a specific volume of air and compress it once, and you'll have some discharge temperature. Now run that same chunk of air thru a 2nd compression cycle, and it'll get hotter every time. Each compression stroke represents a combination of useful and wasted work, so when you compress the same air twice you will always be adding the wasted work to that air as well as the useful work. Compress it once and push it to the tank, as in the case of a single stage, and you've added less heat, and less wasted work, to that volume of air.

For most uses, whether its a body and paint shop, or a machine and fab shop like my shop, a single stage compressor will do anything that needs to be done via air, and it'll do it cheaper both on a monthy operating cost and on a long term maintenance cost, because the single stage will typically be operated at a lower temperature and lower level of mechanical load. For some reason though, there's been such an effective job of selling people on the need for 2 stage compressors that its difficult to even find large cast iron single stage pumps today.



Then, out of curiosity, I tried the IR, and then the Quincy, separately, just to get some idea of how much air each was putting out. Nothing else using air at the time. Laid a chunk of steel on the blaster's pedal and let each one run until their pressure was no longer dropping. IOW, would one hold a continuous 35psi and the other a continuous 70psi, or whatever, since it would give some reasonable measure of the output of each.

One was the inherent better efficiency of a single stage, primarily due to less work being wasted as heat.

I don't think I have ever seen so much mis-information so eloquently put, you write very well!

Tube with all due respect you got almost nothing right and the reason is simple, pump efficiency.

[2 compressors with equal hp, running at the same speed, similar pump construction but one being single stage and the other two stage, the single stage will put out more CFM every time.]

That logic is totally flawed because it assumes both compressor pumps are the same displacement for a given HP and are running at the same speed which is almost never the case and a 5 HP two stage will produce more CFM per HP than a 5 HP single stage. The statement that the single stage is more efficient is just plain wrong, the two stage is much more efficient than a single stage and because of this two stage compressors are able to use a larger CFM pump arrangement than a single for a given HP. What you are saying sure is going to come as a surprise to a lot of engineers out there that have had it wrong all these years! Your intentions are obvious and I am probably wasting my time but I will try to explain why the two stage has an efficiency advantage over the single stage.


First the single stage pump is a lot simpler and cheaper to build with a heck of a lot fewer parts and as you did correctly say they are quite sufficient for most small shops. This simplicity and cost effectiveness comes at the expense of efficiency however because the single stage must make a major compromise between peak pressure and recovery time, besides it would run into heat problems above about 135 PSI without the benefit of the two stage inter-stage cooler. With a single stage pump and a given HP you can have high CFM or high pressure but you can not have both high CFM and High pressure at the same time, if you use a large displacement pump to produce high volume at low tank pressures you would exceed your HP limit before reaching the desired shut-off pressure. By using a smaller pump a higher peak pressure could be attained but at lower pressures the CFM would be low and the motor just loafing along. The compromise must be made then for the HP available between CFM at lower pressure and peak pressure. An example I have given in the past is a car with only one gear, you could have high torque and low top speed or high top speed but low torque or a compromise could be made between the two to make the most of the available HP. The two stage gets around this to a certain degree by using the small and large piston arrangement which allows for higher CFM at higher pressures but because the compression load is spread out it can do this while still reaching a higher peak pressure.


"The reason is real simple. In a 2 cyl compressor, for example, you have 2 cylinders pumping air to the tank with a single stage, and one cylinder pumping to the tank in a 2 stage, while the 2nd cylinder is just pumping to the cylinder that's actually supplying the tank."


You seem to be saying that as if it means nothing, maybe the engineers who designed these things are just stupid?

That is the very reason a two stage works so much more efficiently, by spreading out the load. If your reasoning were true there would be little need for two stage pumps with their extra complexity and expense. Trying to argue that the only reason for two stage pumps is the higher peak pressure of the usual 175 PSI would make no sense at all because not all of them go that high, some choose to pump more CFM at a lower pressure. Don't know where you got your info but you need to go back to school.

Last edited by oldred; 12-25-2009 at 06:31 PM.
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  #26 (permalink)  
Old 12-25-2009, 04:44 PM
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Old 12-25-2009, 09:38 PM
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Oldred:

Regarding efficiency. If you compare a single stage and two stage compressor that pulls 30 amps, it doesn't appear that the two stage flows more air @90psi.

So are you saying the efficiencies accrue at higher pressures? And if so, does this matter if you never use more than 90psi? (i.e. a car with only one gear is fine if the roads are so bad you can only drive 10mph.)

TubeTek makes an interesting point regarding thermodynamic law. Energy cannot be lost--put in 30 amps of electricity and you get 30 amps worth of air, vibration, and heat, right? That means a more efficient compressor would have to produce less of one or both of those unwanted byproducts.

I've never been able to wrap my mind around why two stage compressors are better. Having said, that, there are a lot of things I can't wrap my mind around
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Old 12-26-2009, 01:42 AM
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Originally Posted by oldred
I don't think I have ever seen so much mis-information so eloquently put, you write very well!

Tube with all due respect you got almost nothing right and the reason is simple, pump efficiency.

[2 compressors with equal hp, running at the same speed, similar pump construction but one being single stage and the other two stage, the single stage will put out more CFM every time.]

That logic is totally flawed because it assumes both compressor pumps are the same displacement for a given HP and are running at the same speed which is almost never the case
Not true at all. Nothing I said would constrain both compressors to have the same displacement. In fact, the typical single stage compressor will most always have greater displacement than a 2 stage designed for the same horsepower.

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and a 5 HP two stage will produce more CFM per HP than a 5 HP single stage.
Real world numbers don't show this statement to be true. Comparing IR's current 10hp single and 2 stage offerings (to get into compressors larger than any homeowner type units and the BS performance specs that often come with them) shows the single stage produces 36cfm @ 100psi, and 33.8cfm@125 psi. The 2 stage version produces 34.2cfm when ordered in the 125psi configuration. All measurements based on free air delivery. If both units were operating at 105/125 cut in and cut out, the difference in air delivery would be difficult if not impossible to measure by commonly available methods.

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The statement that the single stage is more efficient is just plain wrong, the two stage is much more efficient than a single stage and because of this two stage compressors are able to use a larger CFM pump arrangement than a single for a given HP.
What, specifically, make the 2 stage pump more efficient?

Quote:
Your intentions are obvious and I am probably wasting my time but I will try to explain why the two stage has an efficiency advantage over the single stage.
Not sure what sort of subversive intentions you might think I have, but I'm all ears and waiting for a logical explanation of this efficiency advantage, based on solid engineering principles. Since I got my degree in Mechanical Engineering from NC State a bit more than 36 years ago, I'm reasonably qualified to recognize the difference in an explanation based on engineering facts and one based on **** written by marketing type idiots that's typical of about 99% of the technical "facts" published today in reference to a wide range of equipment.

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First the single stage pump is a lot simpler and cheaper to build with a heck of a lot fewer parts and as you did correctly say they are quite sufficient for most small shops.
When built to equal quality standards, there should be very minimal difference in the cost of manufacture of a single stage or 2 stage pump of a given hp rating. There's few additional parts in the 2 stage, and the cost of manufacture of those parts would be partially offset by the fact that the displacement of the 2 stage will be consistently less than that of the single stage. Less total displacement = smaller components = reduced cost of manufacture.

In a 2 stage pump, we're not talking about some device that needs powder metal 4340 rods or hypereutectic pistons to survive, but rather one that operates at max pressures not much greater than cylinder pressures in a cranking but not running gas engine. When garden variety materials will get the job done, the smaller of 2 similar devices will almost always be cheaper to produce.

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This simplicity and cost effectiveness comes at the expense of efficiency however because the single stage must make a major compromise between peak pressure and recovery time, besides it would run into heat problems above about 135 PSI without the benefit of the two stage inter-stage cooler.
I stated clearly that I was excluding any application that actually needs air pressures in the upper range of pressures achievable only by a 2 stage pump. And so far, what you're talking about is "fitness for purpose" and not efficiency.

Quote:
With a single stage pump and a given HP you can have high CFM or high pressure but you can not have both high CFM and High pressure at the same time, if you use a large displacement pump to produce high volume at low tank pressures you would exceed your HP limit before reaching the desired shut-off pressure. By using a smaller pump a higher peak pressure could be attained but at lower pressures the CFM would be low and the motor just loafing along. The compromise must be made then for the HP available between CFM at lower pressure and peak pressure. An example I have given in the past is a car with only one gear, you could have high torque and low top speed or high top speed but low torque or a compromise could be made between the two to make the most of the available HP. The two stage gets around this to a certain degree by using the small and large piston arrangement which allows for higher CFM at higher pressures but because the compression load is spread out it can do this while still reaching a higher peak pressure.
You're still discussing fitness for purpose, and not efficiency. You've selected the ability to produce high pressure as a criteria for acceptable performance when, in fact, that high pressure is seldom if ever needed in any normal shop application.

Quote:
You seem to be saying that as if it means nothing, maybe the engineers who designed these things are just stupid?
And you seem to be dreaming up things I never said. Still waiting for that expalnation of increased efficiency.

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That is the very reason a two stage works so much more efficiently, by spreading out the load.
Not true by any stretch of the imagination. Spreading out the load, as you call it, enables the pump to reach a higher pressure. It does not make the pumping operation more efficient. Simple example.... I can't lift a 300# load 6 ft in the air by lifting it straight up. But I can roll it up an inclined ramp until its raised 6 ft with no problem. Does the ramp make the operation more efficient? No, it only provides a means of mechanical advantage. Technically, the process becomes less efficient when the ramp is used because rolling the load requires the effort necessary to overcome the rolling friction as well as the effort required to raise the load. The longer and more gentle the ramp angle, the more inefficient the operation becomes due to friction losses, even though the effort input within a particular expanse of time might be less. Similarly, the more spread out the load to enable compressing air to higher pressures, the less efficient the overall operation becomes due to increased frictional losses. Actual numbers from manufacturers on single and 2 stage compressors bears this out so long as both are operating within the acceptable pressure range of single stage compressors.

Quote:
If your reasoning were true there would be little need for two stage pumps with their extra complexity and expense. Trying to argue that the only reason for two stage pumps is the higher peak pressure of the usual 175 PSI would make no sense at all because not all of them go that high, some choose to pump more CFM at a lower pressure.
Still waiting for that explanation of enhanced efficiency. Lacking that, there are plenty of applications that use higher pressure air available only from multi-stage compressors. But, when you can look up the delivery specs on any legitimately rated and comparable single stage and 2 stage compressor, and see that the single stage will typically produce slightly more free air in the 100 psi range, why would you want to spend the additional money on the 2 stage if you don't need tank pressures higher than 125-130 psi?

Quote:
Don't know where you got your info but you need to go back to school.
Been there already. Didn't particularly care for it, but I ground thru to the finish. Maybe that's why I know the definition of efficiency while you obviously don't.

FWIW, a person can go to any number of sites, manufacturer and otherwise, and find claims that 2 stage compressors are more efficent than single stage. I've looked at a lot of these sites, and read a lot of these claims, but I've yet to see the first legitimate explanation of WHY they're more efficient. For that matter, I've yet to see ANY attempt to back up the claim of higher efficiency. That leads me to believe its most likely marketing hype. The fact that the operative word is "efficiency", one of the world's most overused marketing buzz-words, tends to confirm that suspicion in my mind.

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Old 12-26-2009, 05:01 AM
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Originally Posted by TubeTek
Not true at all. Nothing I said would constrain both compressors to have the same displacement. In fact, the typical single stage compressor will most always have greater displacement than a 2 stage designed for the same horsepower.



Real world numbers don't show this statement to be true. Comparing IR's current 10hp single and 2 stage offerings (to get into compressors larger than any homeowner type units and the BS performance specs that often come with them) shows the single stage produces 36cfm @ 100psi, and 33.8cfm@125 psi. The 2 stage version produces 34.2cfm when ordered in the 125psi configuration. All measurements based on free air delivery. If both units were operating at 105/125 cut in and cut out, the difference in air delivery would be difficult if not impossible to measure by commonly available methods.



What, specifically, make the 2 stage pump more efficient?



Not sure what sort of subversive intentions you might think I have, but I'm all ears and waiting for a logical explanation of this efficiency advantage, based on solid engineering principles. Since I got my degree in Mechanical Engineering from NC State a bit more than 36 years ago, I'm reasonably qualified to recognize the difference in an explanation based on engineering facts and one based on **** written by marketing type idiots that's typical of about 99% of the technical "facts" published today in reference to a wide range of equipment.



When built to equal quality standards, there should be very minimal difference in the cost of manufacture of a single stage or 2 stage pump of a given hp rating. There's few additional parts in the 2 stage, and the cost of manufacture of those parts would be partially offset by the fact that the displacement of the 2 stage will be consistently less than that of the single stage. Less total displacement = smaller components = reduced cost of manufacture.

In a 2 stage pump, we're not talking about some device that needs powder metal 4340 rods or hypereutectic pistons to survive, but rather one that operates at max pressures not much greater than cylinder pressures in a cranking but not running gas engine. When garden variety materials will get the job done, the smaller of 2 similar devices will almost always be cheaper to produce.



I stated clearly that I was excluding any application that actually needs air pressures in the upper range of pressures achievable only by a 2 stage pump. And so far, what you're talking about is "fitness for purpose" and not efficiency.



You're still discussing fitness for purpose, and not efficiency. You've selected the ability to produce high pressure as a criteria for acceptable performance when, in fact, that high pressure is seldom if ever needed in any normal shop application.



And you seem to be dreaming up things I never said. Still waiting for that expalnation of increased efficiency.



Not true by any stretch of the imagination. Spreading out the load, as you call it, enables the pump to reach a higher pressure. It does not make the pumping operation more efficient. Simple example.... I can't lift a 300# load 6 ft in the air by lifting it straight up. But I can roll it up an inclined ramp until its raised 6 ft with no problem. Does the ramp make the operation more efficient? No, it only provides a means of mechanical advantage. Technically, the process becomes less efficient when the ramp is used because rolling the load requires the effort necessary to overcome the rolling friction as well as the effort required to raise the load. The longer and more gentle the ramp angle, the more inefficient the operation becomes due to friction losses, even though the effort input within a particular expanse of time might be less. Similarly, the more spread out the load to enable compressing air to higher pressures, the less efficient the overall operation becomes due to increased frictional losses. Actual numbers from manufacturers on single and 2 stage compressors bears this out so long as both are operating within the acceptable pressure range of single stage compressors.



Still waiting for that explanation of enhanced efficiency. Lacking that, there are plenty of applications that use higher pressure air available only from multi-stage compressors. But, when you can look up the delivery specs on any legitimately rated and comparable single stage and 2 stage compressor, and see that the single stage will typically produce slightly more free air in the 100 psi range, why would you want to spend the additional money on the 2 stage if you don't need tank pressures higher than 125-130 psi?



Been there already. Didn't particularly care for it, but I ground thru to the finish. Maybe that's why I know the definition of efficiency while you obviously don't.

FWIW, a person can go to any number of sites, manufacturer and otherwise, and find claims that 2 stage compressors are more efficent than single stage. I've looked at a lot of these sites, and read a lot of these claims, but I've yet to see the first legitimate explanation of WHY they're more efficient. For that matter, I've yet to see ANY attempt to back up the claim of higher efficiency. That leads me to believe its most likely marketing hype. The fact that the operative word is "efficiency", one of the world's most overused marketing buzz-words, tends to confirm that suspicion in my mind.
Tubetek, I think you are missing the true point.


His mind is set with a misconception that will live on for eternity.

Last edited by 302 Z28; 12-26-2009 at 03:43 PM. Reason: Violation of guidelines. Please see: general board guidelines.
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Old 12-26-2009, 09:23 AM
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Tube, there's no point in us discussing this because the first part of your reply speaks volumes,

" a person can go to any number of sites, manufacturer and otherwise, and find claims that 2 stage compressors are more efficent than single stage."

They build the things but they don't know what they are talking about? OK.

And going back to school?

"Been there already. Didn't particularly care for it, but I ground thru to the finish."

That statement says volumes about your attitude!

It was boring to you I guess, sounds like you learned a lot,


"The reason is real simple. In a 2 cyl compressor, for example, you have 2 cylinders pumping air to the tank with a single stage, and one cylinder pumping to the tank in a 2 stage, while the 2nd cylinder is just pumping to the cylinder that's actually supplying the tank.

"Higher discharge temp = more wasted work = less efficiency."


By your own description of the two stage pump you think it is less efficient because it wastes energy as heat and is also wasteful by pumping air from one cylinder into another before pumping it into the tank. The single stage however is MORE efficient because it pumps directly into the tank and bypasses that wasteful step. MY, my now why didn't I and all the engineers who designed these things think of that?


You keep asking me to explain why a two stage is more efficient but you already dispute the very reason it is and think that step is just wasted energy so what's the point?


Again there is no point in arguing about this because you will disagree with anything I say and you are convinced your flawed logic is right in spite of what the manufacturers are telling you and in spite of the accepted engineering data. It is easy to twist and downplay what was said no matter how much sense it might make like when I said,

"First the single stage pump is a lot simpler and cheaper to build with a heck of a lot fewer parts and as you did correctly say they are quite sufficient for most small shops."

You replied


When built to equal quality standards, there should be very minimal difference in the cost of manufacture of a single stage or 2 stage pump of a given hp rating. There's few additional parts in the 2 stage, and the cost of manufacture of those parts would be partially offset by the fact that the displacement of the 2 stage will be consistently less than that of the single stage. Less total displacement = smaller components = reduced cost of manufacture.

In a 2 stage pump, we're not talking about some device that needs powder metal 4340 rods or hypereutectic pistons to survive, but rather one that operates at max pressures not much greater than cylinder pressures in a cranking but not running gas engine. When garden variety materials will get the job done, the smaller of 2 similar devices will almost always be cheaper to produce.



How can anyone look at the differences in a simple single stage pump and a two stage with it's higher parts count and think they are built at the same cost? I never said they had to be made of exotic materials or even different material, I simply said they are more complex and require a greater number of parts and thus cost more to build.


I think most everyone here knows better so what's the point? Again by your logic two stage pumps are not as efficient as a single stage and two stage pumps just waste energy and cost more while producing less air. So, by your thinking the ONLY reason for the existence of two stage compressors is to produce higher pressure, so I guess that makes the two stage compressors with a low shut-off pressure a total waste then.


A quick check for some manufactures' specs may be of more interest to some people than just arguing back and forth about mechanics, Eaton compressor has comparable two and single stage outfits, their 5 HP single stage compressor is rated at 14 CFM@100 PSI (it is called an 18 CFM 5 HP in the model name but they clearly point out that is pump displacement and they clearly state it is rated at the 14 CFM@100 PSI), The nearest model two stage with the same 5 HP motor is rated at 17 CFM at 175 PSI. What you are saying conflicts with just about everything that is normally accepted about compressors not just my opinion and disputes even the manufacturers, a couple of examples here,

One of many who according to you are ALL just plain wrong-

http://www.grainger.com/production/i...compressor.htm

and maybe this engineering site has it all wrong too,

http://www.hydraulicspneumatics.com/...luidPowerAcces

So I guess to sum it up everyone here who bought two stage compressors just wasted their money and would have gotten better performance from a single stage? It costs no more to build a two stage pump despite the fact is has far more parts and is much more complex? Because they produce LESS cfm a two stage compressor's sole purpose is to produce higher peak pressure despite some of them not doing so? A two stage pump simply wastes energy with that useless extra step, wonder why the engineers didn't catch that? Like I said before you write well but your logic is seriously flawed!

Last edited by oldred; 12-27-2009 at 06:18 PM.
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