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pgmrdan
11-08-2009, 07:25 PM
Yesterday I went to Northern Tool and was surprised that they have Quincy air compressors. Someone here mentioned Quincy as a good brand but I had never seen one. They were just about side by side with the Ingersoll Rand compressors.

The compressors I'm comparing:

Both have 60 gallon tanks.

The Quincy uses a 5hp Baldor motor while the IR uses a 5hp Emerson.

The Quincy uses a 4 cylinder 2 stage pump while the IR uses a 1 cylinder (IIRC) single stage pump.

The Quincy pump has a 5 year warranty while the IR pump has a 3 year warranty.

I'm not sure about the warranty on the motors.

The Quincy has a valve to empty the water that's sticking out from under the tank while there's something sticking down from the bottom of the IR tank but I couldn't figure out how to open it. It wasn't the usual petcock I've seen.

The Quincy weighs 475 pounds and the IR 315 pounds.

The Quincy is about $1300 while the IR is about $880.

I know the Quincy has to be a great machine but the IR is no slouch either from what I've seen in the past but the IR motor is assembled in Mexico and I have no clue about the IR pump (it looked pretty roughly finished on the outside). The Quincy appears to be an all US made machine and is nicely finished all over.

The $420 difference is quite a lot of cash and either one will probably outlast me.

What do you think? Which one would you go for?

Thanks,Dan

rbjscott
11-08-2009, 07:38 PM
Quincy, two stage. Also what is volume and pressure of each?

airsmith282
11-08-2009, 08:03 PM
which one has the better CFM rating????

BadDog
11-08-2009, 08:06 PM
For most of us, 2 stage is just wasted energy, and unwanted heat (well, maybe not in the Winter) as well as additional condensation problems. If you don't have an air lift or something that actually requires 2 stage pressures, I personally would vastly prefer a single phase. In fact, I would upgrade to a larger vertical tank rather than 2 stage. Oh, and the extra cash can go to your next purchase... :D

psomero
11-08-2009, 08:57 PM
are they cast iron or aluminum pumps?

baldor motors pretty much can't be beat, but are pricey.

a longer warranty is always better, but like others pointed out, the CFM rating of the pump is probably the most important parameter of the compressor.

MickeyD
11-08-2009, 09:21 PM
According to the Ingersoll tech that I spoke with (mine keeps crapping out) the newer Ingersoll pumps are made in India. They may make a good curry, but I am not impressed with the compressors. I would get a Quincy if it was me.

MichaelP
11-08-2009, 10:03 PM
Here is is: http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200350475_200350475

Black_Moons
11-08-2009, 10:03 PM
Id get someone to plug them in and listen to how loud they are.
I got a cheapo 5hp compressor and its soooo noisy you can't YELL in the same room as it and be heard. and thats after I made it quiter by removing the belt guard.

Another one iv heard is about talking volume.

mechanicalmagic
11-08-2009, 10:04 PM
Dan,
It depends on the CFM you need (or want). I went to Northern's site, and they show both compressors. Both are cast iron cylinders. The Quincy has a better warranty (5 vs 2). BOTH require the optional maintenance kit for that warranty.
The IR is rated at ~18 cfm @ 90 psi, the Quincy ~15 cfm @ 175 psi so the Quincy is about 60% more air, and about 60% more money. It's hard to judge the actual current draw, they both spec 5 hp.

So assuming you need only ~18 cfm @ 90 psi, it's on the side of the IR.
If you want ~28 cfm @ 90 psi, Quincy is the winner.
If you are an industrial user running the compressor hard three shifts a day, the warranty on the Quincy is hands down winner.

DJ

hardtail
11-08-2009, 11:03 PM
Go for the Quincy, this is another case of traditional excellent brand USA made outsourcing their light end stuff and trying to get by on name brand power.........you get what you pay for........if you don't need a 2 stage unit try and find Quincy's comparable model, if not buck up and pay as this well last you and possibly offspring a lifetime.........we have tons of industrial equipment at work and have a 2 stage 2 pump quincy setup in a small process lab, this thing gets basic maintenance and is still running on it's original Pirelli V belts 14 yrs later.......unheard of with it's cycle rate, we use gates belts on everything and the occasional better piece comes factory supplied with Goodyear.......the sheaves are excellent, apparently Quincy knows a winner............

lazlo
11-08-2009, 11:34 PM
The Quincy uses a 5hp Baldor motor while the IR uses a 5hp Emerson.

The Quincy uses a 4 cylinder 2 stage pump while the IR uses a 1 cylinder (IIRC) single stage pump.

I think you answered your own question: the Quincy has an American 2 stage compressor and an American motor.

MickeyD and I both have the 3HP Ingersoll-Rand single-stage: the SS3L3, and it's a Chinese motor and an Indian compressor head.
The one you're looking at is the SS5-L5. These are Ingersoll-Rand's consumer-line compressors.

Mine's been fine, Mike's has died 3 times in 3 years.

Personally, I'd get get the Quincy.

By the way, here's a good page showing Ingersoll-Rand's full product line. The professional series version of the SS5-L5 is the T-30, quite a bit more money ($1200 at Northern Tool):

http://www.autobodytoolmart.com/ingersoll-rand-shop-compressors-c-511.aspx

radkins
11-08-2009, 11:47 PM
Dan,

The IR is rated at ~18 cfm @ 90 psi, the Quincy ~15 cfm @ 175 psi so the Quincy is about 60% more air, and about 60% more money. It's hard to judge the actual current draw, they both spec 5 hp.DJ



Compressor companies are well known for stretching the truth about their performance numbers almost to the breaking point and sometimes beyond. That particular IR is a classic example and has been the subject of discussion on several different sites. A lot of those outfits exaggerate but mostly about the HP rating with a few exaggerating the CFM output however none are are as bad as that IR compressor, over 18 CFM@90 PSI with 5 HP and a single stage pump is absolutely ridiculous! A few years ago IR tried a little ruse they called "Tank assisted" CFM which is total B#!!s%^* but no one fell for it and that only lasted a very short time so then they just started exaggerating the figures. About 14 CFM@90 PSI would be closer to the truth but I would bet it would be less than that. Look at every reputable company out there and none of them even approach a CFM rating like that with 5 HP and a single stage pump, heck that would be spectacular performance for a good two stage outfit on only 5 HP!


BTW, they also have a terrible failure rate on that Emerson motor and a little research on the net should turn up a lot of info about that.

lazlo
11-08-2009, 11:53 PM
I would also be wary of the Made In USA claims on Northern Tools' web page -- they claim my IR SS3-L3 is Made In USA, and I can assure you, it's not. Aside from the motor and pump that Mike mentioned (China and India), there's no Made in USA marking anywhere on the machine. The tank has a stick-welded plaque that says "Certified by Manchester" -- is that a US company?

Edit: yes, Manchester is a US company that makes pressure vessels. So presuming that the "Certified by Manchester" means made by Manchester, then the tank is Made in USA.

http://www.mantank.com/index.htm

radkins
11-09-2009, 12:07 AM
For most of us, 2 stage is just wasted energy, and unwanted heat (well, maybe not in the Winter) as well as additional condensation problems. If you don't have an air lift or something that actually requires 2 stage pressures, I personally would vastly prefer a single phase. In fact, I would upgrade to a larger vertical tank rather than 2 stage. Oh, and the extra cash can go to your next purchase... :D


Actually a two stage is better in almost every respect simply because they are much more efficient, a single stage pumps wastes much more energy than a two stage. A good two stage pump will out perform a single stage with comparable HP and produce cooler air rather than hotter, a lot of the heat is dissipated in the transfer from the first to the second stage resulting in cooler air going into the tank. Because of the increased efficiency they will have a higher CFM rating for a given HP so the recharge times will be less resulting in a higher run vs recharge time. Generally two stage pumps run slower, quieter, produce more CFM per HP and tend to last longer so they are worth the extra cost. Upgrading to a larger tank does nothing to increase performance, any extra run time gained would be lost to the extra time it would take to recharge the larger tank so you gain nothing. A tank can only provide as much air as the pump puts in it and the recharge time will be proportional to the increased run time. The capacity of the tank is chosen by the manufacturer to control the on/off cycle rate and not for increased performance. If a tank is too small it will cycle too rapidly and if it is too big it will cause problems related to the extended recharge cycle but the performance will be essentially the same.

psomero
11-09-2009, 12:12 AM
"Certified by Manchester" -- is that a US company?




does that mean made somewhere foreign and then they ship it to their domestic facility and put their stamp (plaque?) of approval on it? that's what i'd assume...

Langanobob
11-09-2009, 08:57 AM
If you get the IR for $900 you're buying a POS and you can get one of those for $400.

I would get the Quincy. You'll have pride of ownership, will be able to power any realistic air tool or spray gun and your grandkids and probably great-grandkids will still be using it someday.

wierdscience
11-09-2009, 09:10 AM
Quincy,I know of at least two 30 y/o Quincy pumps that are still running strong.

pgmrdan
11-09-2009, 11:16 AM
Quincy it is! Thanks guys.

On a side note, I went to my tractor mechanic's place of business Saturday and we talked about air compressors for a while. His building, which had been a large full service gas station, was built in 1959 and had a Champion air compressor installed in 1960. He bought the building several years after that. The Champion air compressor is a big, beautiful, green monster that's been running for nearly 50 years without complaining. I wish I had a new one just like it. :)

BadDog
11-09-2009, 11:49 AM
Actually a two stage is better in almost every respect
You may well be an authority on the subject, but your statement goes against my intuition, and what I've heard over the years from others with more knowledge than I have. Not being argumentative, but in order to understand better, can you provide references?

1) Efficiency: Single stage compresses it once and to a lower pressure. Two stage compresses it twice, the second at higher pressure. Simple mechanical loss alone puts two stage in the red relative to single stage. And incremental increases in pressure per unit of time require more power on it's own. Much of it wasted as heat (in both stages).

2) Heat (in air): Again, your assertion is counterintuitive to me. It may have a cooling coil (usually very short) between stages, but that's not going to offset the total heat of the first stage, meaning hotter than ambient air into second stage, and obviously no affect on air from the second stage, which is also going to a still higher pressure. So the net heat increase in the tank has to be higher.

3) Slower/Quieter: I believe quieter is mostly due to slower. I've seen single stages running at lower rpms that are just as quiet as any two stage. Of course to get the same cfm per unit time, you need a bigger pump. There are also noise damping features on higher end units, some more than others depending on target market. While two stage are more prone to BE higher end units, that's not a feature specific to two stage.

4) Longevity: More a function of quality (and rpm) I think.

5) Larger Tank: I'll generally agree on that. The larger tank is just a reservoir that keeps the pump from running all the time. But it also lets a system more easily handle intermittent over demand. It is relatively rare to find a HSM system with CFM capability that will handle a constant load from sandblaster, plasma or other large consumers. The larger tank just lets it last a bit longer from it's base point to "I've got to let it catch up". Obviously a larger tank does mean more "catch up" time. But given a single user and realities of reposition/fit/whatever, this is often a quite satisfactory compromise opposed to higher hp units necessary to deliver CFM sufficient to keep up with the high discharge consumers used only rarely/intermittently. In my old home auto/body shop, the addition of a second 20 gallon tank (total of 80) made quite a nice improvement, hence my suggestion.

To summarize, the CFM capability of the compressor is the most important feature to consider (assuming you don't have power limitations). Assuming 2 compressors of the same CFM capacity, and that you don't need the higher pressure, why expend energy to pump it up there?

Can someone please explain what I'm missing, or where I went wrong?

radkins
11-09-2009, 07:08 PM
Without going into lengthy detail I will try to explain what I was talking about. A two stage pump is more efficient for the same reason a two speed transmission would be more efficient than a single speed gear box, while that may seem like an apples and oranges comparison it's really not. With a single gear box you can have low torque and high speed or you can high torque but low speed but you can't have both high torque and high speed at the same time. Likewise with a single stage compressor pump you can choose to have high volume and low pressure or low volume and high pressure but you can't have high volume and high pressure at the same time. Because of these limitations a compromise must be made and a single stage pump must be sized so that max desired pressure is reached at about the same point as the motor develops it's max power. At lower pressures this single stage pump would be capable of producing more CFM if it were sized to do so but then the motor capacity would be exceeded before reaching a desirable pressure so the compromise must be made. A two speed transmission would allow both high torque and high speed to be achieved for a given time/distance while a two stage pump will allow both higher volume and higher pressure to be achieved over a given time period. A two stage uses the large displacement piston(s) to pump high volume at low pressure into the smaller displacement section which then uses a smaller piston(s) to pump it into the tank at higher pressure.


Yes, simply put, there is enough heat dissipation between the stages to make a difference.


Quieter and longer service life is generally due to lower operating RPM but how many big heavy slow turning single stage pumps can be found on the market today?


Because of their higher efficiency two stage pumps are generally larger and slower turning but a larger slower turning single stage, while it would still be hampered by it's design inefficiencys, would only be slightly less efficient due to the slower speed and would also be quieter but heat dissipation may become a problem and it would also require a higher torque motor. The manufacturers, on these lower priced single stage outfits, tend to opt for the smaller, lighter and easier to cool pumps with a lighter lower torque motor.


Tank capacity has got to be the most misunderstood part about a compressor. Adding tank capacity can not do anything to increase performance beyond one recharge cycle unless it is for the rare case where a few seconds of extra run time would make a difference and then the compressor would be sitting idle anyway allowing it to catch up without anyone waiting on it, a very rare situation indeed. If a compressor with a 60 gallon tank is running out of air at an annoying rate then how long would it run on only a 20 gallon tank? Mere seconds right? That's all the difference there is between a 60 gallon tank and an 80 gallon so adding 20 gallons to a 60 gallon tank would add only as much time as it would have run if the tank were only 20 gallons, only seconds and then even that is lost to the extra time it takes to recharge the extra 20 gallons so what is gained? This is not speculation it is simple laws of physics and in spite of what some may believe a 60 gallon tank will keep up with tools as well as an 80 gallon all else being equal, for more than one cycle anyway. The smaller tank will run in slightly shorter cycles but more often while the larger tank will allow for slightly longer but fewer cycles, however the total run vs wait time remains the same regardless so the time available to run tools is the same during any given work period. It is a trade off and can be nothing else, again it is simple laws of physics.


In theory performance would be the same between the tank sizes over any given work period but in practice adding extra tank capacity can actually cost performance. While just adding a small amount such as going from 60 to 80 gallons is not going to matter much one way or the other adding a lot of capacity to a small compressor can cause problems. This is because as the compressor pump runs for extended periods it will tend to overheat and this reduces efficiency which means less performance instead of more.

gnm109
11-09-2009, 07:36 PM
Since I'm good at generalizations, I'll have to agree with those who say that a two stage compressor is more efficient and puts out more CFM than the typical single stage.

While a larger tank may not make a great difference, it does make some difference and I suspect that's the reason that you will see units in service stations and shops with tanks as large as 120 gallons with 15 and 20 hp 3 ph motors that will provide 30-40 cfm at 125 psi. A compressor like that is not working very hard and I've heard of some that are 50 and 60 years old and still going.

One thing that's important is to get a compressor with a tank that is ASME cerfitied. That means that it's certified for compressor use at the rated pressure. It's a mark of quality, IMHO.

I have an 80 gallon ASME vertical compressor with a two-stage unit that pumps up to 125 psi and will provide 21 CFM. It was made from US parts by a local specialty shop with a Canadian real 5hp (21 amp) motor. I like the fact that it runs slowly and also that it's still running after more than 12 years.

The units sold at places like Home Depot and Lowes are usually built to a price and have lesser quality parts. I would try to find one from a company that specializes in air tools and compressors.

If you ever hope to operate a bead blast cabinet efficiently without running the compressor most of the time during use, a larger unit with at least 18 CFM is in order. Most compressors will handle ordinary air tools and spray guns but the bead blast cabinets and outside pressurized sandblast units are the real test. JMO.

motorcyclemac
11-09-2009, 08:07 PM
If you ever hope to operate a bead blast cabinet efficiently without running the compressor most of the time during use, a larger unit with at least 18 CFM is in order. Most compressors will handle ordinary air tools and spray guns but the bead blast cabinets and outside pressurized sandblast units are the real test. JMO.

That is quite accurate. However, folks tend to run blast cabinets at far too high a pressure. I tend to get my abrasion from proper sharp media that is in good shape. High pressure tends to shatter the grit into dust. You will get longer life and better results from using garnet at a lower pressure. It doesn't destroy the media so fast and you won't have near the issue with media dust. I learned this the hard way. I destroyed my first bag of media by blasting at full line pressure. After regulating it down to 60-70 psi and using a good sharp media I discovered that the results are far better.

Cheers
Mac.

BadDog
11-09-2009, 09:40 PM
Without going into lengthy detail I will try to explain what I was talking about...

Thanks for the explanation. But I'm still not convinced, and my reasoning goes like this...

In an ideal world, with no parasitic loses, you need to expend a given amount of power to achieve a given amount of work per unit time (by definition). Higher pressure or larger tank, in the end it's still just storing power over time (also assumes air compression power in/out is linear over the target range). Increase the input power and you can reduce the time necessary to store the power required for a given amount of work (simple ratio).

So for a given amount of time, a 5hp motor is going to get you the same amount of work done at the end of the air hose regardless of the pumping mechanism. If the single stage needs to run longer to fill the larger reservoir for a target potential, then the two stage will need to run longer to store the same potential with higher pressure. The only time you will see a major shift is if running outside the working envelope of the pump design (rpm range, temp, atmosphere, pressure, etc).

But there are a several points to consider in the real world. I'll try to break my thoughts into something sensible...

1) Pump curve. How much power it takes to operate the pump with a given "head". Not sure how it stacks up between single/two stage (hence my questions), and this may be where the 2 stage wins the comparison. For a given output, I don't think this varies much over similar pumps (in this case, both are reciprocating piston) in the operating pressure range, so for now, I'll assume an effective tie(?).

2) Parasitic losses. In general, this boils down to waste heat. With more moving parts, seems the two stage is loosing that point, but how much it affects the total net power output I wouldn't know.

3) How linear is power in/out for compressed air over the pressures under consideration? I seem to recall it's starting to drop off a bit above 135 psi, but not sure.

4) Usage patterns. This can dramatically affect perceived performance, though it matters not one bit to maximum work that can be done in a unit of time (limited by hp of the motor). In my case, using DA, In-line, Power Packs, and so on; going from 60 to 80 gallons sure seemed to reduce my time spent having to wait on air pressure. But maybe I was fooling myself like all those folks who think their K&N filter improved their mpg. :D

5) And of course, like refrigeration or other similar system, you generally don't want it starting/stopping too often, nor do you want it to run constantly. And as you say, the biggest thing regulating this factor is the reservoir size, which must be suited to the pump/motor selection in order to maximize potential return for the target capacity.

6) Power utilization. Perhaps the two stage gets it's benefit by having two staggered phase pistons on the same motor? So it can utilize the excess power otherwise wasted (not used) on the intake cycle of one to compress on the other? But that would be a characteristic multi-cylinder in general, not specifically two-stage, so this is tossed out.

Anyway, my understanding (which obviously may not be correct) is that two-stage is necessary only to achieve higher pressures specifically required for things like the old auto-lifts, and for applications where you are fighting pressure drop over a distance. I'm also under the impression that the first stage of a two stage pump is functionally almost identical to a single stage, and that the second stage just kicks it up further. I guess I've heard that for so long, and with my reasoning seeming to support it, I would have to either see authoritative data or overwhelming anecdotal evidence in order to change my mind. <shrug>

But I'm not posting just for the discussion. As you suggest, 2 stage ARE much more common in the larger displacements. I have no desire for higher pressures, but with my plasma and blast cabinet, my "5hp" (ha!) 60 gallon just isn't cutting it any longer. I've got a real 5hp US made UL listed motor to replace the import crap. Now I just need to find a good pump. I want one that will capitalize on the 5hp motor and run as slow as possible (for longevity and noise). I have no desire for the higher pressure, but have considered a small 2 stage pump, and simply setting the pressure switch to 135 psi. I also have economical access to pumps OEM sized with 5hp motors It's either that or a single stage 3 cylinder single stage Eaton at about 700 rpm. My shop power limits are going to keep me from going much higher on input power, but this should make things a bit more tolerable.

Oh, almost forgot, but I don't think that "two stage cooling" is really a big determining factor. They don't usually have them, but you can put coolers between the pump and the tank on a single (or two). So while the cooling is a standard (and needed) feature between stages of a 2 stage, it's not really a characteristic of the pump. In any case, radiated heat is still lost power not stored in the tank...

radkins
11-09-2009, 11:49 PM
Since I'm good at generalizations, I'll have to agree with those who say that a two stage compressor is more efficient and puts out more CFM than the typical single stage.

While a larger tank may not make a great difference, it does make some difference and I suspect that's the reason that you will see units in service stations and shops with tanks as large as 120 gallons with 15 and 20 hp 3 ph motors that will provide 30-40 cfm at 125 psi.


You are right but the difference is not increased performance the difference is that the tanks are matched to the CFM capability of the pump and that is a different thing entirely than adding tank capacity to a small compressor in the mistaken belief that it will increase performance. Like you mention those 120 gallon tanks are being filled by 30 to 40 CFM pumps and the whole compressor is designed to deliver large volumes of air for extended periods. A 60 gallon tank on one of these would be way too small for the same reason that a 25 gallon tank would be too small for a 5 HP 12 to 14 CFM compressor. Actually the big 40 CFM outfit would work just fine with a 60 gallon tank if it was only used for 10 to 12 CFM duty but these things are made for much more than that so the bigger tank is there to provide a reasonable on/off cycle rate during heavy demand it is not there to provide higher performance. As long as the compressor is operated within it's intended range the tank chosen by the manufacturer should provide a good balance between run and recharge cycles. If a compressor demand exceeds it's CFM rating, as often happens, then the cycle rate becomes unbalanced with excessively frequent on/off cycles which can cause overheating and other problems. Adding tank capacity without increasing CFM just compounds the problem due to excessive recharge times and can cause overheating in an otherwise acceptable situation, the same thing would happen with that 40 CFM unit if someone tried to use it, for example, for 60 CFM service. So those big 20 HP outfits have 120 gallon tanks to provide a proper balance at the 30 or so CFM demands they are capable of, demands that a 5 HP 14 CFM unit could never sustain. The bottom line is the size of the tank is to control the cycle rate and adding tank capacity does nothing to increase it's usable time over any given work period, that's not it's purpose and in fact it would be impossible for it to do so since a tank can only deliver as much air over a given use period as the pump produces regardless of tank size, again it's just simple laws of physics.

radkins
11-10-2009, 12:38 AM
In an ideal world, with no parasitic loses, you need to expend a given amount of power to achieve a given amount of work per unit time (by definition). Higher pressure or larger tank, in the end it's still just storing power over time (also assumes air compression power in/out is linear over the target range). Increase the input power and you can reduce the time necessary to store the power required for a given amount of work (simple ratio)....

I am a bit confused by what you mean there so I can't comment on that.



So for a given amount of time, a 5hp motor is going to get you the same amount of work done at the end of the air hose regardless of the pumping mechanism. If the single stage needs to run longer to fill the larger reservoir for a target potential, then the two stage will need to run longer to store the same potential with higher pressure. The only time you will see a major shift is if running outside the working envelope of the pump design (rpm range, temp, atmosphere, pressure, etc)....


Well it would work that way IF the pumps were 100% efficient and all of the motor's energy was used to compress air but unfortunately neither pump even comes close. With the better efficiency of the two stage a motor of a given power, for instance 5 HP, will be able to produce more CFM so it would take less time to reach a desired volume and pressure. During a given work period of more than one cycle the two stage will have the advantage in that it can recharge the tank faster so the compressor will be available for use for more time during that period. Basically you can think of it like this, a two stage let's you have a bigger compressor for the same amount of HP because less of the motor's power is wasted with the two stage vs the single stage.


But there are a several points to consider in the real world. I'll try to break my thoughts into something sensible...

1) Pump curve. How much power it takes to operate the pump with a given "head". Not sure how it stacks up between single/two stage (hence my questions), and this may be where the 2 stage wins the comparison. For a given output, I don't think this varies much over similar pumps (in this case, both are reciprocating piston) in the operating pressure range, so for now, I'll assume an effective tie(?).

2) Parasitic losses. In general, this boils down to waste heat. With more moving parts, seems the two stage is loosing that point, but how much it affects the total net power output I wouldn't know.

3) How linear is power in/out for compressed air over the pressures under consideration? I seem to recall it's starting to drop off a bit above 135 psi, but not sure.

4) Usage patterns. This can dramatically affect perceived performance, though it matters not one bit to maximum work that can be done in a unit of time (limited by hp of the motor). In my case, using DA, In-line, Power Packs, and so on; going from 60 to 80 gallons sure seemed to reduce my time spent having to wait on air pressure. But maybe I was fooling myself like all those folks who think their K&N filter improved their mpg. :D

5) And of course, like refrigeration or other similar system, you generally don't want it starting/stopping too often, nor do you want it to run constantly. And as you say, the biggest thing regulating this factor is the reservoir size, which must be suited to the pump/motor selection in order to maximize potential return for the target capacity.

6) Power utilization. Perhaps the two stage gets it's benefit by having two staggered phase pistons on the same motor? So it can utilize the excess power otherwise wasted (not used) on the intake cycle of one to compress on the other? But that would be a characteristic multi-cylinder in general, not specifically two-stage, so this is tossed out.

Anyway, my understanding (which obviously may not be correct) is that two-stage is necessary only to achieve higher pressures specifically required for things like the old auto-lifts, and for applications where you are fighting pressure drop over a distance. I'm also under the impression that the first stage of a two stage pump is functionally almost identical to a single stage, and that the second stage just kicks it up further. I guess I've heard that for so long, and with my reasoning seeming to support it, I would have to either see authoritative data or overwhelming anecdotal evidence in order to change my mind. <shrug>....


You got close with no.6 but then you tossed it out, the two stage has a large piston for volume in the first stage and a smaller piston for the second or higher pressure stage. If you go back to the other post where I compared this to a gear box then that is what I was talking about. With a single speed gear box you could have lots of pulling power but no high speed OR you could gear for a higher speed but you would not have much pulling power. Same thing with these pumps, a single stage with a big piston for large volume would make a lot of CFM but as the pressure increased the motor load would also increase requiring either a huge motor or stopping at a low pressure. If the pump had a small piston then the pressure could go much higher for the same HP but the CFM would be so low it would take a long time to charge the tank. The two stage takes advantage of both a large and a small piston to achieve both higher volume and high pressure making it more efficient and converting more of the motor's energy to compressed air.


But I'm not posting just for the discussion. As you suggest, 2 stage ARE much more common in the larger displacements. I have no desire for higher pressures, but with my plasma and blast cabinet, my "5hp" (ha!) 60 gallon just isn't cutting it any longer. I've got a real 5hp US made UL listed motor to replace the import crap. Now I just need to find a good pump. I want one that will capitalize on the 5hp motor and run as slow as possible (for longevity and noise). I have no desire for the higher pressure, but have considered a small 2 stage pump, and simply setting the pressure switch to 135 psi....

Some two stage pumps do have a lower shut off than the common 175 PSI and this is done to maximize CFM. Simply adjusting the switch down to 135 PSI would not do the trick however and would only have the effect of a smaller tank, lower pressure in the tank means less cubic feet stored in it. If 135 PSI is what you want (good idea IMO) then set the switch for that cutout level then increase pump RPM by using different pulleys (or just use a larger pump than you would if you were to going to 175 PSI) so that the motor is nearing it's rated AMP draw just as the compressor reaches the 135 PSI. If you have a two stage pump and the motor reaches it's AMP rating (use a clamp meter to determine this) just as the pump is reaching the 135 PSI then you will be producing the max amount of CFM.




I also have economical access to pumps OEM sized with 5hp motors It's either that or a single stage 3 cylinder single stage Eaton at about 700 rpm. My shop power limits are going to keep me from going much higher on input power, but this should make things a bit more tolerable.

Oh, almost forgot, but I don't think that "two stage cooling" is really a big determining factor. They don't usually have them, but you can put coolers between the pump and the tank on a single (or two). So while the cooling is a standard (and needed) feature between stages of a 2 stage, it's not really a characteristic of the pump. In any case, radiated heat is still lost power not stored in the tank...


Heat is going to be a byproduct of compression, no way around it, but once that heat is produced the last place you want it is in the tank! The hotter the air, the less efficiently your compressor is working.

pgmrdan
11-10-2009, 12:44 PM
I left the house early this morning and went by a well respected tool store. I wanted to look at the air compressors they carry that have American in the brand name.

The motors are made in Mexico.

The pumps are either made in Brazil or India.

I'm not positive any part of their compressors are made in the US.

They were priced like they were Quincy brand.

Sad.

BadDog
11-10-2009, 12:59 PM
Thanks for taking the time to answer.

So, sounds like you know quite a bit about compressors. You've convinced me to reconsider those two stage pumps I have access to. They are true industrial pumps, and I can get one of those and rebuild it for a lot less than an Eaton 3 cylinder, plus I know the guy would let me return it if it's not salvageable. Some are on 60-80 gallon tanks and have 5hp 3ph motors, so obviously that's a good starting point. Unfortunately, these small compressors are all on horizontal tanks, so I'll be using my 60 upright (US made) tank. I also don't want to have to run my RPC all the time to service the compressor, so I'll be using my US made 5hp UL rated 1ph motor.

So, other than matching tank size and motor power, can you give me any suggestions for what to look for? In-line vs V? I don't have an huge supply of pulleys to play with while checking load on the motor, so can you suggest an approximate desirable ratio? Or maybe delta from the OEM setup? I assume it's not a straight ratio with the pressure differential.

radkins
11-10-2009, 02:29 PM
Without knowing exactly which pump you intend to use I can only make some generalized suggestions but it may help. Piston configuration on the two stage will not be much concern but a single stage seems to benefit from a V-type layout due to better cooling of this type of arrangement. Most single stage pumps will turn between 900 and 1100 RPM so just size your pulley ratio based on the motor RPM but two stage pump speed varies quite a bit with manufacturer. Generally the largest pump that your motor can turn to it's minimum operational speed is ideal so starting with your motor's AMP rating and running speed you can look for a pump to match that. If you have a true 5 HP motor of at least 21 AMPs then look for a two stage pump that produces about 15 CFM@175 PSI, if the motor is rated as much as 28 AMPs then you can go slightly higher on the CFM (around 16 or 17 CFM@175 PSI. I know you intend to set your shutoff pressure lower but the pump specs will most likely be at 175 PSI, set up properly at the lower cut off will give you more CFM than the rating.

Actually with a 21 AMP motor turning a 17 CFM two stage pump at it's minimum operational speed and cut off set at 135 should put you right on target, just use a good clamp meter to measure AMP draw on the motor as the compressor reaches shut off pressure to verify that you are not overloading the motor and you should be right in business. :)