single vs. 2 stage compressor

[z28toz06]

Can anyone tell me the difference?
Which is better? Which is quieter? This is big as it will be outside
Would like to be able to run an impact and a ratchet at the same time and also want to use a sander which uses 16-18 cfm.

Any info appreciated.

 

[kartracer55]

A single stage pump compresses the air then it goes into the tank. A 2 stage pump compresses air in one cylinder, and it is then cooled and further compressed into another cylinder before entering the tank. 2 stage units get to a much higher PSI than does a single stage, and some argue that 2 stages are more efficient, however I have yet to have my single stage unit struggle to keep up or not shut off for long runs at a time. It all depends on the model of each that you get.

Jim

 

[chevy302dz]

you're going to leave a compressor outside? Anything that you are going to wheel around is not going to put out the CFM you need

 

[bmwpower]

you're going to leave a compressor outside? Anything that you are going to wheel around is not going to put out the CFM you need

Could be a perminent install outside.

 

[bmwpower]

A single stage pump compresses the air then it goes into the tank. A 2 stage pump compresses air in one cylinder, and it is then cooled and further compressed into another cylinder before entering the tank. 2 stage units get to a much higher PSI than does a single stage, and some argue that 2 stages are more efficient, however I have yet to have my single stage unit struggle to keep up or not shut off for long runs at a time. It all depends on the model of each that you get.

Jim

Higher PSI not CFM, right? So the only advantage is, ultimately, a higher PSI?

 

[kartracer55]

The CFM depends on the pump speed, but definetly higher psi... My 5hp eaton is a single stage and makes 20cfm, they have a two stage that makes like 17 or 18

Jim

 

[CraigFL]

Kartracer was the closest... Using a two stage compressor will increase the efficiency of the overall unit, especially if you are compressing to a higher pressure. It's like an intercooler on a turbo car, much easier to compress cool air than hot air for a given output. But... with the advent of more efficient motors, and tools operating at lower pressures(for safety reasons), it becomes less important now.

 

[mike944]

a 2-stage with the same HP, will always put out lower CFM, because some of the motor power is being used to put the air under extra pressure, so there's less power left for moving air volume. That said, when fully pressurized, an equivalent size tank will have more "stored air" with a 2-stage, because of the higher pressure, there's more air squeezed in the tank. If you're using air continuiously, the 1 stage can give you more air per HP of the motor. If you use it intermittently, the 2-stage will have more air, because there's more stored in the tank. (assuming the same size tank)

that's the scientific answer. My thoughts? i've never seen anyone ever have use for the extra-high pressure air of a 2-stage. As to noise, they're probably about the same. If you're concerned with noise, get a compressor with cast iron cylinders, and an inlet muffler. (an "aftermarket" inlet muffler can be bought, or fabricated)

If you're installing it outside, i would be slightly worried about the oil temperature. It's going to be just like your car, cold oil doesn't like to pump. Unlike your car, where you'll idle it, or drive it easy for a short while to warm it up, your compressor is going "full throttle" right from the start. Maybe you live in a warm area, then this really doesn't mean anything to you. If you live where it gets cold, you might want to consider some type of stick-on oil pan heater, if you're really A.R. like me.

-- EDIT--
Now that i re-read your messace, i see you live in connecticut, like i do. I'd definitely be worried about proper lubrication in the winter.
________
Honda VFR800

 

[bmwpower]

And, from what I've seen, the 2 stage models are usually always more expensive.

Case in point:

1 stage:
http://www.tptools.com/product.asp?...No=1&mscssid=27R2PVX1QLCC8LUTLAG9Q4QEGH6TDX5B

2 stage:
http://www.tptools.com/product.asp?...No=1&mscssid=27R2PVX1QLCC8LUTLAG9Q4QEGH6TDX5B

Is it worth the extra $300? It doesn't seem like it.

 

[z28toz06]

So why is the 2 stage so popular?
I think I was talked out of the outside venue today by a salesman. It seems that in a cold area, which I am in would not be conducive to the compressor in freezing temps.
I learned that I can pipe the intake outside and put an intake muffler on.

So my question now is still the 2 stage vs the single stage.

also what do I need for an air dryer slash cooler,

What are you guys running?
I cant rule out spraying at some point so I need to know even if I dont get it right away what will I be best served to design in. I want to do it right the first time.

I think I will go with a Quincy but I dont know whether it will be a single or a two stage. someone talk me in to one or the other!.

 

[stimpy]

go 2 stage its more efficent, builds back up quicker ,has a higher supply pressure ,and probably be the last compressor you will buy . we have a 2 stage champion thats over 50 years old and all has been repaired so far is a newer style motor ( more efficent and runs cooler) and preventive maintance on the valves , this unit runs about 100 hours aweek sometimes for several hours straight without shutting off , go for something bigger than what you need ours is a 10 hp 220v1ph 2 stage 80 gallon tank .

 

[motorheadjohn]

A 2-stage compressor has 2 cylinders, one is larger and the other is smaller. Air is drawn into the larger cylinder first. This builds volume. The air is then pushed into the second cylinder (yes, kind of like a turbo or supercharger, since this is pressurized air now). The passage from the first cylinder to the second is usually, but not always, depending on manufacturer, a line with cooling fins, aka intercooler. The second cylinder is smaller in diameter compared to the first, and this is what builds the high pressure. From the second cyl, the air enters the tank.

Do not confuse a 2-stage compressor with a twin-cylinder single-stage. There are a few compressors out there with 2 cylinders of the same size. This is a single-stage compressor, but is a 2-cylinder.

a 2-stage with the same HP, will always put out lower CFM, because some of the motor power is being used to put the air under extra pressure, so there's less power left for moving air volume. That said, when fully pressurized, an equivalent size tank will have more "stored air" with a 2-stage, because of the higher pressure, there's more air squeezed in the tank.

Not true, unless the pressure switches are set to cut off at different PSI. Tanks of equal size pressurized to the same PSI (at the same temperature) will have an equal volume of air, regardless whether the tank was filled with a single-stage or two-stage pump. Only if your cut-off switch is set to a higher PSI will it hold more, and that's dependent on the switch adjustment, not necessarily the pump type. Single stage units might be preset to lower PSI, depending on the brand and model you buy.

 

[Satatic]

So why is the 2 stage so popular?
I think I was talked out of the outside venue today by a salesman. It seems that in a cold area, which I am in would not be conducive to the compressor in freezing temps.
I learned that I can pipe the intake outside and put an intake muffler on.

So my question now is still the 2 stage vs the single stage.

also what do I need for an air dryer slash cooler,

What are you guys running?
I cant rule out spraying at some point so I need to know even if I dont get it right away what will I be best served to design in. I want to do it right the first time.

I think I will go with a Quincy but I dont know whether it will be a single or a two stage. someone talk me in to one or the other!.

I just have two cheapo filters in series on mine and it seems to take care of the moisture.

I paint with it to. Never had a problem.

 

[Charles (in GA)]

The basic thing everyone seems to be missing is that you are not using the higher pressure, just storing it in the tank. You are regulating the pressure down to say 100 psi, no matter which compressor you are using. With the two stage, you are able to run a higher tank pressure, thus packing more air molecules in the same space. result is more usable free CFMs available to you from the tank. Most two stage units kick on about 145 psi and shut off at 175 psi, but you are regulating to 100 psi for your shop uses and sometimes lower, rarely higher (and dangerously so, as I do not know of any air tools rated or designed to use pressures higher than aprox 100 psi)

For a fixed installation, go for a two stage, the bigger the better. You cannot have two much air flow, but if you buy too small a compressor, you will regret it every time you use it.

You want the compressor to cycle on less often, and run longer each cycle. This allows the motor to operate efficently. If you frequently cycle the unit, it will build up more heat, and not last as long, burning up the start condensor, cut out contacts and switch, etc and of course, wear and tear on the pressure switch too. Everything takes a beating when that thing goes from zero to full speed in a split second, the fewer times it has to do that, the better you and it are.

Easiest way to reduce the frequency of cycles is a big tank and two stage to get higher tank pressure.

By the way, Sears has the Campbell-Hausfeld 7.5 horse, two stage, 80 gal tank model, about 24 cfm, in the catalog for about $1409, which is much cheaper than the same compressor from Home Depot ($1699). Not sure about shipping with the Sears price however (free to the store?, dunno).

Charles

 

[radmotorworks]

This topic is long standing, timeless and far reaching...

Have to say, I thought about it for a while after finding an old 2 stage brunner and considering replacing my newer single stage 3-cylinder ranger. From what I can tell (i.e, my pet theory...)--CFM is first determined by the displacement of the cylinder that is pulling in the air. As the pump rotates one cycle, the atmospheric air that gets pulled in is how much the system has to work with. Then you have to consider how many RPMs as pumps will have different flywheel sizes and motor RPMs. More actual pump cycles, more air volume intake, and more potential for compression in a given time period (this is not to say 3250 rpm motor is better than 1750 rpm one).

What happens in a single stage during the compression cycle is simply, the atmospheric air gets jammed at tank PSI all in one shot. In a two stage, you get a compression stroke which feeds into the intake of a smaller second cylinder which outputs into tank PSI. The major difference here is that the first stage cylinder outputs to an intercooler before going into the second cylinder which makes a huge difference in efficiency. Compressed air heats so, boys and girls, the air molecules expand when hot and contract when cold. More PSI means more heat.

So, what's the bottom line? Many singles like my 3 cylinder have larger atmospheric intake so they will deliver potentially higher CFM but they do it less efficiently because heated compressed air will give you less actual tank molecules which reduces PSI when it cools + more "air resistence" which will increase the load on the motor (a portable gas compressor like my emglo gets away with this problem by having a larger 5.5hp engine relative to the pump size). Two stage may give you less intake volume but the PSI range can go higher with less heat strain on pump and load on motor. The catch is that they are bulkier with an extra cylinder and tend to be more expensive.

Accordingly, if you need max CFM for less frequent blasts or have a portable application, consider a multi-cylinder single stage. If you need more constant duty and longevity and are less concerned about bulk, a 2 stage may work better--motor will need less rewinds, pump will run cooler on oil with less heat wear etc. A 3 cylinder 2-stage might give you more air intake with the benefits of intercooling. In any event, take size is the other variable, if you are getting more PSI with 2-stage it means more air molecules per tank size since you will regulate air to tool spec anyway. If you need more air at lower PSI, you simply (maybe not so simple) get a bigger tank.

Ultimately, it depends on overall intake displacement/motor RPM and if that gives you enough real CFM for your application at a required PSI. If you can get that with a 2 stage and are less concerned about expense or bulk, that might be the way to go--otherwise consider a single stage for less expense and more portability.

 

[Viper9087]

Sorry to revive an old thread but 5 years and no right answers?

Charles from GA was probably the closest.

The difference is the tank pressure.
NOT because it stores more air but because you need a higher operating pressure.

Reason 1: lets say your purpose is to blow a train horn... you need 175 psi a single stage will never reach that.

Reason 2: If you have any tools that you run over 80-90 PSI go with a 2 stage.

The difference has nothing to do with stored capacity or CFM or noise.

Keep in mind this is depending on the compressor specs:



****A single stage compressor has a lower Max PSI (lets say 135 for this example like my craftsman). I run my tools between 90 and 100 psi.

My craftsman single stage shuts off at 135psi and kicks on at 80 psi.

This means when using my impact gun... from the time the compressor kicks on till the time it reaches 90 PSI, My impact gun is useless because it is only getting 80 PSI and therefore cannot pull or tighten nuts properly or with the correct power. So I have to wait till the tank reaches 90 PSI before I continue to work.

Just to throw it in there CFM means when I start to work again at 90 PSI if my gun consumes more CFM than my tank makes, This means my pressure will drop below 90 WHILE using my gun, WHILE the tank is filling. the air cannot keep up. (have to stop and wait again).



**** A 2-Stage compressor has a higher max pressure (lets say 175 like my IR)

This means my compressor shuts off at 175 PSI and kicks on at 125 PSI

Therefore my pressure NEVER drops below 125 PSI and I can continually use my impact gun at 90 PSI without stopping.

If the CFM is higher than the tools used this means 0 downtime.



Comparable Single stage compressors DO have a higher CFM than a 2-stage but not usually by more than 5 CFM

This higher the price of the compressor.... the higher the CFM.

And you can Find 2-stage compressors with a higher CFM than a single stage. Again it's all about the price here.

Happy Compressing!

 

[volaredon]

single stage more CFM than a 2 stage? NO WAY!!!
Look at comparable displacement pumps at same RPMs/ you gotta compare apples to apples. My Emglo W series is 4 cylinders, 2 stage. (3 pump to 1st stage, 4th cyl is the 2nd stage) 2-1/2" bore and a long, 3-1/4" stroke. not all 2 stage ones have a smaller diameter 2nd stage cylinder,
I also have an Emglo KU pump, still 2-1/2" like the W pump but only 2 cylinders and 2-1/2" stroke.
Looking at (cant remember which, either a GT or a J series, have to look again to verify) both GT and J are 4 cylinders like mine, but single stage. and same bore and stroke.
so that would be a fair comparison. at the same RPM the 2 stage variant is higher CFM AND higher pressure both.
When comparing different brands, one with a 4 cyl and one with a 2 or 3 cyl., is apples and oranges.
You also gotta consider pump RPM of the particular units that you are considering.
Often they use the same pump but a different HP of motor, the smaller HP motor will have different pulley sizes and turn the pump slower.
My same W series pump on a gas application, Emglo/jenny offers this same pump with a 3 hp electric or a 5hp electric, or an 11hp gas or a honkin' 18hp gas engine.
Same pump in all instances but run at different RPMs in each case, and they publish different CFM output ratings for each.
using these particular units as my example (only since that is what I have, and so I am familiar with)

Point being, that depending on WHICH single stage and WHICH 2 stage pump that you are looking at, what RPM they are being turned at, (HP is only important because of what it takes to turn a given pump at a given RPM) you guys are ALL right in certain instances.
What is cubic inch displacement of the various pumps you are looking at? What RPMs?
just because they both have the same HP motor running them does not make for fair comparison alone.