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1-stage vs. 2-stage (again)

J

JHines

Well Known Member
A bit off-topic, but I am looking to upgrade my compressor. Going with a 230V, single-phase, oil-lubricated unit. I've read a lot of positive recommendations for two-stage units here. Problem is, from my research, the "high-end" of the single-stage units are rated a lot better per dollar than the "low-end" two-stage units. I know that "HP" ratings are to be regarded with suspicion, but how reliable are the CFM ratings?

Example - two Ingersoll-Rand units with the same warranty:

#1, single-stage, continuous-duty motor, 60 gal. tank, 18.X CFM@90PSI, 15.X CFM@135PSI, $900.

#2, two-stage, continuous-duty motor, 60 gal. tank, 14.X CFM@90PSI, 14.X PSI@175PSI, $1200.

I don't have any need for air over 135 PSI. So I guess my question is, is there some compelling attribute about the two-stage unit that makes it worth 33% more money when the performance is worse?
 
Biggest advantages of 2-stage over 1-stage is that they produce 1/2 the noise and last twice as long.
 
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Mel said:
Biggest advantages of 2-stage over 1-stage is that they produce 1/2 the noise and last twice as long.
Click to expand...

Right, another thing too : typically, they will have a higher pressure rating.
 
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Less Water

The 2 stage recommended to me (eatoncompressor.com) was recommended because of the noise and life-span factors Mel mentioned, but since it had an inter-cooler and after-cooler, it would produce less water. I just ordered it, so I can't give any indication of what reality will be, but, I live on the Gulf Coast and humidity is frequently above 80% year-round, so I could easily see how issues with water would arise.

Just a thought,
Michael
 
My 2-stage has been running well in my shop for over 20 years without so much as a hiccup. I drain very little water from it and change the oil annually.
Before that, I went through single stage compressors about every 3-4 years. I use air a lot!
 
Water comparsons are bogus

There is nowhere on either style of compressor for water to escape after the moisture laden air enters the initial intake filter. Therefore, for the same final tank pressure and cfm, the liquid water production will be the same and the tank draining will be the same.

The intercooling coil on 2-stage units is to increase compression efficiency (reduce power required to produce X cfm at Y pressure).

I have a 2 cylinder single stage Coleman 6.5hp rated for 10 cfm @ 90psi (top pressure 140 psi). I purchased 4-5 years ago at Tractor Supply for less than 400 bucks. It has been a great replacement for the 50 year old 2 stage that I had previously. Even though it is in the basement, it is quiet enough that sometimes I don't bother to get up and turn it off in the middle of the night after accidentally leaving it on.
 
Doesn't a two stage run cooler, not causing air to get as warm, causing less moisture as air cools back off? Although moisture not a big reason for purchasing.
Also, by having higher pressure, obviously your compressor would not kick on as much and handle running tools longer with the same size tank.

J Hines,

I would be curious what kind of amps the compressors are pulling on the two you are comparing. Probably not a big deal in $$ of electrical costs, unless you use a lot of air. The two stage should be lower but maybe not.
 
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Path independant

Two points:
If you have a chance to touch the intercooler on a two stage, do it quick because the fins are VERY hot and will burn severely. :eek:

Second, from a thermodynamics standpoint, the "path" from ambient air to the compressed state inside the tank is irrelevant except in regards to how much power is used. One only needs to consider the pressure, temperature and water content of the beginning state and the end state. The water content will be the same for both states because there is nowhere for water to escape during compression. Obviously if you start with enough, some will precipitate out in the tank.

If the two different types of compressor are set to provide the same CFM and final pressure, they will intake the same amount of air and water. The amount of water that the air can hold while in the tank is dependant on the final temperature and pressure, not the path that got you there. There will be a difference in the amount of power used by each compressor. All being equal, the 2-stage with intercooling should use less. However, at the size we are using and at hobbyists usage rates, the difference is indistiguishable.

My view is buy based on the best oiled compressor "deal" you can find, and don't rule out either style.
 
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Pallet said:
Doesn't a two stage run cooler, not causing air to get as warm, causing less moisture as air cools back off? Although moisture not a big reason for purchasing.
Also, by having higher pressure, obviously your compressor would not kick on as much and handle running tools longer with the same size tank.

J Hines,

I would be curious what kind of amps the compressors are pulling on the two you are comparing. Probably not a big deal in $$ of electrical costs, unless you use a lot of air. The two stage should be lower but maybe not.
Click to expand...

From the specs looks like 21 Amps for the single-stage and 15 for the two-stage.
 
Jonathan,
Thanks. I see the two stage is lower as I suspected, but the single is also putting out a little more air.
All depends how much you will use it.
I own a single stage oiled portable for moving to different places and a larger two stage oiled for in the shop. Definately reccomend oiled since they are normally quieter.
 
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