:confused: Can some one explain the Pros and Cons of a 2 stage compressor over a single stage? TIA.
Conclusion, well worth the cost.
Two stage compressors don't need to work as hard to produce the same amount of air.
Originally Posted by justing70
Hi Len and everyone,
If I have a 2-stage, 25gallons, 175psi compressor, would I have the same air as a 60 gallons single stage, 135psi?. Andy
For one thing the 60 gallon tank will allow the compressor to go a lot further before it needs to start pumping. PSI isn't really that important it's the CFM that will determine if the compressor has enough output. The CFM is usually determined by several factors like horse power, compressor displacement, fly and drive wheel ratios and so on. If you know the CFM of each compressor you will know if you are limited to certain tools. It would be advisable to go with the 60 gallon model if possible, especially if you're planning on spraying an entire vehicle.
single stage vs 2 stage
2 stage compressors are better at getting rid of heat. air is compressed by the first stage piston first, then travels thru a copper pipe to the next piston. the copper pipe usually snakes its way by the flywheel which doubles as a fan and loses lots of heat there. then it is compressed by the second stage piston. because of better cooling they can safely pump to higher pressures. single stage suffer above 110 lbs while 2 stage can go to 175 or 200 lbs. it is not good to have the compressor starting and starting all the time so if you have a big compressor being able to pump to a higher pressure is better for the electric motor. that said air at 175 psi is still very hot and a serious attempt at getting it cooled down before the tool using it is necessary. usually some kind of aftercooler. dissicant air driers break down if the air is hotter than 100 degrees, and water traps can't trap water vapor , and it will be water vapor if the air is hot. for every 20 degrees the amount of water the air can hold doubles.
flatsixcrazy, It sounds to me like you're talking about that little Sears compressor that is a two stage unit with a 25 gallon tank that they ERRONEOUSLY advertise as it being comparable to a 60 gallon single stage compressor. I personally drove to sears and inspected that little compressor just to satisfy my own curiosity. That compressor is a waste of my money for anyone wanting to do autobody work or paint work. It may have a two stage pump and it may be setup to shut off at 170 psi meaning more air in the air (at higher pressure) but single most important statistic of ANY air compressor is CFM. That little sears 2 stage unit puts out somewhere near 6.5 cfm. Just about all bodyshop/paint shop tools use more than 6.5 cfm so you'll be beating a dead horse right from the get go.
Sears advertisement for that air compressor is deceptive advertising simple to con people who don't know any better into buying that unit. Like I said - that compressor is a waste of money if you plan doing any real bodywork or painting.
One other point to add about REAL two stage compressors (not that little sears 25 gallon thing) is that most two stage compressors have a much slower rpm than their singel stage counterparts. A good quality 2 stage compressor will run at between 600 - 1,000 rpm while a lot of the single stage units run up to 2,000 rpm or more. More rpm = more heat, wear out faster, produce more water etc.
I must respectfully disagree. The advantage of two stage is simply the higher pressure in the tank but single stage compressors using multiple cylinders are capable of delivering much higher CFM than two stage compressors of comparable HP and size. All two stage compressors have two cylinders at least the first gets the air to 125 PSI and the second to 175.
Campbell-Hausfeld and Emglo (no longer exists as it was bought out by DeWalt and the manufacturing moved from Johnstown, PA to Mexico) both made units bascially using a modified two stage head that was single stage that gave very high CFM. Campbell calls their unit the QuadZilla and it truly has a very impressive CFM output at 135 PSI which is more than sufficient. I-R also makes a single stage unit using this idea that puts out a lot more air than an equivelently sized two stage.
I've got a two stage 80 gallon vertical Quincy that has served me well but from the bang for the buck point a view a multiple cylinder single stage was what Emglo recommended for body shop usage to me 20 years ago and I think they were probably right.
The reason for the high output is that they bore out the second cylinder (or third and fourth cylinder) which is smaller for technical reasons in a two stage to the same size as the first stage cylinder thus increasing the CFM.
You stated - " I-R also makes a single stage unit using this idea that puts out a lot more air than an equivelently sized two stage". (end quote).
If the two compressors pumps (one single stage and one two stage) were of equivalent size then the two stage pump will pump more air as it is more efficient at pumping air. My experience is that single stage compressors are in almost all cases run at higher rpms than their equivalent 2-stage units. In that case the single stage pump will pump the same amount of air as a two stage but - at a cost. That cost would be higher running temperatures, moving parts fail quicker, more moisture production.
Phil, The single stage units that I'm describing employ the same heads that a double stage uses only instead of the initial compression cylinder (stage 1) being larger than the secondary (stage 2) cylinder of the two stage configuration both cylinders are of the same size. Because of this the two of them together have a larger displacement than the combined value of the typical first and second stage cylinders thus they have a higher CFM at 135 psig. The intercooler used between the two cylinders (or in two stage versions first and second stages) are identical thus the hotter cooler argument is invalid. It's just a simple cubic inches equation leading to the greater output for the single stage variation. Go to sears.com and look up the I-R compressors you will see what I'm talking about as they have what appear externally to be identical compressors but one is single and the other two stage and the single has a significantly higher CFM output.
Dennis, with all due respect I think you're comparing apple and bannanas. In order to make a realistic comparison I'd have to have the model numbers of both IR air compressor units. I would appreciate it if you would supply the two cmpressor model numbers (not like T-30 but actual model numbers which are applied to each individual model of air compressor ).
For a while I worked at one of the Sears parts & repair centers. Listen to this STAY AWAY FROM THAT COMPRESSOR All the oiless compressors FAIL! many that was brought in to be repaired could not be fixed.
Here Phil is an example of what I'm talking about. This is the Campbell-Hausfeld version of this situation but I-R's is the same. I-R's site doesn't list all of their various compresssor combinations so I had to use C-H for this comparision
This is the single stage
This is the double stage based on the same platform. As you can see the rated CFM of the single stage at 90 PSIG is greater than for the double stage and the cost is substantially less as well.