2 stage or single stage ?

any thoughts...

Fred

Charles

You also have the advantage when the tank pressure is at 175 of not risking dipping below 100 psi when consuming large amounts of air. With a two stage 175 psi compressor the pump will cycle on at about 145 or 150 and pump back up to 175. Even running a blast cabinet or die grinder will probably not cause the air pressure to continue to drop enough to be noticed. With a single stage, 125 psi pump, the pump doesn't come on till 100 or 105, right where you are regulated to. When you are consuming high CFM's and the pump kicks in at 100 psi, then you will experience a dip in pressure before the pump catches up and brings it back up above 100 (if it does at all).

If you are going to install a stationary comoressor and have 220V available, you certainly should consider the two stage, you will be better off in the long run.

One thing you will discover is more uses for the air. Without a compressor, you are thinking "blow nozzle" and "impact wrench". After you get the compressor, you will be thinking, "blast cabinet, die grinder, air drill, sander, etc" Suddenly you start wishing for more CFM's of output capacity, that you didn't buy.

I had a older Sears "4 hp" 20 gal tank, aluminum/steel sleeved oil lubed pump, 220v compressor. It did OK but could not keep up with a die grinder, even the good Dotco one (which consumes less air than the cheap ones) I would have to stop and wait on the compressor, it would get very hot and the electric consumption was noticable. I bought a 80 gal two stage, 7.5 hp, 24 CFM compressor. I never wait on it and it doesn't run alot. The electric consumption is no more and possibly a little less.

Charles

Thats exactly what happened! I had a direct drive compressor with 25 gal tank, noisy as all hell, good for blow gun and impact. Couldnt stand the noise, sold it and bought a 3 cyl, single stage, cast iron, belt driven unit. It is doing the job very well now... but I started to use the sand blaster and it keeps up fine, but runs alot, anyhow I dont sand blast often so thats ok.

I did some research before buying the compressor, but never really understood the advantage of having a 2 stage. So I went with best price and good CFM's, for my home use I dont regret it, I think it will last a very long time.

I attached the link of my unit, paid it $800 CDN thats ~$670 USD brand new(I paid cost price).

http://www.eaglecompressor.com/_egl08whl13dl04ctnt61/products/compressors/eagle/single_stage_150/C5160V1.html

You need to add a _link title_ as well to give us something to click on. ype something - anything - into that field as well.

--->Paul

• air link

A two stage is better for the following reasons:

1. Can operate easily to a higher pressure - e.g. 175 psig as compared with 125 or 135 psig. That means more cubic feet of air can be stored in the same sized tank and gives a longer time period between compressor starts for a similar air consumption.

2. Cooler discharge temperatures. A two-stage discharging at 175 psig operates at a lower compression ratio per stage than a single stage operating at 125. For example the first stage discharge would be about 40 psig. The air would then typically be passed through an intercooler device (finned tubing) before being introduced into the second stage where it would be compressed and discharged at 175 psig. The compression ratios per stage would be about the same at 3.6:1. By comparison, the single stage, when discharging at 125 psig, has a compression ratio of about 9.5:1. The higher compression ratio with no opportunity for any interstage cooling results in higher discharge temperatures. This, in turn causes everything to run hotter with less moisture dropout in the storage tank. This is particularly noticeable when a single stage is of marginal capacity for the usage and runs for lengthy periods with little down time for cooling off. Most two-stage units are designed and rated for continuous operation without overheating. I question if most single stage ones are.

3. More efficient regarding power required for the same capacity.

The first two above are the more important considerations for a home shop unit as the power difference is small in the size units generally used in such instances. If you were talking 50 HP (or more) units, the power savings of a two-stage could be a key decision factor. In general, the two-stage would be expected to cost more for a similar capacity.

Rod

that answers my question !

I was thinking more in the lines of 5 HP units (home shop use).

So if I understand correctly, the 2 stage would produce less condensation in the tank as well ?

but as you and others pointed out the pressure is also an important factor since it plays a major role in avaialble air from the tank before re-start.

or am I still confused :)