View Full Version : Compressor/plasma calculations
12-26-2011, 09:15 PM
Does anyone have a formula to calculate how long my plasma cutter will cut before the compressor fires up?
The plasma cutter requires 4.5 scfm @ 80psi.
The 2 compressors I'm looking at are:
60 gallon tank single stage that delivers 11.3 scfm @ 90 psi (150 psi max)
80 gallon tank double stage that delivers 14.1 scfm @ 100 psi (175 psi max)
I just need to make the comparison so I don't under or over buy. I would like to know how to do the calculation myself so I better understand what's going on with the air supply.
"tanks" for any and all help.
12-27-2011, 09:12 AM
It is difficult to calculate exactly how long the compressor will run because (depending on the plasma cutter make and model) there are different preflow and post flow of air with the plasma units. Also....many plasma systems have different consumable parts....and the nozzle orifice size determines the air flow rate.
I know that the rating on Hypertherm units is the maximum possible flow with thye largest nozzle orifice that is made for the system.....so if you use a FineCut nozzle in a Powermax85.....it will use far less air than if you were using the 85 amp nozzle.
Good rule of thumb:
Size the compressor flow rating at 90 psi to double the plasma requirement. I would say that you need at least a compressor with a true rating of 9 cfm @ 90 psi. The larger the tank.....the longer rest between cycles.
Larger compressors last longer....and they annoy you (noise) much less. Further...there will be less moisture buildup if the compressor runs less. Either of your choices will work.....however don't forget to consider your future needs....and other air tools you may want to add to your arsenal!
Jim Colt Hypertherm
12-27-2011, 07:49 PM
Thanks for the info. You sound like you really know your stuff. I appreciate your experience in this matter.
I'm an old cad guy and I am pretty good at picturing things in my head. Here is an example of what I'm after:
Because of experience, I can picture in my head what a 110v welder can do.....and I can also picture what a 220v welder can do. I bought the Lincoln 140C (110V) because I had no need for all extra power of the 220v machine.
I bought the Powermax 30 because I'll never cut metal more than .125" thick. This too I can picture in my head and I know I purchased the correct machine.
The compressor......I have no Idea what cfm or psi can do (its the compressed air in the tank thats messing me up). I've never worked with "fluid" or "pressure" systems. When you squeeze all that air in a tank then release it at a given pressure, I can't "picture it" and I don't know how to compare the two compressors with relation to "work".
I know its not an exact science with the information that I provided.......but what I'm after is trying to figure out (with all conditions being the same) what will be the difference before the each of the compressors kicks on with my new Hypertherm PM 30 when I connect it up with a CNC table (that will be the next purchase). Like I said.....I don't want to under size the compressor.....but I don't want to get overly crazy either. At this point I have no feel for how much work 150psi can do when its bottled up in a 60 or 80 gallon tank. I do believe that the 60 gallon compressor above will work great.....I just want to get that warm fuzzy feeling before I spend the money.
Thanks for any help you (or anyone else) can offer.
12-27-2011, 08:32 PM
Unfortunately, I don't have any type of mathematical equation for you, however, I will offer the following:
There are a few pieces of equipment where "overbuying" should never be a consideration, a compressor is one of them. Get as big a compressor as you can afford and have the ability to fit/power. Always go for a two stage compressor vs a single stage if that's an option. Remember, a good name brand compressor should last a lifetime. While the lower CFM may be sufficient right now, it would be a shame to have to upgrade 10 years from now due to unforseen added equipment. Don't cheap out over a few hundred bucks.
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