Next to Power, Air is the life blood of your plasma cutter. So many people think air is just air, and that all air is created equal.. That is not true for plasma. Lets make sure we are on the same page. We are talking about Air Plasma Systems here, not High Definition systems that use oxygen, Argon and other gases. Specifically, we will be talking about the Hypertherm Powermax series plasma cutters which are air plasma cutting units.
Air quality can dramatically affect several things: Cut quality, machine life, and consumable life.
In the plasma cutters section we talked about how much air you would need, which is about 7 to 8 CFM (cubic feet a minute) at 90 psi. This really is not a lot of air and most compressors can handle this. There are a few factors that you need to consider though, when selecting the compressor that is going to supply your air. Your basic 3 to 5 HP 60 gallon compressor you would find at Home Depot or Lowes can usually output 11 CFM. This will handle the demands of most plasma cutters, but you need to consider if you are going to use any other air at the same time. With this size of compressor only being about 3 CFM above the minimum and only having a 60 gallon tank, your compressor will likely be running non-stop. Which most of the cheap 60 gallon compressors are not designed for.
My recommendation is if you’re using a 4×4 table, get a 5HP 60 gallon at a minimum. If you have a 4×8 or larger, you need to be at a minimum 5HP 80 gallon tank or larger. Ideally your compressor should be able to output 1.5 to 2 times the CFM needs of your plasma cutter. Which is about 14 CFM at 90 psi.
I really like the EMAX brand compressors. They have many models, but their silent air series are really nice. They come in 5hp, 7.5HP, 10hp and 15HP and are available through Home Depot. Nice and quiet, High CFM, and a great warranty.
Here is a link to check a model on the Home Depot website:
Their 7.5HP Silent compressor has an incredible output of 31 CFM @100 psi and operates at a super Quite 60 DBA. This would be the compressor of choice for a 5×10 plasma table, or where you are cutting non stop. Plenty of air to keep up and super quiet. Here is a link:
The EMAX Brand compressors come with a lot of nice options included like the automatic tank drain and a great warranty.
For Price, quality, options, noise levels, and durability.. EMAX is my first choice.
Delivering the CFM to your compressor
Rarely do we place the compressor right next to the plasma machine, for many reasons, so we need to pipe the air to the Plasma Unit. Distance and the size of your air line will hurt you more than you know. here are some examples.
Lets go back to the cheap 4hp compressor 60 gallon tank, 11 CFM at 90 psi 150 psi max. We hook up your typical 3/8 100 ft air line which has an inside diameter close to .25 inches, You’re going to deliver 4.56 CFM to that plasma cutter. Shorten that air line to 50 feet, and you will deliver 6.45 CFM to the plasma cutter. Now change the inside diameter of your air hose to .50, and a 100 foot hose will get 25.80 CFM to the plasma unit. More than your compressor can deliver in this case.
I see this all the time, on the forums people are getting cut errors on their plasma cutter because the machine is not getting enough air. They say the pressure gauge says 120 psi, they have a compressor that can deliver 11 CFM, and they only need 7.. so what is the problem? They blame the plasma unit. With plasma cutting we need both volume and pressure. The volume must meet the requirements at the required pressure. Airline supply diameter has a huge influence on weather you can get the necessary CFM to the plasma cutter. It’s not uncommon to have longer runs than 100 feet.
So we talked about the compressor, air lines, and ensuring we get enough air to the compressor.. but now we need to address quality of the air that we deliver. To get the best results on our cuts we need to ensure that we deliver the cleanest, driest air possible. No particles, no oil, no moisture. Will your plasma cutter work if these things are present? Sure, but just not as well as it could. You can waste lots of money and time, putting in a bunch of copper tubing or desiccant dryers that you will have to change continually, or you can do the best thing for your system and install a refrigerated air dryer in your system.
Additional Air information resources – Compressed Air Tech Tips