Air Supply Requirements for Plasma Cutting Systems (Plasma Cutter Air Compressors)
Plasma is a superheated ionized gas. In a plasma cutting system, you can think of this as a lightning bolt inside a tornado.
The electrical current (lightning bolt) contains a massive amount of heat energy. The gas (tornado) ionizes, controls the arc, and blows away the molten material. In order for a plasma cutting system to perform optimally, the gas supply must be clean, dry, and properly regulated. When using bottled gas, these factors are relatively simple to control. Since most modern plasma cutting systems rely on shop air for the majority of cutting processes, more variables are introduced into the equation, often causing performance and consumable life to suffer when the air supply is less than ideal.
Here we’ll discuss the three factors that contribute the most to the performance of your plasma cutting system, and how to make sure that your tornado can keep up with your lightning bolt.
Before we can discuss what a plasma cutter needs to breathe, we need to understand the design and operation of air compressors. A typical air compressor is comprised of a motor-driven compressor and a storage tank. The storage tank size will be represented in gallons or liters, with portable systems having tanks as small as 1 gallon and stationary systems having tanks 100 gallons or larger.
Flow rate capacity is a product of output pressure and storage tank size. The higher the output pressure is set, the lower the flow rate capacity will be. It is important that you are confident your compressor can keep up with the flow rate requirement of your cutting system when set at the required output pressure.
It is highly recommended that your plasma cutter air compressor be dedicated to running your plasma cutting system. If you plan to run other pneumatic devices simultaneously, you will have to add the flow rate requirements of all devices together to ensure that your compressor can keep up without exceeding its duty cycle.
Pressure is the force of the compressed air being fed to your plasma cutter. The value for gas pressure may be represented in pounds per square inch (psi), megapascal (MPa) or bar.
Air compressor system pressure is preset and is usually between 100 psi and 135 psi and output pressure is adjustable via the pressure regulator. Inlet pressures vary by system. For a small handheld plasma cutter running at 20-30 amps, you’ll need as little as 80 psi (5.5 bar). Larger, automated plasma cutting systems in the 130 to 800 amp range may require 115 psi (8 bar) or more.
Most commercial industrial air compressors for plasma cutters will be capable of generating pressures in this range. It is important to note that the inlet pressure at your plasma cutting system will be lower than the output pressure of your air compressor due to pressure drops between the two points which can be caused by leaks or restrictions such as undersized fittings or filtration units.
You may need to set your compressor’s output pressure slightly higher than the inlet pressure requirement of your plasma cutter to compensate for pressure drops. Consult your operator’s manual to determine the best pressure for your system.
Flow is the rate at which air is being fed to your plasma cutter from the air compressor.
The value for flow rate may be represented in cubic feet per minute (CFM or ft3/min), standardized cubic feet per minute (SCFM), cubic feet per hour (CFH or ft3/h), standardized cubic feet per hour (SCFH), liters per minute (l/min), or liters per hour (l/hr). The flow capacity of a compressed air system is largely determined by the size of the tank.
As a good rule of thumb, select a compressor that has a flow rate capacity of at least 1.5 times the consumption rate of the plasma cutter. You’ll also want to make sure that the hose or tubing in use is rated for the pressure the system will handle, large enough in diameter to handle the flow rate requirements, and will not corrode or cause excess moisture to develop inside the line.
Copper is preferable to steel and aluminum pipe. Lines shorter than 75’ should use 3/8” diameter hose or tubing. Lines longer than 75’ should use ½” diameter hose or tubing. If using a flexible hose, you should take care to make sure the hose is not pinched or kinked.
The orifice size of all fittings used should match the ID of the hose or tubing. Flow rate requirements also vary by system and you’ll need between 3.5 scfm (99 l/min) and 6.7 scfm (189 l/min) depending on your system’s requirements.
While inlet pressure and flow rate vary by system, filtration requirements do not. At surface level, it may seem that this makes filtration the simplest variable to account for.
In truth, filtration is the biggest gremlin in many air supply systems. It is often misunderstood and operators assume that because they have invested in the proper filtration equipment, they cannot possibly be experiencing a filtration issue.
The design and layout of a compressed air system can have a large impact on the amount of moisture that becomes trapped in the system, and where it ends up. Gravity can be your friend or enemy in this regard. Air filtration devices should be used to remove water, oil, and debris from your air supply and should be placed as close to the plasma cutting system as possible.
Under most conditions, a common coalescing filter with an automatic drain is sufficient. If cutting in a high humidity environment, a refrigerated air dryer should be considered.
Taking the time to ensure a proper supply of clean dry air to your plasma cutting system will provide you with better cut quality, less downtime, and longer-lasting consumables. If you need help selecting the proper air compressor or air system components, visit your local supplier for assistance!
If you’d like to learn more about plasma cutting, you should read our blog detailing how to properly replace your CNC plasma consumables.