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How to Select Air Compressor for Your Plasma Cutter

How to Select Air Compressor for Your Plasma Cutter

Plasma is a superheated ionized gas. In a plasma cutter air compressor system, you can think of this as a lightning bolt inside a tornado. 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.

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, it introduces more variables into the equation. Oftentimes, this causes 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.

About Plasma Cutter Air Compressors

A typical air compressor comprises of a motor-driven compressor and a storage tank. The storage tank size is represented in gallons or liters. Portable systems have tanks as small as 1 gallon, and stationary systems have tanks of 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. This ensures that your compressor can keep up without exceeding its duty cycle. 

1. Pressure 

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 usually between 100 psi and 135 psi. 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. 

2. Flow 

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 size of the tank largely determines the flow capacity of the compressed air system.

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 make sure not to pinch or kink the hose.

The orifice size of all fittings used should match the ID of the hose or tubing. Flow rate requirements also vary by system. You’ll need between 3.5 scfm (99 l/min) and 6.7 scfm (189 l/min) depending on your system’s requirements. 

3. Filtration 

While inlet pressure and flow rate vary by system, filtration requirements do not. At the 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 because it is often misunderstood. 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. You should use air filtration devices to remove water, oil, and debris from your air supply. Place these 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, consider a refrigerated air dryer. 

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! 

PLASMA GAS SELECTION GUIDE

Plasma Gas Shield Gas Mild Steel Stainless Steel Aluminum
Air Air Good cut quality Economical Good cut quality and speed Economical Good cut quality and speed Economical
Oxygen Air Excellent cut quality and speed Very little dross Not recommended Not recommended
Nitrogen Carbon Dioxide Fair cut quality Some dross Excellent parts life Good cut quality Excellent parts life Excellent cut quality Excellent parts life
Nitrogen Air Fair cut quality Some dross Excellent parts life Good cut quality Excellent parts life Good cut quality Excellent parts life
Nitrogen Water Fair cut quality Some dross Excellent parts life Excellent cut quality Excellent parts life Excellent cut quality Excellent parts life
Argon Hydrogen Nitrogen Not recommended Excellent on thicknesses above 1/2″ Excellent on thicknesses above 1/2″

 

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