With more customized trucks running the streets with air-adjustable suspension setups than ever before, there is often widespread misinformation given about the need to adequately equip your air-suspended vehicle. Recently, we were able to get one of the fastest movers in the compressor market to stop running long enough to jot down some of the most common questions he receives regarding compressors and their proper use. Sammy Chu, president of Viair Corporation, is kind enough to lay it all out for us in pretty simple terms. If you haven't guessed it yet, Viair makes its own line of 12-volt automotive compressors that outperform just about anything in the market and takes the poundings that we mini-truckers dish out on a regular basis due to our demanding suspension systems. Read on to find all of your answers to your questions by one of the most knowledgeable persons in the world of compressor technology.
For more information, please call Viair Corporation. Its information is listed in the source box of this article as well as in its ad that runs in MT each month. - Editor
How do we choose a compressor that is fast enough for my setup?
The bigger the tank, the more airflow is required from the compressor to charge the tank. As a rule of thumb, for each gallon of tank capacity, a minimum of 0.15 cfm at 100 psi is recommended. This means if you have a 5-gallon tank, you need a compressor that puts out about a minimum of 0.75 cfm at 100 psi (0.15 cfm times five equals 0.75 cfm) for the compressor to recharge the 5-gallon tank in a reasonable amount of time.
What is cfm?
The notation cfm (cubic feet per minute) refers to a volume of air produced by the air compressor at a given pressure or psi (pounds per square inch).
What size air tank should we use? Is one tank enough to suit my needs?
In general, tanks that are smaller than 3 gallons are normally used in air-assisted types of suspension setups. For full-function air-suspension systems where air replaces the use of conventional springs, a 5-gallon or higher volume tank is recommended. More than one large tank may work better to suit your needs, though.
You said to look at a compressor's flow rate at 100 psi, but why not look at a rate at 0 psi?
Well, cfm at free flow (zero head pressure) is a good reference point, but it does not really tell you the whole story. When you decide to purchase a car or truck, do you ever ask the salesperson how fast the engine will rev while standing still? It is also helpful to get tank fill rates from your compressor supplier.
What is duty cycle?
A compressor's duty cycle determines the percentage of run time in a full cycle. A full cycle is the compressor run time plus rest time. Duty cycle can be a bit tricky in mobile pneumatics (automotive applications), since we are dealing with a wide range of conditions, applications, and ambient temperatures. Taking into consideration the above, manufacturers generally rate compressor duty cycles at 100 psi at a standard ambient temperature of 72 degrees Fahrenheit. This means a 20-percent duty cycle-rated compressor can run for five minutes (at 100 psi and 72 degrees) and then need to rest for 20 minutes. Five minutes of run time divided by five minutes of run time plus the 20 minutes of rest time equals a 20-percent