How do we determine how much duty cycle we will need?
That's a really good question. This depends how often the compressor will need to come on and how long the compressor will need to run to fill your tank(s) from the cut-in pressure to the compressor cut-off pressure of your pressure switch. For example, let's say that a particular compressor takes two minutes to fill a 5-gallon tank from a cut-in pressure of 110 psi to a cut-off pressure of 145 psi. If we assume that the compressor is required to continuously run the fill cycle five times, then we are looking at 10 minutes of run time, so that is two minutes multiplied by five times. Let's say after you run the compressor continuously for 10 minutes, you would anticipate a rest time of about half an hour, then you are looking at a requirement for a minimum of 25-percent duty cycle-rated compressor. This is figured by taking 10 minutes of run time divided by 10 minutes of run time plus 30 minutes of rest time equaling a 25-percent duty cycle. Remember that duty cycle is rated at 100 psi, so the 25-percent duty cycle requirement that we have calculated based on a cut-in of 110 psi and a cut-off of 145 psi should be considered as the absolute minimum duty cycle requirement for that particular application. It is a good idea to go a bit overkill on your duty-cycle requirement, which means that you should buy a compressor that has a slightly higher duty-cycle rating than what you require.
There are quite a few 100-percent duty-cycle compressors out on the market today. Does a compressor that has a 100-percent duty cycle mean that I can run the compressor all the time, 24/7?
This is a often general misconception, and the answer is no, you can't. You have to remember that duty cycle is rated at 100 psi at an ambient temperature of 72 degrees Fahrenheit, but certainly a 100-percent duty cycle compressor can run for much longer periods of time than a 30-percent duty-cycle compressor under similar conditions.
Does it matter where we install the compressor on the vehicle?
This depends on several factors, such as the available space, whether or not the compressor is a sealed or vented type, as well as personal preference and aesthetics.
Wait, you just mentioned sealed versus vented-type compressors. What's the difference? Can you elaborate more on those?
A compressor that is sealed is moisture- and dust-resistant. This type is obviously a compressor that has no vents. A vented compressor has vents throughout the motor housing and sometimes comes with a cooling fan
in the rear of the motor.
So, a vented type of compressor runs a lot cooler then, right?
Exactly! A vented air compressor delivers a higher duty cycle than a sealed compressor, since heat buildup more readily dissipates through the vents.
If a vented air compressor will give me a higher duty cycle, then what's the advantage of even considering a sealed-type compressor?
The preference of a sealed-type compressor is because of the fact that in mobile pneumatics, compressors are likely to be exposed to outside elements. High-performance 12-volt compressors are often sealed against moisture and dust to ensure a prolonged life for the compressor.
OK, but when is a vented compressor more suitable for use?
Vented compressors can only be installed in an area that is protected from the elements, such as inside a truck's bed when the area is covered, like when you use a tonneau cover on your truck.
That makes a whole lot more sense. So, if we need to install our compressor, say, next to our framerail, we should only consider buying a compressor that is sealed against moisture and dust, right?
Yes, and it is a good idea to route an intake filter away from and up to an area where it will draw in cleaner and dryer air if you are able to have a remote intake filter from