Air System Install


Air. Nature’s best natural resource. You need it to live, your vehicle needs it to run and your onboard air system is no different. Unlike the air we breathe, the air that your onboard air system needs requires immense pressure in order to work correctly. Regardless if it's for blowing horns, airing up tires, powering air suspension or something else, you need air pressure in order for anything to work.

We use it every day when we drive our vehicles and honk our horns, but just because we depend on it doesn’t always mean you know how it works. This week, we get into the science of what air pressure is, how it works and (more importantly) what it all has to do with yourtrain horn kit or onboard air system.


To understand how air pressure works and how it affects your onboard air, you must first understand what air is. Well, hopefully, you don't need us to tell you what air is, but what does it consist of? Here is a refresher for any of you that slept through 8th-grade science class. Air is actually a collection of gas molecules(oxygen, nitrogen, carbon dioxide, hydrogen, etc.). While air is something that you can’t see or touch, it actually has a weight to it.

Gas Molecules

As the amount of these molecules in an area increases, millions of collisions occur on the surface area. These collisions are what we call air pressure. Air pressure is a measurement of the number of molecule collisions within a determined surface area. We measure these collisions with a barometer and count them in units of Pounds per Square Inch (PSI).

We can see examples of PSI all throughout nature. In fact, a human’s cardiovascular system has a pressure of 2.5-3 PSI depending on how healthy you are. The earth has an atmospheric pressure of 14.7 PSI at sea level. Examples of PSI are even more prevalent in man-made objects, such as a football or basketball, your shower, and scuba gear. A ton of our technology utilizes air pressure to make our lives easier.

Pressure may be utilized more in the automotive industry than anywhere else. Several systems in your vehicle depend on the pressure (PSI) being just right in order to work correctly. If your tires don’t have pressure, you’re not going anywhere. If you have a diesel engine, your turbo creates boost which is air pressure that is forced into the intake. Understanding what pressure each system needs to be is an important part of vehicle maintenance no matter what you drive. Your onboard air system is no different. Without proper air pressure, your onboard air system becomes inoperable.


It's our belief that every vehicle should have an onboard air system, no matter what kind of vehicle you drive. Having a louder and safer horn while having access to air to top off tires or fix a flat is just a good idea no matter who you are. Just like any other system on your vehicle, you need to at least have a rough idea of how it works and how to maintain it in order to get the most out of your onboard air.

The first thing you need to figure out is what you will be using your onboard air for. Are you using it for just the horns? Are you focused on mainly air suspension? Maybe you just need it in case you need to air up a flat. Onboard air systems and air source units come ready to work at all different kinds of pressure levels. For a small horn, you may only need a 100 PSI system to honk it effectively. To air up big truck tires, you may need a system that can output 200 PSI or more.

After you have your onboard air kit that works best for what you are going to be using it for, good to get yourself familiar with a few parts that are paramount to producing and maintaining air pressure in your system. There are four main components that you want to be aware of in order to make sure your system is getting the correct pressure you want: The compressor, the pressure switch, safety blow-off, and your air gauge.


Your compressor is the machine that intakes air and pushes it into a vacuum to pressurize it. You can typically hear your compressor running (the nicer ones are quieter than the others). If you don’t have any air pressure in your tank and you don’t hear your compressor kicking on, you probably want to check your compressor. The compressor is controlled by your pressure switch

Your pressure switch senses the air pressure in your tank and tells your compressor when to turn on and turn off. Your pressure switch will have a pre-determined “on” and “off” pressure. For example, on most of our larger train horn kits, we run a 110-145 PSI pressure switch. The compressor will turn on when your pressure falls below 110 PSI. When the pressure reaches 145 PSI it will automatically turn off. You can actually change what pressure your system runs at just by switching out your pressure switch. Just make sure that if you are going to a higher pressure, your compressor and your tank is rated for that higher pressure.

If your pressure switch fails to shut off your compressor and your compressor continues to run, your safety blow-off valve will activate to release excess pressure from the tank. While you should definitely have an air gauge on your system to tell you just where your pressure is, if you don’t have a gauge your safety blow-off activating is a way to know that your pressure is too high. Getting the right safety blow-off valve is important. If your safety blow-off is rated too low for your pressure switch, it will activate prematurely and you won’t be able to build pressure. Make sure your safety blow-off is always rated for a higher PSI than your pressure switch. For example, in most of our train horn kits, you get a 110-150 PSI pressure switch and a 175 PSI safety blow-off valve.

Your air gauge may be the most under-rated component on your kit. While it is true that you don't need an air gauge in your system in order for it to work, your air gauge is absolutely an integral part of your onboard air system. The fact is, if you don’t have a way to check your air pressure, how will you know if your system is working correctly? Any troubleshooting with onboard air usually starts with seeing what your air pressure is doing. Without a gauge, you just have no way of knowing what's going on inside that tank!


I’m sure we don't need to tell you that you need air pressure in order to honk your horns, but did you know that different types of horns require different levels of air pressure. As you probably know already, there are three main types of horns that you can have on your vehicle: Electric Horns, Air Horns, and Train Horns. All three types of horns can have different pressure requirements in order to sound off correctly. Knowing what pressure is best for your horn will ensure you are getting the full force of the blast every time you activate your horn.

Electric horns require the least amount of pressure in order to work. More than likely your stock horn is an electric horn. These horns require so little pressure, they don't even need an air tank to work and usually just come with a direct drive compressor. Since these horns are for lower pressure, you want to make sure you don’t attach them to an onboard air system that runs a high PSI. You can actually damage them by running too much pressure through them. For electric horns, its usually best to stick with the direct drive compressor that they come with.

Air horns and train horns run at a much higher pressure than electric horns. While some air horns do require a lower pressure than some train horns, generally the best pressure for most of our horns (air horns or train horns) are 150 PSI. From our single bell Safety Air Horn to the massive 5-chime Nathan AirChime Train Horn, the sweet spot seems to be 150 PSI for even our loudest horns. In fact, if you remember from last week's blog, we had some of our horns 3rd party tested for volume a few years back. We actually tested our Shocker XL Train Horn (our 2nd loudest train horn) at three different pressure levels. We tested them at 100 PSI, 150 PSI and 200 PSI and what we found even surprised us. The Shocker XL Train Horns were loudest at 150 PSI! Having more pressure doesn't always mean more volume for your horn, so keep this in mind when choosing an onboard air system. If you need to run at 200 PSI, your horn may not be as loud as it could be!

Once you have onboard air on your ride, you won't ever want to be without it again. If you have ever been stranded on the side of the road, you know how handy onboard air can really be. There is a reason why service trucks and emergency vehicles have an onboard air system. You can run powerful air tools off of it, blow up inflatables and even clean out your car with it. Understanding how your system works and how air pressure affects its performance will make sure you are never without air again!