By Reg Robinson

 I wrote this article because of my interest in having air horn on my truck and the lack of comprehensive information on such a project. There are posts wandering about the Internet on the results of someone's mod with a picture here and there but nothing that answered the many questions that I had nor anything that approximated a "how to guide". Even the company that supplied my kit offered little useful advice. I do apologize for the pictures since I wrote the article after the horns were installed so bear with me in the photographic aesthetics area. 

 Secondly let me state that this installation is about air horns. Those used in industrial applications. You know the big boys that use serious air. Not the plastic trumpets driven by those Coke can compressors. I have one in my Explorer and it doesn't even compare. If it comes from the local Auto parts store this article is probably not for you. 

 Further there are many variations of how to do things and I cannot cover every angle. I will state what worked for me.

 Let's begin.

The Cost

  The installation of these horns is expensive. Plan on spending several hundred to well over a thousand when all is said and done. There are places costs can be shaved and places it shouldn't. More on that later. 

The Parts

Horns:

I installed Nathan Airchime P3 horns on my F 350. These train horns cost a bit over $700. You can find train horns, marine horns, and such in many places. I have watched auctions and they all end at $500 to $1000 for a set of train horns. What do the letters and numbers for the horn mean? The P is the series of horn. Airchime made M, P and K series that I know about. I am not a serious train buff so if you want more information "track" down a train enthusiast site. There's a couple in the Yahoo Groups area. They also sell horns there. The bonus buying there is the knowledge and expertise from those with a passion for trains. The "3" means three trumpets or bells. Each is tuned to a different note. Airchime continues to manufacture K series and other horns for industrial applications such as mining. Those horns have a coverage of up to 6 kilometers and can put out 147 db at 1 meter.

 The M is an older series, has a mellower sound is rare and thus more costly. The K series is what you hear on modern locomotives. It is about the loudest horn out there putting out a teeth rattling 114 decibels at 100 feet. But volume has its price. They use lots of air. That is why I chose the P series. It was Nathan's most efficient horn for air usage and is more than loud enough for me. Efficiency is important to us because we are limited on air supply. 

 I also paid more because I bought from a business that refurbishes and sells these horns. 

Marine horns are another option. Buy what you like and will work for you. Think about mounting and function in making a decision.

 That plate supporting the horns is ½ inch thick steel. 

 

Air source:

 Something has to drive the horns. The choice is basically tanks or bottles. I'll mention the two then compare.

Air Tanks:

 The louder the horn and the longer you blast the more air is required. A small tank just won't maintain the sound volume for long. A few blasts and your done. The larger the tank the more time you have and the longer the sound can be sustained. I strongly recommend 5 to 6 gallons minimal. I installed twin 6-gallon tanks on the F 350. Even with the P3's a short blast drops pressure 5 to 10 psig. I bought my tanks, which came in a kit from groverairhorns. The price? $500+. But this included all hoses, fittings, pressure switch, inlet filter and compressor. Most everything is top shelf. I had problems with the fittings, which, I will mention later. 

 If you opt to shop around for a tank ensure it is in good shape, you know its history and it is pressure tested. Some machine shops will pressure test the tanks for you. Avoid anything that was picked up from a junkyard or other dubious origin. These horns operate around the 120-to150-psig range or higher and are going to be mounted on your vehicle possibly near vital lines. Don't go cheap here. Try to get tanks with a drain valve. Water will accumulate in the tank and this valve will make it much easier to get rid of it.

Compressed gas:

 Compressed air bottles are an option as a gas source. Bottle sizes vary. I have never heard of scuba tanks or fire and rescue (SCBA) style being used. Don't use propane tanks or anything that held a flammable or toxic gas. Using anything but compressed air is going to be costly and may change the tone of the horn due to the density difference of the gas. 

 Here's a letter sent to me from another member on a train horn site:

 Reg,

 "I have been told to expect to pay between $15 - $25 per bottle in an
exchange system, empty for full. One person uses compressed nitrogen at
2200psi and 142cuf volume. Bottle weight is 76lb empty and 90lb full. Aluminum
bottle types are available and are far less weight than the steel ones. You will
need a regulator to attach to your bottle in order to control flow to your horn.
I employ a standard Graham White modulating horn valve and it works excellent.
3/8" ID airline is a minimum requirement. I suggest an output of around 70psi -
100psi for plenty of punch. Blowtime per bottle depends on how much you want to
hear your horn - short toots will prolong a bottle's life greatly and long, 14L
type blasts will drain a bottle rather rapidly. At a horn honk event, I've
emptied 7 full bottles but got LOTS of sound in exchange.

As pointed out, the main goal is finding 'air' for the horn. Depending
on how much you blow, the Nitrogen system works great but is the most costly of
the current systems employed by several active group members. If you are
planning on doing a lot of honking, I would recommend a large air tank and a gas
compressor to get unlimited air. If you are just a casual honker, the Nitrogen
system works well, at least for me. I own 3 N2 bottles and currently exchange
them for around $48.00, all haz-mat, taxes and disposal fees included...they
usually last me a month to 6 weeks until I exchange them for another set of 3
full bottles.

Like I said, it all depends on how much you plan to honk your horns. Carrying
compressed gas cylinders is always considered hazardous and not recommended for
the general public. I've been learned on how to use these cylinders but only do
so during horn testing/recording or at a major horn honk event.

Pros: Quick, Convenient, Powerful & Easy to Use
Cons: Heavy, Bulky, Costly & Potentially Dangerous"

EM

Comparison:

Compressed air bottles work fine but, if you are like me you will have to have the tanks professionally refilled as mentioned in the letter. Basically once you run out you're out of the game until you can repressurized the tanks. Also if something happens and you develop a leak there goes the entire tank until the shop reopens. The larger horns gulp air down and a single compressed gas bottle with its regulator may or may not be able to keep up. Mine quickly outpaced the shop compressor, which puts out 6.3 SCFM at 90 psig. But it's a matter of how long you want to maintain the sound.

There are usage and transportation restrictions on compressed gas bottles that need consideration. Further I don't like the idea of 2500 psig of energy tucked beneath or behind me, especially in an accident scenario. I associate with a professional Firefighters and, provided a life is not in danger, none are willing to approach a vehicle in trouble if it has high-pressure gas on board. Also if you decide on compressed gas and use anything but air then do not route any pressurize lines inside the cab. A leak could be fatal.

Along with Mr. Marks comments the upside of using compressed bottles is a simpler installation as you do away with some hoses, compressor mounting and wiring, pressure switches and such.

My suggestion? I'd go with an onboard tank or tanks and a compressor. Why? As long as the atmosphere exists and you have battery power you have an unlimited energy source for the horn. Some setups can even run tools.

 This article focuses on a compressor setup. If you opt to use a compressed gas bottle and don't require a tank then the discharge of the regulator will attach to the SOV or manual valve.

 Here are my tanks. You can just see the second at the far end of the skid.

The Compressor:

 If you're not going the compressed bottle route then you have to put back in what you take out. For an occasional horn blaster like me the Viar compressor that came with the kits does fine. The horns can easily out run its low output, which is why I installed two 6-gallon tanks. However sounded horns like these is impressive. You only have to do it once. Trust me you won't want to do it a lot. There are much higher SCFM compressors out there made by manufactures such as Oasis. These things can operate air tools and could drive the horns directly but probably not at their recommended pressure. Also plan to fork out $1000+ for one of these. If you don't plan to run tools off the truck or have no need for such a beast the money can be better spent elsewhere. Like other modifications. The cost of the Viar? About $250.

 The intake for the compressor must be routed away from water. Mine is piped into the cab to take advantaged of dry air-conditioned air in Virginia's wet and humid weather.

 If you plan to install the compressor outside of the cab ensure it is spray and drip tight.

 Here's are pictures of the Viar. It is designed for exterior use. Tubing protection was later added to the black equalizing line in the photo on the right.

Pressure switch:

 Unless you want to manually turn the compressor on and off while staring at a gauge then you need one of these. In conjunction with a relay it cycles the compressor to maintain proper tank pressure. 

 This part is critical to safe operation of the system. The setpoint for the switch should not only be based on the horn's operation pressure but also should complement the compressor's output. That is, the switch should not be rated outside of the compressors range or safe operating pressure for the tanks. Mine cycles from 115 psig to 140.

 The brown material on the leads is electrical liquid tape.

Note the clear tubing protecting the gage line.

This is the front of the forward tank.

 

Hoses:

 Get the best quality you can buy. Buy new if possible. These lines are exposed to weather and often run beneath the vehicle subjecting them to various road hazards as well as vibration and rubbing. Ensure all are rated for the pressure.

The Valve:

 You need a way to sound the horn. Train engineers use a manual valve. The most common goes by the name of Graham White but that is for the purist. A manual valve simplifies the installation, provides a positive means to isolate the horn and allows variation of tone. It also means you have to find a way to run lines in and out of the vehicle as well finding a way to mount this valve. They aren't small or cheap. The prices I have seen are 100 to $150 for new or near new. I don't see why any plumbing ball valve wouldn't work. It won't be pretty but $5.00 vs. $150? Seems an easy decision for me.

 I use a fast acting SOV wired to a switch mounted on the cover below the steering wheel. The upside is a much easier time running wires vice hoses, it's cheaper at about $40 for the SOV and the sound is instantaneous. The down side is more electrical connections, water entrainment from the tanks and that all such valves have temperature limits. Mine is a GC 12 SOV. I contacted the company and they stated that although the valve is rated for freezing temperatures it could flow liquid O2 but that not recommended. I operate hundreds of these style valves at work and although I can't remember any failing due to temperature but it can happen. Having a valve supplying a horn stick open would be ugly. It is recommended that these valves be installed in the engine compartment for the heat.

 In Virginia the winters are often mild so mine is installed beneath the bed on the frame rail. 

 Extra wiring allows moving the valve w/o bleeding the system. The valve is angled to promote drainage.

The gauge:

< style="text-align: justify;"p>  You need to know what is going on so install a gauge. For convenience I ran a line inside the cab and have the gauge sitting below the dash and above the transmission hump. Protect this line wherever it enters the truck from rubbing. If this thing ruptures I hope your seats are vinyl because you will be cleaning them when you get back home.

Click here for part 2.