Train Horn Kit Glossary of Terms

Air Compressor The air compressors sold at are electro-mechanical reciprocal compressors and have two main components: an electric motor body, and a piston assembly. The electric motor runs on a 12volt power supply to drive the piston. These compressors are small and efficient and require very little routine maintenance.

Air compressors should always be run in parallel (no inlet port intakes compressed air) and never in series (the inlet port intakes air from a compressed system). The number of compressors in a system should be determined by the volume of air in the reservoir (air tanks and lines). There should always be at least one air compressor per every five gallons of air. recommends one compressor per every three gallons of air unless otherwise instructed or sold as a kit.             

Air Consumption The air consumption of a horn is the amount of air that a horn uses when sounding and is measured in CFM. The higher the value of this rating the more compressed air the horn uses per second.

When building an air system the air consumption of air devices should be a key factor in deciding what kind of capacity the system requires and how many compressors should be installed. High consumption devices should be paired with more efficient compressors and larger tanks.


Air Dump The air dump in a valve is the gate which allows air to flow through. Air dumps are rated in size and should match the size of the air line attached.

Air Filter/Air Inlet An air compressor air filter is a component used to prevent dust and debris entering the intake duct of the air compressor. This helps prevent abnormal wear due to foreign objects and increases the lifespan of the compressor.

The air filter/inlet's location is very important when choosing a suitable mounting place for any compressor. The air filter should always be placed and faced away from any source of debris, vapor, or liquid. An air compressor should never be mounted with its filter facing a tire. An air compressor cannot function while submerged and should never be placed where its air filter/inlet may become submerged.

Air filters should always be used in conjunction with an air compressor and should be changed regularly in relation to the usage of the air compressor. To properly maintain an air system, the air filter should be changed weekly and replaced if dirty

Air Horn An air horn is a horn powered by compressed air. Inside of the air horn compressed air is channeled onto a diaphragm, which resonates the air on its exit from the horn bell. Air horns are used in many applications such as police sirens, train horns, boat horns, emergency sirens, truck horns, and even some hand held canister horns.

Air System An air system is a system comprised of one or more air compressors, air lines and fittings, air tanks, pressure switches, air valves and an air driven device. These devices include air horns (truck horns, train horns, boat horns, etc), air tools (impact wrenches, air nail guns, feed sprayers, etc), air pistons (air bags, air jacks, etc).

Compressed air systems are used everyday in applications all over the world. From the air inside of car tires to the pesticides sprayed on crops, compressed air systems have become one of the most valuable technologies of the modern times and yet remain invisible to most.

Air Tank An air tank is a reservoir in an air system that collects a volume of compressed air. Air tanks are vital for any air application that has higher air consumption than compressed air production. All train horns consume large volumes of air and appropriately sized tanks should always be used.

The total volume of an air system is determined by the sum volume of all of the tanks in the system. Larger volumes take longer to fill and also longer to drain. Tanks should be chosen with concern to the size of the consumption device. Having a low volume of air and an air hungry device can lead to failure and disappointment.

Almost all air devices consume air much faster than it can be produced. Devices that can operate without an air reserve are specifically marked and should be accompanied by an on-demand compressor.

Air Valve An air valve is a mechanical valve in an air system that can be opened to allow air past. This device is normally used to allow compressed air to travel from the reservoir to an air device.

All air valves are electric solenoid valves and are triggered by an electrical signal attached to a switch. This allows the user to power any air device with the push of a button or the flick of a switch.

Burst Pressure The (maximum) burst pressure of a tank represents the maximum burst flow from connected lines. If the tank is allowed a burst of higher pressure than this rating it may become damaged and could become dangerous.

The burst pressure of a tank is often rated higher than its working pressure but it is never recommended to burst over the working pressure. Doing so increases the chance that the tank may become over pressurized and is dangerous both to the equipment and the safety of individuals.

CFM @ PSI This is a measurement of the compressed air volume being produced at different airsystem pressures. As the overall pressure (PSI) of the system (air in the tank) increases the volume output by the compressor (CFM) decreases due to resistance. This means that a system will fill much more quickly during low pressure.

These measurements are usually rated at 0PSI and 100PSI respectively. A measurement of only CFM always represents the 0PSI rating. The 0PSI rating is also known as free flow (no resistance) and outputs the most volume that the compressor is capable of in a standard environment. The 100PSI figure is often provided as a standard value used to determine the slow- down of a compressor's functionality at higher resistance.


Cut-Off Pressure The cut-off pressure of the switch is the pressure at which it stops relaying power to the compressor or any other device it is connected to. The cut-off pressure of a pressure switch should never exceed the working pressure of the compressor it is powering or any devices and components connected, or to be connected, to the system.

It is recommended to match the two pressures but it is possible to use a lower cut-off pressure than the powered compressor’s working pressure. The purpose of this could be to not exceed the pressure rating of devices connected to the system or to extend the compressors working life.


Decibal A decibel is a logarithmic measure of sound pressure. An increase of about nine decibels is roughly equivalent to doubling the amount of sound pressure. Decibels measure only the pressure of a sound wave and not its power. The power of a sound wave is roughly the square of its pressure.

The distance at which a sound can be heard depends on the direction of the sound wave, the power, and the volume. An air horn can have the same decibel rating as another but output a more focused or less focused wave. Larger horns produce less focused sound and output higher volumes so they can be heard from farther away and in less focused areas.


Diaphragm The diaphragm of a horn is a metal disc inside of the horn base which resonates the air passing through the horn. The type of material the diaphragm is built from is important to the construction of the horn. Metals that rust easily are undesirable since compressed air contains moisture naturally. Metals that are easily damaged are also undesirable since dust and debris may enter your air system and cause damage.

Duty Cycle The duty cycle (work cycle) of a compressor is a measurement of the compressors work time compared to its required rest time. The percentage given represents the working portion of this cycle. This required rest time of some compressors is due to heat produced during the duty cycle. The length of time of the cycle varies by compressor.

A lower duty cycle compressor will have a higher CFM output than the compressors of its class but will have a longer required rest time. A higher duty cycle compressor will have a lower CFM output but will have a shorter rest time.
When selecting a suitable compressor for an air system it is important to identify what duty cycle will be most efficient in the application. High CFM/Low duty cycle compressors will provide fast burst fills and are perfect for burst applications such as with a set of Maximus train horns. Low CFM/High duty cycle compressors provide a constant slow fill of air and are perfect for applications that need a constant supply of air such as air bag systems.


Frequency The frequency of a sound is a large factor in human perception of that sound. A high frequency sound is referred to as a high pitch sound or treble. A low frequency sound is referred to as a low pitch sound or bass.

Air horns very greatly in pitch. Multi-belled horns are tuned with a different pitch per horn. The frequency of a horn is very important when choosing the right air horn for any application.

Horn Train horns run the gamut of sizes and shapes. Separate trumpets are slim and can be up to two feet long. In an attached array, there are two trumpet horns, three trumpet horns and even four trumpet horns. It's generally believed that you need three or more trumpets ("bells") in the array to product as authentic train horn tone. Each trumpet sounds a different note. It's the combination of these notes that produce the distinction "blat" that immediately says "train horn."

The better train horns are made of metal. Plastic horns are OK in low priced value kits but they are not considered the "real deal" by most train horn enthusiasts. Steel, zinc, brass and copper are common metals. Horns are either chrome or gold plated or painted black. We do not sell plastic horns!

NPT Port NPT (National Pipe Threading) ports are standardized ports for water and air lines. NPT fittings must be used with NPT ports in order to have a working air system. Never mismatch fittings. This fitting standard is measured in inches and does not necessarily match the size of the airline attached. The airline attached is recommended not to exceed the size of the port.

Pressure Switch A pressure switch is a device used in conjunction with an air compressor to prevent the compressor from working above its maximum working pressure. The switch provides power to the compressor until its cut-off pressure is detected.

A pressure switch must always be measuring the same air system as the compressor it is powering. Pressure switches should always be fused properly.

SAE SAE (Society of Automotive Engineers) specifications on air tanks rate the maximum working pressure and burst pressure the air tanks can withstand. The SAE ratings should never be exceeded.

Solenoid Horns are activated by a solenoid valve. Horns (and compressors) are energized by a 12 volt source. The horn can be activated by your regular horn button or you can buy a new separate horn switch. It's all in the installation.

These are the basic components of any kit. You should receive enough air hose, fittings and hook-up wire to do the job. Don't be shy about having a pro do the job. Shops that specialize in aftermarket installations of sound systems and alarms would be an appropriate choice.

Start-Up Pressure The start-up pressure of the switch is the most pressure at which the switch will begin relaying power again after it is reached its cut-off. This pressure is usually about 40PSI lower than the cut-off pressure allowing the compressor attached time to cool down before resuming its duty.

Valve Case The valve case is the casing around the air dump. The strength of the case is important and it should be noted that different valves can withstand different working pressures.

Working Pressure The working pressure of a valve represents the maximum pressure in the air system that the valve can withstand without undesirable behavior. This pressure should never be exceeded. Exceeding the working pressure of a valve can damage the equipment and possibly cause injury.

Pressure Switches should always be used in conjunction with an air compressor and should always match the factory-rated working pressure of the compressor.