How A Fog Machine Works

Since their introduction in the 1970s, fog machines have remained among the most commonly used piece of special effects equipment in the entertainment industry; including stage, film & television, and theme parks. Prior to the fog machines we use today, fog & smoke effects were created by incinerating flammable materials such as mineral oil and even used tires. Using a professional fog machine is a much safer and more effective way to create a smoke effect on set. Let’s take a closer look at how a fog machine works.

Every fog machine needs four essential elements to work:

• Heat Exchanger
• Pump
• Controls
• Fog Fluid

Different materials and components can be used to manufacture each element of the fog machine system. Changing a material, ingredient, or component of one element can affect the performance of the machine and the fog effect creates.

Heat Exchanger

When it comes to how a fog machine works – the number one element is the heat exchanger, which is a block of metal with a heating element inside. The temperature of the heating element is controlled by a thermostat to heat the entire block to a specific temperature. As the fog fluid comes into contact with the heat exchanger, it will vaporize immediately. The most commonly used metal in fog machine heat exchangers is aluminum. While aluminum heats quickly, it also gives up its heat easily. This necessitates proper engineering between the thermostat and the controls. Some professional fog machines are designed to make as much fog as possible until the temperature of the heat exchanger is too low, at which point it will switch off the pump and reheat. Others are engineered so that as the temperature of the heat exchanger cools, the pump slows down – enabling non-stop production of fog.

Controls

Once the heat exchanger on a fog machine has reached its peak operating temperature, something needs to switch on the pump. Professional fog machines feature multiple pump-control options. Almost every fog machine comes with a wired or wireless remote with some or all of the following features:

• On/Off Switch: a simple remote that provides an affordable option for making fog effects at “full blast.”
• Volume Control: regulates the speed of the pump in order to control the amount of fluid flowing through the heat exchanger, and thus, the amount of fog generated.
• Timers: allows users to create timed fog effects by using the remote to set a pre-determined “on time” and “off time” on the remote.

Most professional fog machines will also feature DMX capability that enables them to be controlled via a DMX control console. It’s also worth noting that many theme park attractions are controlled by 0-10V closed-contact controls. Some fog machines are also capable of integrating with this style of control system.

Pump

A fog machine pump moves the fog fluid from its reservoir to the heat exchanger. The proper pump must be selected in the design of the fog machine so that it matches up to the characteristics of the heat exchanger. If the fluid is pumped too quickly, for example, too much fluid will flow across the heat exchanger and cause it to cool down too rapidly. The most commonly used pump in professional fog machines for the entertainment industry is a piston pump. Along with efficiency, the piston pump has a long performance life and provides high-volume fog output.

Fog Fluid

A professional fog fluid is water-based with a small amount of either glycol or glycerin. When the fluid hits the heat exchanger, it is vaporized in a process known as “flashing” to create quick-cooling steam. As the fluid is flashed, it expands rapidly as it exits the machine. When the vaporized fog fluid mixes with the outside air, it instantly forms an opaque aerosol – which is the effect we refer to as fog or smoke. Varying the amount of glycol/glycerin in the fluid can affect the opacity of the fog effect – the more you use, the more opaque the effect will be. Different glycols and glycerins can also create different effects, such as quick-dissipating fog, for example.

Rosco received an Academy Award® for “the development of an improved, non-toxic fluid for creating fog and smoke for motion picture production.”

Using low-quality fog fluid can affect how a fog machine works. Manufacturers of professional fog fluid use deionized water to remove mineral particles that can clog up the fluid path through the heat exchanger. They also use high-quality glycols and glycerins. Rosco, for example, uses pharmaceutical-grade glycol to manufacture its range of fog fluids. When operating a fog machine, it is important to use a fog fluid that was designed specifically for that particular machine to maintain safety. Fog machines and fluids are designed as systems. Specific fluid formulas require specific temperatures for optimum vaporization. If a machine is calibrated at too low a temperature for a given fluid, the result can be “wet” fog that can leave behind a residue, or worse, spit hot fluid. If the temperature is too high, the fluid can “burn” or decompose, thus changing its chemical composition. This “burning” can create harmful byproducts

Rosco Vapour Fog Machines

Now that you know how a fog machine works, let’s use that context to explore Rosco’s range of Vapour Fog Machines. Every machine in the Vapour range features a piston pump, and gravity die-cast aluminum heat exchanger, but each machine is engineered differently to accommodate any budget or specification.

Rosco Fog Fluids

Rosco Fog Fluid: Creates opaque fog/smoke effects with an extra-long hangtime. This green-colored fluid features Rosco’s recognizable scent that helps audience and crew members understand that the effect they’re seeing is safe and not from an actual fire.

Stage & Studio Fog Fluid: Creates an opaque effect that dissipates quickly. This is useful for low-lying chilled-fog effects, steam effects, or for creating vertical “CO2 blasts” with the Vapour Plus.

Rosco Clear Fog Fluid: Creates the same long-lasting and opaque effect as Rosco Fog Fluid, but without the colorant and scent for people who may be sensitive to those ingredients.

Rosco Light Fog Fluid: Creates a long-lasting effect that is less opaque. This is useful for those that want to create translucent haze effects using a Rosco fog machine.

V-Hazer Fluid: Designed for use in the V-Hazer, this water-based fluid creates a smooth, long-lasting haze effect that won’t leave behind an oily residue on performers, set pieces, or equipment.