The spray foam machine is often referred to as a:

• Proportioner
• Metering unit
• Proportioning Pump

They all mean the same thing. The foam machine’s sole purpose is to pump/deliver the materials separately out to the spray gun. During this process, the materials travel through their own sets of inlet filters, metering pumps, and high efficiency electric heaters, before entering the heated hose system.

Close-up view of an Opposed Piston Proportioning Pump

Proportioning machines come in all shapes and sizes from several manufacturers. There are several major distinctions to consider when specifying and purchasing a machine: type of drive system, output and pressure capacity, heating capacity, and electrical system are the majors. Maximum and minimum hose lengths may be affected by the choices made in these major component areas.

The drive system is what forces the metering pumps to go up and down, or back and forth. The metering pumps are the pumps that proportion, or ratio, the materials and move them out through the machine and hoses to the gun. Most drive systems are pneumatically, electrically, or electric-hydraulically driven. Pneumatically driven machines are typically less expensive, but because air is compressible, hydraulic drives are considered to be of higher performance.

Output & Pressure Rating
A machine’s output rating is a measurement of how much mixed foam the machine will dispense in any given time period. Output is typically classified in pounds per minute, gallons per minute, or kilograms per minute. The machine’s pressure rating is a measurement of how much pressure the machine will help to generate to mix the chemicals at the spray gun*. Pressure is typically classified as pounds per square inch (psi.) or bar for metric pressure measurement. Keep in mind that equipment manufactures often classify their machine’s maximum pressure rating as a static pressure. Operating pressure is often less than what is rated. It is important to make sure that your spray gun’s output and pressure ratings are matched to your machine and the type of work you want to do with your spray foam equipment.

* High Pressure Impingement Mixing
Most lay people think that the machine or metering pumps create the pressure at the gun. The pumps create material flow. Pressure is created by causing a resistance to flow. Much like using a garden hose to water your plants, you put your thumb over the front of the hose to increase the pressure to make the water spray further. Your thumb simply restricts, or resists the water flow, hence creating more pressure. This is the same role the spray gun plays in the spray foam scenario. The gun is essentially your thumb creating a resistance to flow from the machine, in order to create impingement pressure for the A-side and B-side materials to mix together. The gun also uses additional components that make the spray pattern a little better and more consistent than your thumb does.

Primary Heaters and Heating Capacity
Most spray foams are commonly processed at 120°F-140°F. The reason foam materials are heated is to lower the viscosity of the liquid chemical components to assist in pumping and mixing. Often times the temperature of the material can affect spray pattern development and the physical properties of the finished foam product, so it is very important to assure the machine’s primary heating system is in good working order, and of enough capacity to keep up with the output of the machine.

There are many types of engineered pre-heaters, or primary heating systems in use. Depending on the machine model and the manufacturer, you will most commonly see one of three designs:

• Direct Contact Heaters
• Indirect Mass Style Heaters
• Hybrid Direct/Mass Heaters

Direct Contact Heaters are just that. The material flowing through them comes in direct contact with the liquid. These use powerful electric heating rods, or “fire rods” directly immersed in the individual a-side and b-side components using a tube/shell design. They are virtually instantaneous, and will reach their 120 degree plus set points very fast.

Direct Contact Pre-Heater for Foam Equipment

Mass Style Indirect Primary Heaters use the same type of electrical heating rod to generate the heat for the system, but the heating rod is placed in a block of aluminum, instead of directly into the materials. The aluminum heating block has paths for the liquid to pass through it and the heat is passed through the aluminum block to the liquid in a conductive nature.

The Hybrid Style Heaters use a large block of aluminum wrapped around a direct immersion style heat rod inside the liquids. This is considered the best of both methods and employs both direct contact and mass style for a more consistent liquid heating result.

The larger capacity, or wattage of the “fire-rods” and the length of the heater’s effective heating area, combined with the speed (machine output) at which the material is traveling through – determines the overall heating capacity of the particular machine.

Electrical System
Most proportioning machines have heaters and control systems which require an electrical connection. Hydraulic machines use an electric motor to power the hydraulic drive system, which also requires electricity. Proportioning machines can typically be ordered by the manufacturer to operate anywhere in the world. Common electrical voltages are single-phase 220v, three-phase 220v single phase and 380v. Know where your machine will be used and be sure it is compatible with the available electrical system. Different countries commonly use different electrical systems.

If you are using a generator in your mobile spray rig, you will need to make sure the generator’s electrical voltage/phase output matches your foam machine’s voltage/phase specification.

Main Console
Most every spray foam machine has an electric console where all the machine controls are mounted. The electric console usually contains several on/off switches for the various components on the machine. It also contains temperature controllers for the primary heaters and heaters and the hose heat system. Most foam machines also have a pump stroke/cycle counter, and an emergency stop button also located on the main console.