Compressed air is used to operate pneumatic systems within a facility, and it can be separated into three categories; the supply side, the demand side, and the distribution system. The supply side is the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air. They are generally located in a compressor room somewhere in the corner of the plant. The demand side is the collection of devices that will use that compressed air to do “work”. These pneumatic components are generally scattered throughout the facility. To connect the supply side to the demand side, a compressed air distribution system is required. Distribution systems are pipes which carry the compressed air from the compressor to the pneumatic devices. For a sound compressed air system, the three sections have to work together to make an effective and efficient system.
An analogy that I like to use is to compare the compressed air system to an electrical system. The air compressor would be considered the voltage source, and the pneumatic devices would be marked as light bulbs. To connect the light bulbs to the voltage source, electrical wires are needed which will represent the distribution system. If the gauge of the wire is too small to supply the light bulbs, the wire will heat up and a voltage drop will occur. This heat is given off as wasted energy, and the light bulbs will be dim. The same thing happens within a compressed air system. If the piping size is too small, a pressure drop will occur. This is also wasted energy. In both types of systems, wasted energy is wasted money. One of the largest systematic problems with compressed air systems is pressure drop. If too large of a pressure loss occurs, the pneumatic equipment will not have enough power to operate effectively and efficiently. As shown in the illustration below, you can see how the pressure decreases from the supply side to the demand side. With a properly designed distribution system, energy can be saved; and, in referencing my analogy above, it will keep the lights on.
To optimize the compressed air system, we need to reduce the amount of wasted energy. This can be caused from leaks or pressure drop. Leaks can be hidden and are typically located at connections within the distribution system. In a poorly maintained system, a study found that 30% of the compressor capacity is lost through air leaks on average. Even though leaks are the “silent killer” to a compressed air system, they can be found with the Ultrasonic Leak Detector.
Pressure drop is more of a wide range issue. It is based on restrictions, obstructions, and piping surface. Out of these, restrictions are the most common types of pressure drops. The air flow is forced into small areas, causing high velocities. The high velocity creates turbulent flow which increases the losses in air pressure. Flow within the pipe is directly related to the velocity times the square of the diameter. So, if you cut the I.D. of the pipe by one-half, the flow rating will be reduced by 25% of the original rating. Restriction type of pressure drop can be found in different forms like small diameter pipes or tubing; restrictive fittings like quick disconnects and needle valves, and undersized filters, regulators and valves.
As a rule, air velocities will determine the correct pipe size for the distribution system. It is beneficial to oversize the pipe to accommodate for any expansions in the future. For header pipes, the velocities should not be more than 20 feet/sec (6 meter/sec). For the distribution lines, the velocities should not exceed 30 feet/sec (9 meter/sec). In following these simple rules, the distribution system can effectively supply the necessary compressed air from the supply side to the demand side.
To have a properly designed distribution system, the pressure drop should be less than 10% from the reservoir tank to the point-of-use. By following the tips above, you can have the supply side, demand side, and distribution system working at peak efficiency. If you would like to reduce waste even more, EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side. This will include the EXAIR Super Air Knives, Super Air Nozzles, and Safety Air Guns. This would be the pneumatic equivalent of changing those incandescent light bulbs into LED light bulbs. If you wish to go further in optimizing your system, an Application Engineer at EXAIR will be happy to help you.
Pressure Drop Chart by Compressed Air Challenge Organization.