How to size compressed air piping?

Inadequate compressed air distribution systems will lead to high energy bills, low productivity and poor air tool performance. An analogy, the compressed air distribution system works as the same role as electrical wires in an electrical system, while the air compressor is considered as the voltage source, and the pneumatic piping devices are marked as light bulbs. If the wire gauge is too small to supply the light bulbs, the wire will heat up and the voltage will drop. This heat is given off as wasted energy, and the light bulbs will dim.

It is critical to have a properly designed distribution system either for compressed air system or for electrical system, energy can be saved, and keep the air tool working in an optimium condition.

Three demands are placed on a properly designed compressed air distribution system: a low pressure drop between the compressor and point of consumption, a minimum of leakage from the distribution piping and efficient condensate separation if a compressed air dryer is not installed.

Fixed compressed air distribution networks should be dimensioned so that the pressure drop in the pipes does not exceed 0.1 bar between the compressor and the most remote point of consumption. The pressure drop in connecting flexible hoses, hose couplings and other fittings must be added to this. It is particularly important to properly dimension these components, as the largest pressure drop frequently occurs at such connections.

The best solution involves designing a compressed air pipe system as a closed loop ring line around the area in which air consumption will take place. Branch pipes are then run from the loop to the various consumer points. This provides uniform compressed air supply, despite heavy intermittent usage, as the air is led to the actual point of consumption from two directions. This compressed air system design should be used for all installations, except if some points of large air consumption are located at a great distance from the compressor installation. A separate main air pipe line is then routed to these points.

The pressure obtained immediately after the compressor can generally never be fully utilized because the distribution of compressed air generates some pressure losses, primarily as friction losses in the pipes and due to the compressed air piping material.

In addition, throttling effects and changes in the direction of flow occur in valves and pipe bends. Losses, which are converted to heat, result in pressure drops.

The equivalent pipe lengths for all the parts of the installation are calculated using a list of fittings and pipe components, as well as the flow resistance expressed in equivalent pipe length. These "extra" pipe lengths are added to the initial straight pipe length. The network's selected dimensions are then recalculated to ensure that the pressure drop will not be too significant. The individual sections (service pipe, distribution pipe and risers) should be calculated separately for large installations. 

The most overlooked idea in compressed air piping layout and design is air velocity. Excessive velocity can be a root cause of backpressure, erratic control signals, turbulence and turbulence-driven pressure drop.

The British Compressed Air Society (BCAS) suggests that a velocity of 6m/s or less prevents carrying moisture and debris past drain legs and into controls.

A velocity greater than 9m/s is enough to transport any water and debris in the air stream. Thus, the recommended design pipeline velocity for interconnecting piping and main headers is 6-7m/s or less, and never to exceed 9m/s.

If you are designing a compressed air system, please get in touch with one of the Atlas Copco sales engineers to help design the best and most optimum compressed air distribution system that lowers your operating costs and improves productivity.