Copyright Goodheart-Willcox Co., Inc. 414 Fluid Power periods of high air use, the higher pressure drop pro- duced by the venturi causes the spring-loaded bypass valve to open. This allows a portion of the system air to pass directly into the supply line. The unlubricated air that bypasses the venturi is mixed with lubricated air before being passed out of the lubricator outlet port. This air contains less oil than normal, but does provide adequate component lubrication during brief periods of high-air-volume operation. Lubricator selection Factors that must be considered when selecting a lubri- cator for a system are: • Conductor connection size. • Oil reservoir capacity. • System pressure drop created by the volume of air that must pass through the unit to operate the components of the workstation. Manufacturer information and specifi cation sheets supply these types of detail for the various models produced. 16.4 Distribution System Conductors and Fittings Moving compressed air from the compressor to the point of use at the workstation is a critical part of any pneumatic system. Any reduction in pressure between those points represents a loss of energy, which cannot be recovered. Previous sections of this chapter discuss general styles of distribution systems and their layout. This section is devoted to information about the pipe, hose, and fi ttings that form these systems. The volume of products and variety of available designs can make the expansion of an existing system or the development of a new system confusing. The following materials provide general guidelines and suggestions for the selection of appropriate conductors and fi ttings required for installation. 16.4.1 Rigid Conductors Pipe is the most common rigid conductor used for major compressed-air-distribution systems. Steel, cop- per, and ridged-plastic tubing may be found in smaller systems and on air-powered machines. Some of these materials may not be recommended for all installa- tions, but they may provide adequate service in some installations. However, the conductor must be cor- rectly rated for pressure and protected from external abrasives and activities that could crush the lines. When constructing or modifying a distribution system, pressure losses caused by system lines should During operation, system air passes through the lubricator inlet port and passageway leading to the reservoir. The venturi in the passageway creates a reduced pressure. This causes oil to move through the siphon tube and enter the airstream through the oil- drip orifi ce. The rapidly moving air breaks up the oil drops into a mist that passes with the system air into the reservoir airspace. The airspace reduces turbulence in the air/oil mist. This allows larger droplets of oil to return to the oil supply. The oil mist then moves to the outlet port and on to the workstation air supply line. The amount of oil added to the air is controlled by adjusting the size of the oil-drip orifi ce. During periods of low air use, all of the system air passes through the venturi of the lubricator. During Sight/feed dome Body Check valve Bowl Siphon tube Oil Drain (optional) Flow sensor Oil-drip orifice Metal bowl sight glass IMI Norgren, Inc. Figure 16-24. A lubricator atomizes a measured amount of oil and mixes it with the compressed air used at system workstations.