Timing Gears

in screw compressors of the dry type, the rotors are synchronized by timing gears. Because the male rotor, with a conventional profile, absorbs about 90% of the power transmitted to the compressor, only 1.0% of the

Figure 4-14. Timing gears for an oil-free heiicat-tobe compressor. Note the timing adjustment capability on the right side gear. (Courtesy ofA-C Compressor Corporation)

power is transmitted through the gears. The gears have to be of good quality both to maintain the timing of the rotors and to minimize noise. Because the compressor will turn in reverse on gas backflow, keeping gear backlash to a minimum is important. A check valve should be included in the compressor installation to prevent gas backflow. To control the backlash in the gears, a split-driven gear is used to provide adjustment to the gear lash and maintain timing on reverse rotation. To provide timing adjustment, the female rotor's timing gear is made to be movable relative to its hub. A close-up of a timing gear set is shown in Figure 4-14.

Timing gears are machined from low alloy steel, normally consisting of a chrome, nickel, and molybdenum chemistry. API 619 mandates an AGMA quality 12 gear, which is commonly used. The gears are of the helical type, which also help control noise. The pitch line runout must be minimized to control torsional excitation. The gears are housed In a chamber outboard from the drive end and are isolated from the gas being compressed.

Figure 4-14. Timing gears for an oil-free heiicat-tobe compressor. Note the timing adjustment capability on the right side gear. (Courtesy ofA-C Compressor Corporation)

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