Why are some rotary pumps built with timing gears and others are not?
A. Timing gears are intended to synchronize the rotation of two separate rotors in pumps that use screws, gears, lobes or similar devices to move liquid through the pump. See Figure 3.16. The timing gears can be seen on the right hand end of the rotors. Figure 3.16. Two screw pump Some rotary pumps, such as sliding vane pumps, have a single rotor, and synchronizing two rotors is meaningless. Some two rotor pumps such as gear pumps rely on the driven rotor to drive the second rotor, and timing gears are not used. However, when pumping abrasive liquids the addition of timing gears will relieve the pressure between the meshing gear teeth in the pump and reduce wear. In this case the timing gears are moved out of the pumping chamber and sealed against leakage along the rotor shaft. Lobe pumps and some screw pumps cannot drive the second rotor from the first rotor and timing gears are then necessary. More detail on rotary pumps can be found in ANSI/HI 3.1-3.5 Rotary Pumps for Nomenclature,
