Compressor gear drives
In motorized drives, the gear unit is used to reduce speed and increase torque for the subsequent transformation of rotational motion into reciprocating linear movement.
Basically, it is possible to distinguish between external built-on gear boxes and gear units integrated into the pump drive housing. The use of an external gear unit depends on the manufactured number of pumps within a certain performance class. If the number of pumps is relatively low a more design-intensive integration is not worthwhile but a purchased external gear unit will be, despite the fact that this requires more effort per pump and more space. The external spur gear is preferred if the power to be converted is comparatively high, since it shows less wear and less power loss compared to the worm gear due to its basic design.
External gear units very often are spur gears in their own housing. They are mounted and aligned with the driving motor and the pump drive unit on a base frame and usually connected by shaft couplings.
Internal gears usually are worm gears. While they exhibit slightly poorer efficiency they do offer a large reduction ratio in the range of i=5 to i=50 in one single step and run with very low noise. Due to the relatively large sliding motions in the gear tooth system the worm wheel is made of bronze. This means that worm wheels can be operated continuously for many years even at varying speeds if designed appropriately and lubricated by proper gear oil. Figure 1 shows a worm shaft and worm wheel.
Figure 1: Worm shaft and worm wheel
Integrated spur gears, bevel gears, hypoid or crown gears are rare because these have smaller reduction ratios and are relatively expensive with low number of pieces and high outputs.