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by the use of devices which dampen the vibration of the belts on
the slack side." Poly-V drive" is a single unit belt in which the
strength member covers the entire width of sheave and eliminates
V-belt matching and turnover.

Gears

Gears are used most where compactness of design, quiet
operation and large speed variations and ratios are required. There
are seven types of gears that are used in the oil fields. These are:
1. Spur gears
2. Helical gears
3. Herringbone gears (double helical)
4. Bevel gears
5. Spiral gears (including Hypoidi)
6. Worm gears
7. Rack and pinion.
Of these the helical and herringbone, and the bevel and spiral
gears are probably the most commonly used in modern drilling
equipment for power transmission and speed changing. The spiral
and bevel gears and their many derivations and combinations are
familiar in their application to rotary tables. The herringbone and
helical gears are used in many rig selective transmissions and mud
pumps, and more probably are used in pumping units than
anywhere else.
The herringbone gear is actually a double helical gear cut
together so that the end thrust obtained with a helical gear will be
cancelled out.
Alignment is extremely important and any gear installation
must be very rigid to forestall any working that might allow the
gears to get out of line. Dirty rough or operations involving severe
shocks are also quite bad for gear installations.
Gears usually are considered long-life installations if
properly engineered and maintained. Along with general

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