Round Pyrathane® belts can be manufactured in any size from .062" (1.57mm) through .562" (14.27mm) in cross section. We manufacture belts in fractional, decimal and millimeter equivalents as well as O-ring size cross sections. The Pyrathane® belt size is designated by length rather than inside diameter. Our minimum length is 3-3/4" (95.25mm) in small cross sections. Larger cross section belts will have somewhat longer minimum lengths (see size chart). There is no maximum length limitation on the Pyrathane® round belt.
Round cross section Pyrathane® belts will run satisfactorily in either vee or round bottom pulleys. Vee bottom pulleys will, however, provide a much more positive drive than will round bottom pulleys because of the wedging action of the round polyurethane in the vee pulley. Vee bottom pulleys should be designed with approximately a 36 degree inclusive angle and should be deep enough so that the belt will not run on the bottom. Figure 1.
Round bottom pulleys may allow slippage in higher load situations which may or may not be desirable. Round bottom pulleys should be designed with a radius that matches the cross section of the belt being used. Figure 2.
We generally recommend the Pyrathane® belt be run under tension (see Stretch Recommendations); however, some applications may run satisfactorily when just the slack is taken up (under very little tension). An example would be when running in a vee groove where the wedging effect provides the driving grip.