Variable speed transmission

A transmission comprising a first adjustable rotary sheave including coaxial first and second flanges, one of said flanges being movable axially toward and away from the other of said flanges;

• a second adjustable rotary sheave including coaxial first and second flanges, one flange of said second sheave being movable axially toward and away from the other flange of said second sheave;
• at least one endless flexible torque transmitting element trained over said sheaves;
• a source of pressurized fluid;
• means for adjusting said first and second flanges of each of said first and second adjustable rotary sheaves;
• said adjusting means having at least two fluid receiving chambers and means for connecting at least one of said chambers to said source;
• and means for regulating the flow of fluid between said at least two chambers, including at least one annular sealing device;
• wherein said at least one annular sealing device has an annularly radially outer portion, an annular radially inner portion, and an annular intermediate portion disposed between and connecting said radially inner and radially outer portions with each other;
• wherein said radially inner and radially outer portions of said at least one sealing device extend in the direction of a common axis of said portions and said intermediate portion extends substantially radially of said common axis and wherein at least one of said radially inner and radially outer portions of said at least one sealing device has a plurality of reliefs spaced apart from each other in a circumferential direction of the respective one of said radially inner and radially outer portions.