Our customer was using a urethane spool seal for a hydraulic control valve. A new design to the valve resulted in increased temperatures exceeding the capability of the urethane being used. Frictional forces needed to be kept as low as possible to prevent high shifting forces.
The new valve design resulted in increased fluid temperatures, so the current material was not sufficient and was deteriorating too rapidly. Low spool drag forces were required in conjunction with durability and high temperature capability.
HNBR was selected to overcome the temperature concerns while providing good durability and wear characteristics. A custom designed lip geometry was able to keep the drag forces down. All of this was done in the existing available space to allow for backwards compatibility so the customer didn't have to change any casting or groove geometry.