Bearings and seals in rocket engine turbopumps operate directly in the cryogenic propellant. Special design and lubricating techniques are required since ordinary oils and greases become glasslike solids at these extremely cold temperatures. The bearing load carrying surfaces are lubricated by thin transfer films. The lubricant is provided by the bearing cage which is usually fabricated from a self-lubricating Teflon compound. Material compatibility and wear are the important factors for face contact seals in these cryogenic fluids. Carbon, normally used in seal nosepieces, has violent reactions when run in liquid fluorine, an extremely chemically active fluid. Wear at the rubbing contact is minimized when the seal is designed for positive face separation with acceptable leakage.
