Trailer hub cap device

Claim 1

A hub cap device for a wheel and axle unit having a hub member comprising: a. a cylindrical housing having one end open for attachment to said hub member; b. a piston within said housing having a peripheral sealing means in sealing engagement with the inner peripheral surface of said housing; c. means for limiting the movement of said piston axially of said housing between a first inner position and a second outer position therefor, including a pair of projections axially spaced on the inner peripheral surface of said housing, d. means for filling said hub member with grease under pressure, e. means for yieldably urging said piston toward the inner position therefor to apply a positive pressure on the grease in said hub member, f. means for bleeding grease from said hub member when the piston is in the outer position therefor, g. manually operated means for adjusting the effective action of said yieldable means on said piston, adjustable to a first position wherein said yieldable means has a maximum effective action for urging said piston toward the inner position therefor and to a second position wherein the yieldable means is rendered ineffective to urge the piston toward said inner position therefor, and h. coacting guide means on said piston and on one of said projections for holding said piston against rotational movement within said housing, i. said piston, manually operated means, and yieldable means, when the yieldable means is in the second position therefor, being freely movable together as a unit axially of said housing between the inner and outer positions for said piston.