Spring-force applying means

Claim 1

In a spring-force applying means comprising a housing member having an outer cylindrical shell and a hollow, elongated trunk portion of reduced radius relative to the shell, first and second relatively displaceable members at least partially located within said housing member, a force transmitting element located at least partially within said trunk portion, a spring which exerts the force thereof across said first and second members so as to cause relative displacement between said members in one direction and to thereby enable the spring to apply a force to said force transmitting element, and a fluid pressure responsive member located within said housing member which, responsive to a predetermined differential fluid pressure thereacross, exerts a force opposing the force exerted by said spring so that said first and second members are relatively displaced in a direction which is opposite to said one direction such as to at least partially relieve said force transmitting element of the force applied thereto by the spring, the improvement wherein said pressure responsive member includes a tubular portion sealingly slideable within said trunk portion of the housing member, the force transmitting element being contained at least partially in said tubular portion, said spring-force applying means further comprising a force applying element separate from, and capable of movement relative to, said pressure responsive member and said force transmitting element and contained at least partially within said tubular portion, said force-transmitting element including means for providing, in a first angular relationship between said force transmitting element and the force applying element, mutual engagement with said force applying element so as to enable transmission of the force of the spring and for providing, in a second angular relationship between said elements, mutual disengagement of said elements so that the elements are axially movable at all times, one with respect to the other, and are unable to transmit the force of the spring, and means operable from externally of said first and second members for engaging said force applying element to effect such mutual disengagement of the elements, said force applying element including an abutment face which in the first angular relationship is engaged with a corresponding abutment face on the force transmitting element, and the force applying element including at least one internal spline which provides said corresponding abutment face at the end thereof and in the second angular relationship is engageable with a corresponding end of an external spline on the force transmitting element.