A pump assembly and a propulsion system that utilizes the pump assembly includes a casing defining an opening. The pump assembly also includes a first member at least partially disposed in the opening. The first member is movable linearly relative to the opening. The pump assembly further includes a biasing member disposed in the opening. The biasing member is movable independently of the first member. The first member is movable in a first direction that applies a load to the biasing member which creates a torque on the biasing member. The pump assembly also includes a second member that separates the first member and the biasing member such that the torque on the biasing member is transferred to the second member without transferring the torque to the first member when the first member applies the load to the biasing member.