US Patent 8016300 Mobile cart having a retractable-wheel base system

A mobile cart for carrying a plurality of fluid canisters. The cart includes a platform configured to support the fluid canisters. The cart also includes a base having a base body and a plurality of wheels movably connected to the base body so that the wheels can be selectively moved with respect to the base body between an extended position and a retracted position. In the extended position, the plurality of wheels extends from the base body so the cart can roll, on the plurality of wheels, over the support surface supporting the cart. In the retracted position, the plurality of wheels is retracted relative to the base body so that the cart cannot roll, on the plurality of wheels, over the support surface.