An improved pistonless cylinder, including both single acting and double acting configurations, based on an Aramid fiber reinforced elastomer tubular which is highly stiff in radial direction against radial expansion and elastic in axial extension, so as to form a completely sealed, extendable and retractable pressure chamber and to be able to perform as well as, or better than, most of the conventional hydraulic cylinders in terms of load bearing capacities, maximum stroke distances and service durability. This improved cylinder employs no piston, piston rod, sealing seals or oil based hydraulic fluid, and utilizes non-metal materials to construct the majority of the parts for its extendable and retractable pressure chamber; therefore, this new cylinder can achieve significant weight and fabrication cost reduction. In addition, this new pistonless cylinder uses ordinary liquids, e.g., fresh water or seawater, as its hydraulic fluid, and can work directly as a hydraulic or pneumatic cylinder interchangeably without a need for much, if any, modification.