Abstract: A single acting, spring return hydraulic cylinder suitable for use as an actuator of a portable cutter or the like. A piston slidably received in the cylinder has formed therein a hollow and a hole communicating the follow with a fluid chamber on one side of the piston. For discharging the fluid from the fluid chamber through a discharge port in one end of the cylinder upon full extension of the cylinder, a release valve mechanism is provided which comprises a valve stem slidably extending through the hole in the piston into the hollow in the piston, and a valve head formed on one end of the valve stem and received in the hollow in the piston. One or more expansions are formed in the piston for the admission of the pressurized fluid from the fluid chamber into the hollow in the piston during piston travel away the one end of the cylinder.