Abstract: A parking brake system for use on a railway car includes an actuator which is adapted to be attached to a service brake actuating lever arm of the railway car and to receive a flow of non-compressible holding liquid from a reservoir through a first valve unit. The first valve unit permits the liquid to freely flow to and from the actuator in a first position and only permits flow of the liquid towards the actuator in a second position. With this arrangement, movement of the service brake actuating lever arm automatically causes the actuator to be supplied with holding liquid from the reservoir, which liquid can be selectively retained by shifting of the first valve unit to the second position. Furthermore in accordance with the invention, the actuator can be shifted by supplying pressurized holding liquid thereto through the use of a motor driven pump circuit including a pressurizable reservoir.