A spring brake actuator (1) for a vehicle, in particular a parking or emergency brake actuator, for use in a commercial vehicle, includes a cylinder housing (2) having a cylinder housing base (5) and a spring seat (7) on the base, a spring brake piston (9) located in the cylinder housing (5) for applying a braking force, and a compression spring (11) arranged between the spring seat (7) and the spring brake piston (9). The cylinder housing (2) is divided into a spring chamber (12) and a pressure chamber (14), the compression spring (11) being arranged in the spring chamber (12) and the pressure chamber (14) being supplied with pressurized fluid. An elastically deformable diaphragm (16) is sealingly mounted to the cylinder housing (2), with an inner periphery (18) sealingly mounted to the spring brake piston (9) to fluid-tightly isolate the pressure chamber (14) from the spring chamber (12).

An electropneumatic parking-brake valve unit for an electronically controlled pneumatic brake system has a first supply connection to a compressed air source. A spring brake connection connects to a spring brake cylinder of a vehicle. A parking-brake valve arrangement has a bistable valve switchable between switching states wherein a spring brake pressure can be controllable in dependence upon the switching state. A pneumatically switchable holding valve has a holding-valve connection for a first control pressure and the holding valve is connected between the first supply connection and the bistable valve. The holding valve is under a spring load into a first switching position wherein the bistable valve is connected to a deaerator. The bistable valve switches into a second switching position when the first control pressure exceeds a first threshold value. The bistable valve is connected to the first supply connection.

A spring brake cylinder is provided for brake systems of vehicles. It includes a spring brake piston, which is arranged in a housing of the spring brake cylinder and can be actuated by at least one accumulator spring and separates a spring chamber containing the accumulator spring from a spring brake chamber of the spring brake cylinder that can be filled with air for release and can be vented of air for application. A circulation device is provided at least for venting the spring chamber directly into the atmosphere. The circulation device is configured as a diaphragm valve device having at least one elastically movable outlet diaphragm and at least one elastically movable inlet diaphragm. The inlet diaphragm and the outlet diaphragm are in a closed position in contact with an associated valve seat in the home position of the diaphragms and, when a pressure difference between the spring chamber and the atmosphere exceeding a minimum pressure value is present, the diaphragms are moved into an open position lifted from the valve seat in order to build up and reduce pressure in the spring chamber.

A locking device configured to manually release a parking brake in a brake actuator for rail vehicles, the locking device including a spindle drive including a teething; a locking element engaging the teething of the spindle drive and switching a rotating movement and thus an axial force transmission of a parking brake on or off; and at least one contact damping element configured to dampen or prevent a contact of the locking element.