A valve system includes a control module on a tractor portion of a vehicle adapted to receive a supply pressure as a control module supply pressure of the pneumatic fluid, receive a control module control pressure of the pneumatic fluid, and deliver a control module delivery pressure of the pneumatic fluid based on the control module supply pressure and the control module control pressure. A park control module selectively transmits the pneumatic fluid at the supply pressure based on a park brake control signal. A supply glad-hand fluidly communicates the selectively transmitted supply pressure of the pneumatic fluid to supply a brake on an associated trailer portion of the vehicle. A control glad-hand fluidly communicates the control module delivery pressure of the pneumatic fluid to control the brake on the associated trailer portion of the vehicle. An exhaust valve, which fluidly communicates with both the selectively transmitted supply pressure and the control module delivery pressure, exhausts the control module delivery pressure of the pneumatic fluid from the control glad-hand.

A method of brake control of a vehicle combination (2) composed of a tractor vehicle (4) with an electronically controlled braking system (5) and a trailer vehicle (6, 8) with a pneumatically controlled pneumatic braking system (7, 9), involves introducing the brake control pressure (p.sub.BC) of the trailer vehicle (6, 8) into a tractor brake control line (19) extending to a tractor vehicle-side brake coupling head (26) via an electronically controlled trailer control valve (13) of the tractor vehicle (4). At the beginning of a braking operation, a pressure pulse (34) exceeding a target brake control pressure (p.sub.BC_soll) is introduced into the tractor brake control line (19). The volume of a trailer brake control line (28, 29, 32) coupled to the brake coupling head (26) is ascertained, and the absolute value (p.sub.PI) and/or the duration (t.sub.PI) of the pressure pulse (34) introduced are/is established depending on the ascertained volume.

A control apparatus is configured to control a brake of a unit hauled by a vehicle. The vehicle includes a plurality of brakes for braking the wheels of the vehicle, a trailer brake for braking the hauled unit, and a parking brake for keeping the vehicle braked while it is stationary. The control apparatus includes a line for sending a fluid to the trailer brake through a control valve in order to brake the hauled unit in certain working conditions, a further line for sending a further fluid to the trailer brake in order to activate the trailer brake in other working conditions, and a valve device for controlling flow of the further fluid in the further line, the valve device being responsive to a signal indicative of the status of the parking brake.