Abstract: A control valve for use in a tow vehicle-trailer braking system has a first bore connected to a master cylinder and a second bore with an entrance port connected to a pump in the tow vehicle for receiving a fluid under pressure, an exit port connected to a power steering control operated by the fluid under pressure, and a control port connected to a servomotor in the trailer. A first piston is located in the first bore and a second piston is located in the second bore. A lever which is located on a pivot pin connects the first piston with the second piston. When the operator applies a braking force to operate the master cylinder, the first piston receives a hydraulic force which acts on the lever to move the second piston and direct a portion of the pump fluid under pressure from the exit port to the control port to activate the servomotor brakes in the trailer.