an inlet port of a manual timing valve is pressurized from a source of regulated line pressure through a manual valve when the vehicle operator selects certain gears manually . hydraulic flow through this port enters the manual timing valve through an orifice sized to control the flow rate . a first volume of the timing valve increases in size as a first piston moves due to pressure of fluid flowing to the valve through the orifice . pressure within the first volume is maintained constant while the first volume expands during a first interval , which ends when the first piston reaches the extremity of its motion . thereafter , pressure entering the valve through the orifice increases abruptly and causes a second piston to move against the force of a spring due to the increased pressure force developed on the second piston after the first volume stops expanding . as the second piston moves the size of a second volume increases during a second interval until the second piston bottoms . when this occurs , the valve opens a connection between the first port and an outlet port through a bypass line in which there is no restriction .