a tilt control valve controls the flow of hydraulic oil to actuate the tilt cylinders of a forklift mast . the tilt control valve is switched between two positions by the forklift operator by means of a tilt lever . when at one position , the tilt control valve stops flow of oil to the tilt cylinders , thereby prohibiting tilting of the mast . when at the other position , the tilt control valve permits oil flow to the tilt cylinders , thereby allowing tilting of the mast . a control valve is located between the tilt cylinders and the tilt control valve . a seat switch detects whether or not the operator is sitting on the seat . a cpu permits the operator to continue to operate the tilt cylinders to tilt the mast when out of the seat for a brief period . however , after the brief period , the cpu closes the control valve to prevent movement of the mast unless the operator has returned to the seat . when the mast reaches a predetermined maximum acceptable tilt angle , the cpu also closes the control valve , thereby prohibiting motion of the tilt cylinders .