The integral piston power steering gearbox (fig. 8-28) contains a conventional worm and sector gear arrangement, a hydraulic piston, and a control valve. The control valve may be either a spool valve or a rotary valve depending upon manufacturer.

The operation of an integral power steering system is as follows:

With the steering wheel held straight ahead or in NEUTRAL position, the control valve balances hydraulic pressure on both sides of the power piston. Oil returns to the pump reservoir from the control valve.

For a right turn, the control valve routes oil to the left side of the power piston. The piston is pushed to the right in the cylinder to aid pitman shaft rotation.

For a left turn, the control valve routes oil to the right side of the power piston. The piston is pushed to the left in the cylinder to aid pitman shaft rotation.

In both left and right turns piston movement forces oil on the nonpressurized side of the piston back through the control valve and to the pump.

Figure 8-27.- The three major power steering systems. (A) Integral piston (linkage type), (B) External cylinder (linkage type), and (C) Rack and pinion type.

External Cylinder (Linkage Type)

The external cylinder power steering system has the power cylinder mounted to the frame and the center link. In this system the control valve may be located in the gearbox or on the steering linkage. Operation of this system is similar to the one previously described.