The input shaft (5) in the steering gear has a torsion bar (4). The torsion bar (4) connects the input shaft (5) and the main shaft (2). As the steering wheel turns, the input shaft (5) turns. The input shaft (5) moves the spool valve (1) according to how much the steering wheel turns. The spool valve (1) movement allows the fluid to flow. When the fluid flows the hydraulic pressure applies to the piston (3). The pressure applying to the piston (3) provides assistance to the steering effort.

When the steering wheel is in the straight-ahead position, the spool valve (1) does not operate. The power steering fluid flows from the power steering pump through the short-circuit back to the oil tank.

When the steering wheel turns to the right, the input shaft (5) pushes the spool valve (1) to the right. The spool valve (1) allows the hydraulic pressure to apply to the right side of the cylinder.

When the steering wheel turns to the left, the input shaft (5) pushes the spool valve (1) to the left. The spool valve (1) allows the hydraulic pressure to apply to the left side of the cylinder.