1. Rotary valve
2. Spool Valve 1. The Rotary Valves It is more commonly used. It uses a torsion shaft connected to the pinion gear to operate the hydraulic control valve. The operation of a power rack and pinion gear using a rotary type control valve. This design is normally used. 2. The Spool Valve It uses the thrust action of the pinion shaft to shift the control valve, the control valve can then route the oil to the power cylinder.