Yoke actuating piston Pressure adjustment Compensator valve spring Control pressure (P$_{c}$) P$_{case}$ Pump yoke Yoke spring Drive shaft Compensator valve P s Case drain P$_{i}$ Outlet high pressure Inlet low pressure (P$_{i}$) Inlet pressure  (P s ) Outlet pressure  (P c ) Control pressure  (P$_{case}$) Case pressure Minimum stroke position Drive shaft Maximum pumping angle 12-22 Figure 12-31.  Yoke angle. Figure 12-30.  Normal pumping mode. at an outlet pressure that is equal to the pressure required on  the actuator piston to reduce the yoke angle to nearly zero,  approximately 1,100 psi. This depressurization and blocking  feature can be used to reduce the load on the engine during  startup and, in a multiple pump system, to isolate one pump  at a time and check for proper system pressure output. Flow control valves control the speed and/or direction of fluid  flow in the hydraulic system. They provide for the operation  of various components when desired and the speed at which  the component operates. Examples of flow control valves  include: selector valves, check valves, sequence valves,  priority valves, shuttle valves, quick disconnect valves, and  hydraulic fuses. A selector valve is used to control the direction of movement  of a hydraulic actuating cylinder or similar device. It provides  for the simultaneous flow of hydraulic fluid both into and  pump outlet. Outlet fluid is also ported to the blocking valve  spring chamber, which equalizes pressure on both sides of  its plunger. The blocking valve closes due to the force of the  blocking valve spring and isolates the pump from the external  hydraulic system. The pump strokes itself to zero delivery  Selector Valves Flow Control Valves Valves 