Fluid is delivered under pressure by pump 1 to valve 2. Actuated by spring 3, spool 4 closes port a, and spring 6 actuates spool 5 to close passage d and open port b. The fluid forces back ball 7 and flows through pipeline f to accumulator 8. At this, rotary valve 9 is closed. Pressure increases in the system. Then fluid passing along passage k acts on spool 5, shifting it to open passage d and close port b. The fluid then passes through passage e into chamber m, shifting spool 4 to the position shown. This opens port a and fluid delivered by pump 1 is discharged to the tank. By turning valve 9, pipelines n and f, are connected together and fluid from accumulator 8 is delivered to hydraulic actuator 10, whose plunger rises to the required height. By turning valve 9 to its third position pipelines n and f are connected to the tank, the plunger of actuator 10 descends and the fluid is discharged through pipeline n to the tank. This reduces the pressure in the left-hand part of the system. Spool 5 is shifted to the left by spring 6, closing passage d and opening port b. Fluid from chamber m is discharged by spool 4 to the tank. At this, port a is closed and all the fluid delivered by pump 1 is admitted again into accumulator 8.
$4216$CHP,Dr$