Quantcast HYDRAULIC SYSTEM.  (Figure FO-1)
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TM 10-3930-664-24 1-17. HYDRAULIC SYSTEM.  (Figure FO-1) a. The  hydraulic  system  controls  forklift  steering  and  provides  the  force  for  operation  of  the  mast  assembly. Hydraulic  oil  is  supplied  from  a  common  tank  and  pressurized  by  an  engine-driven  rotary  pump.    The  hydraulic  system consists of the following components: 27 gallon hydraulic tank Hydraulic fluid filter Engine-driven rotary pump Priority valve Orbital steering valve Steering selector valve Directional control valve Sideshift cylinder Tilt cylinders (2) Roll cylinder Mainlift cylinders (2) Freelift cylinder b. The   hydraulic   system   is   equipped   with   a   filter.      This   filter   is   designed   to   remove   any   fluids   or   solids suspended  in  the  oil  and  prevent  contamination  of  the  system.    The  filter  is  equipped  with  a  restriction  indicator  that indicates decreased flow through the filter due to clogging.  Should clogging occur, the filter’s bypass valve will actuate (25 psi) and allow oil to bypass the filter and continue on to system components. c. Oil  is  drawn  from  the  systems  hydraulic  tank  and  pressurized  by  the  hydraulic  pump.    Pressurized  oil  is distributed to the steering and mast components by an external pilot-operated priority valve.  The priority valve’s rated flow is 16 gpm with a relief pressure of 1500 psi. c. Steering  System.    The  steering  system  is  pressurized  by  the  hydraulic  pump  and  controlled  by  a  power- assisted steering wheel.  Hydraulic oil is drawn from the tank by the pump, passes through the system priority valve, and onto  an  orbital  steering  valve.    The  steering  valve  controls  the  flow  of  oil  to  the  steering  cylinders  in  response  to  the movement of the steering wheel. d. A  three-position  steering  selector  valve  allows  the  operator  to  select  the  steering  mode.    Forward  position directs hydraulic oil to both the front and rear axles for four-wheel steering.  Center position directs oil to only the front axle for traditional two-wheel steering.  Rear position directs oil to both axles for crab steering (allowing movement at an angle left or right). e. Steering cylinders in the front and rear axles control wheel movement.  Cylinder rod ends are attached to the left  and  right  wheel  hubs.    Cylinder  rods  turn  the  wheels  left  or  right  in  response  to  steering  wheel  movement.    The selection of two-wheel steering actuates only the front axle cylinder.  Four wheel steering actuates both the front and rear axle  cylinders,  directing  the  rear  wheels  to  turn  opposite  the  direction  of  the  front  wheels.    Four-wheel  crab  steering actuates both cylinders, directing all wheels to turn in the same position. f. Mast  Assembly.    The  mast  assembly  control  components  are  pressurized  by  the  same  system  hydraulic pump.  The Directional Control Valve located in the driver’s compartment controls the flow of hydraulic oil to the cylinders. 1-30

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