TM10-3930-660-34 CHAPTER 12 STEERING SYSTEM MAINTENANCE Section I DESCRIPTION AND DATA 12-1 This chapter covers maintenance procedures for the steering system components, as well as principles of operation. 12-2 PRINCIPLES OF OPERATION a.  System  Components  The  steering  system  components  include  steering  valve  (1),  steer  select  valve  (2)  and  four steering hydraulic cylinders (3) Additional, related components include the large (3 94 cu in ) section of dual gear pump (4)  and  priority  valve  (5).    Making  up  the  emergency  steering  system  are  an  electric  motor  driven  pump  (6)  and pressure switch (7).  Pressure switch (7) senses hydraulic pressure in the main steering circuit and closes to turn on the emergency   steering   pump   motor   and   a   warning   light   in   the   cab   when   main   system   pressure   drops   to   below approximately 75 psi b.  Normal System Operation Hydraulic flow from the large  section  of  dual  gear  pump  (4)  is  directed  to  the  inlet  port  of priority valve (5) The function of priority valve (5) is to ensure that sufficient oil flow goes to steering valve (1) to permit normal  steering  in  the  event  that  any  attachment  functions  are  being  operated  at  the  same  time  that  steering  is occurring.  The priority valve (5) will deprive the attachment functions of oil flow in order to maintain adequate flow for steering.  Component overpressure protection is provided by relief valve (8) which is built into priority valve (5). As long as the  steering  wheel  is  not  being  turned,  sleeve  and  spool  assembly  (9)  remains  centered  and  gerotor  (10) remains stationary.  Priority valve (5) will then direct pump flow to the main control valve The pressure resulting from the blocking condition  of  the  centered  steering  valve  sleeve  and  spool  assembly  (9)  keeps  priority  valve  (5)  shifted  to  the right (as shown) to permit flow to the main valve.  The steering cylinders (3) are held stationary by trapped oil in the lines. 12-1