TM 10-3930-671-24 9.1. Power Steering System Relief Pressure Setting Description and Operation.............................................................. F-403 Relief Pressure Setting Check ....................................................... F-403 Description and Operation All  GPX  25E  trucks  have  a  hydrostatic  power  steering system, which is supplied with oil pressure from the main hydraulic system pump through a steering pressure relief (flow  control)  valve  to  the  steering  gear.    The  steering handwheel  operates  the  steering  gear  control  valve  unit which directs all flow to the two-way steering cylinder on the steer axle. The  steering  system  relief  pressure  is  controlled  by  the pressure relief valve which is adjustable. Steering    system    relief    pressure    should    be    checked frequently,    since    relief    pressure    settings    above    the specified values can cause failure of the hydraulic lines, seals  in  the  steering  gear,  and/or  ball  joint  breakage  on the steer axle. Steering System Relief Pressure Setting: 1200-1300 psi (8270-8960 kPa) Steering system relief  pressure  setting  may  be  checked using   a   MICO   QUADRIGAGE   or   with   a   conventional pressure gauge 0-3000 psi (0-20,700 kPa) . Relief Pressure Setting Check WARNING Do  not  use  your  hands  to  check  for  hydraulic  leakage. Use  a  piece  of  cardboard  or  paper  to  search  for  leaks. Escaping   fluid   under   pressure   can   penetrate   the   skin causing serious injury. Relieve pressure before disconnecting    hydraulic    or    other    lines.        Tighten    all connections before applying pressure.  Keep hands and body away from pin holes and nozzles which eject fluids under high pressure.  If any fluid is injected into the skin, it  must  be  surgically  removed  within  a  few  hours  by  a doctor   familiar   with   this   type   injury   or   gangrene   may result. Note • The  following  procedure  may  be  used  to check steering system relief pressure only. If  relief  pressure  is  not  correct,  it  may  be from   dirt   in   the   valve   or   worn   parts, including  steering  control  valve  and  main hydraulic  pump.    Generally,  if  the  relief pressure   measured   when   the   steering system  is   in   bypass   is   not   correct,   the pressure relief valve should be adjusted or replaced. • To  perform  this  service  procedure,  it  is recommended that you first: • Park  truck  on  a  level  surface.    Lower the upright. • Put blocks under the upright rails and raise the drive wheels off the floor. • Return   all   controls   to   neutral,   apply parking   brake,   and   turn   key   switch OFF, except as directed. This procedure requires installation of a pressure gauge at   the   gauge   port   of   the   main   hydraulic   pump,   and measurement     of     the     pressure     while     the steering handwheel   is   turned   fully   in   one   direction   to   put   the steering system in bypass. F-403