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TM 5-3810-306-20 HYDRAULIC CONTROL VALVE RELIEF SETTING CHECKS AND ADJUSTMENT TOOLS: Pressure gauge (0 to 5000 psi) General mechanic’s tool kit:  automotive (5180-00-177-7033) SUPPLIES: None EQUIPMENT CONDITIONS: None GENERAL: Relief  valves  are  checked  and  adjusted by  causing  a  given  circuit  to  reach  its prescribed  pressure  limit  (stall).    At  this point, the relief valve opens, returning oil to the reservoir.  Hydraulic motor circuits may be stalled by preventing rotation of the   motor   shaft   prior   to   actuating   the control  valve.    Cylinder  circuits  may  be stalled    by    extending    or    retracting    a cylinder to its limit of travel. By   placing   a   pressure   gauge   in   the proper  line  or  port,  a  pressure  reading will indicate the point at which  the  relief valve  opens.    The  needle  on  the  meter face  will  climb  until  it  reaches  the  relief valve  setting.    At  that  point,  the  needle will stop climbing and fluctuate, indicating  the  relief  valve  is  open  and returning oil to the reservoir. Correct relief valve adjustment is mandatory  if  any  hydraulic  circuit  is  to function   properly.      Settings   must   be within tolerances. Therefore, adjustment  should  be  made  using  the correct   equipment,   after   the   need   for adjustment has been established. The  hydraulic  system  utilizes  four  valve banks.    Each  valve  bank  has  one  main relief  valve  limiting  maximum  operating pressure   of   the   component(s)   in   that circuit. CAUTION Do not hold relief valve open for more than one minute at a time. NOTE Release    control    lever    after    taking each reading and while making adjustments. NOTE An accurate 0 to 5000 psi (0 to 34,475 kPa/345  bar)  pressure  gauge  should be used when adjusting relief valves. 1. ADJUST RELIEF VALVE (1). a.   Loosen locknut (2). b.   Turn adjusting screw (3) in to increase pressure or  out  to  decrease  pressure  to  obtain  desired relief pressure as indicated on pressure gauge. CAUTION Do     not     overtighten     the     adjusting screw (3) or locknut (2). c.   Hold adjusting screw (3) and tighten locknut (2). d.   Recheck pressure setting. 16-54

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