TM 5-3825-226-24 HYDRAULIC SYSTEM GENERAL The   tractor   hydraulic   system   can   operate   either   a 613B scraper or 613B water distributor.  The function of hydraulic pumps and valves varies somewhat, depending on which machine is connected.  Differences are summarized in the following table: Water Tractor Scraper Distributor One hydraulic , elevator motor water pump pump drives motor Second hydraulic bowl cylinders lift cyl- pump drives (ejector and inders tractor steering door cylinders and also) Nomenclature  of  tractor  hydraulic  parts  is  based  on their  use  with  the  scraper.    That's  because  the  scraper was developed first.  However, it's easy to relate tractor parts  to  water  distributor  operation.    Simply  remember that the pump and valves that drive the elevator on the scraper operate the water pump on the water distributor. The pump and valves that drive scraper cylinders drive the  lift  cylinders  on  the  water  distributor.    For  ease  of understanding, water distributor nomenclature has been added    in    parenthesis    immediately    following    scraper nomenclature. The  motion  required  of  the  water  distributor  water pump differs from that of the scraper elevator.  For the water pump, no reverse motion or low speed    is    necessary.        Because    of    that,    the    tractor elevator circuit operates only in FORWARD direction at HIGH SPEED when a water distributor is connected. Another difference should be noted between operation  of  a  scraper  and  that  of  a  water  distributor. When   a   water   distributor   is   used.      tractor   lines   that would   feed   scraper   door   and   ejector   cylinders   are plugged off. OIL FLOW The tractor has two hydraulic pumps, located on the torque  converter  housing.    Each  is  a  two-section  vane- type  pump.    Oil  flows  from  the  pumps  to  valves  which control   water   distributor   or   scraper   functions.      The valves   are   actuated   by   levers   at   the   right   of   the operator's seat (in the tractor cab).  Flexible cables (with covers) connect the levers to spools inside the valves. When  the  control  levers  are  in  HOLD  position,  with the   engine   running,   all   oil   goes   through   the   control valves back to the oil filter in the hydraulic tank.  From there it passes into the tank. The oil filter has a bypass valve.  If the filter element gets too dirty, and the oil can not easily go through the element, there is an increase in the pressure of the oil to the filter.  High oil pressure opens the bypass valve and the oil goes through the open bypass valve into the tank. Cold  hydraulic  oil  can  not  easily  go  through  the  filter element.    The  increased  pressure  of  the  cold  hydraulic oil keeps the bypass valve open until the oil gets warm which decreases the oil pressure and closes the bypass valve. 5-3