TM  1-1520-240-10 2-6-2            2-6-5.  PWR XFER Switches. The two-position PWR XFER (power transfer) 1 and 2 switches are located on the UTIL (utility) hydraulic por- tion of the HYD control panel (fig. 2-6-1). Each switch is labeled ON and OFF. If either switch is ON, 28-volt DC opens the normally closed solenoid valve in the corre- sponding PTU and open a valve in the pressure control module. This allows utility hydraulic system pressure to operate the hydraulic motor pump on that PTU, pressur- izing the flight control hydraulic system. Consequently, the  flight  controls  can  be  operated  on  the  ground  for maintenance and checks without the rotors turning. When both switches ar ON, No. 1 and No. 2 flight control hydraulic  systems  will  be  pressurized.  Both  hydraulic motor pumps of the PTU’s supply pressure for flight con- trol operation, When the switches are OFF, the solenoid valves are closed and the flight controls cannot be oper- ated  unless  the  rotors  are  turning.  Power  for  these switches is supplied by the No. 2 DC bus through the HYDRAULICS PWR XFER circuit breaker on the No. 2 PDP. 2-6-6.  RAMP PWR Switch. WARNING When the RAMP PWR switch is at OFF, be sure  the  RAMP  CONTROL  valve  is  not moved  from  STOP.  Operating  the  valve from  STOP  to  UP  or  DN  may  cause  the ramp to free fall. The RAMP PWR switch is on the lower right side of the UTIL  hydraulic  portion  of  the  HYD  control  panel  (fig. 2-6-1). The switch has three positions labeled ON, OFF, and EMERG. At ON, the ramp isolation valve in the utility system pressure control module is open, allowing sys- tem  pressure  for  normal  ramp  operation.  At  OFF,  the ramp isolation valve is closed, isolating the ramp system from the remaining utility systems. This prevents loss of utility system fluid if the ramp system fails. At EMERG, electrical power is supplied to the RAMP EMER switch, allowing  the  ramp  and  cargo  door  to  be  opened  and closed  from  the  cockpit.  Power  to  operate  the  RAMP EMER switch and ramp isolation valve is supplied by the No.  1  DC  bus  through  the  HYDRAULICS  UTIL  SYS CONT circuit breaker on the No. 1 PDP. 2-6-7.  BRK STEER Isolation Switch. The BRK STEER isolation switch is on the HYD control panel (fig. 2-6-1). It is a guarded two-position switch la- beled ON and OFF. At ON, the brake and steering isola- tion valve in the utility system pressure control module is open, allowing system pressure for normal brake and steering operation. At OFF, the brake and steering isola- tion valve is closed, isolating the brake and steering sub- systems from the remaining utility systems. ON is the normal flight position. OFF is used when there has been a hydraulic failure in the brake or steering system. Setting the switch to OFF in this case prevents loss of system fluid. This allows the remaining utility subsystems to con- tinue to function normally. The brake system contains an accumulator which allows limited system operation in a hydraulic failure. The swivel lock system also has a small accumulator which keeps the swivel locks locked with the system  isolated.  Power  to  operate  the  BRK  STEER switch and valve is supplied through the HYDRAULICS BRK STEER circuit breaker on the No. 1 PDP. 2-6-8.  RAMP EMER Control Switch. WARNING The  RAMP  EMER  control  switch  is  in- tended  for  emergency  use  only  during smoke and fume elimination procedures. Inadvertent  operation  of  the  cargo ramp and cargo door from the cockpit may re- sult in injury to personnel or damage to equipment. The momentary, guarded, three-position RAMP EMERG (ramp emergency) control switch is located on the UTIL hydraulic portion of the HYD control panel (fig. 2-6-1). This switch allows the pilot, in an emergency condition, to raise or lower the ramp to a partially open, fully open, or fully closed position. The switch is labeled UP, HOLD, and  DN  (down),  and  is  spring  loaded  to  the  center (HOLD)  position.  the  switch  is  active  only  when  the RAMP PWR switch is set to EMERG. For up operation, the ramp will move only while the momentary switch is held  in  the  UP  position,  and  will  stop  as  soon  as  the switch is released. For down operation, the switch has a minimum 5 second function which allows the pilot to low- er the ramp for 5 seconds by momentarily moving the switch to DN and immediately releasing it. The down- ward ramp movement will stop 5 seconds after the switch is selected to the DN position (5 second timer circuit). If the ramp and cargo door (ramp tongue) are in the fully retracted into the ramp. The ramp can be further lowered in 5 second intervals, by momentarily reselecting the DN position when the ramp stops. The downward motion of the ramp may be stopped at any time by momentarily setting the RAMP EMERG switch to the UP position. The ramp can also be lowered continuously (for more than 5 seconds) by holding the switch in the DN position until the desired ramp lever is achieved. At the UP or DN position, 28-volt DC activates the re- spective up or down solenoid on the ramp control valve. The ramp control valve handle moves to the selected position, and the ramp repositions as selected. At HOLD, electrical power is removed from both the up and down solenoids. The ramp control valve handle moves to the STOP position and the ramp remains locked in position. Power for the switch is supplied by the No. 1 DC essential