Figure 7-34. Electrical system schematic.  The hydraulic fluid is pumped through the system to an  actuator  or servo. A servo is a cylinder with a piston inside  that turns fluid power into work and creates the power needed  to move an aircraft system or flight control. Servos can be  either  single-acting or double-acting, based on the needs of  the system. This means that the fluid can be applied to one  or both sides of the servo, depending on the servo type. A  single-acting servo provides power in one direction. The  selector valve allows the fluid direction to be controlled.  This is necessary for operations such as the extension and  retraction of landing gear during which the fluid must work  in two different directions. The relief valve provides an outlet  7-32  Low-voltage warning light  ALT  To wing flap circuit breaker  Magnetos  Starter  contactor  Clock  Ammeter  Alternator  control unit  Circuit breaker (auto-reset)  Circuit breaker (push to reset)  Circuit breaker (pull—off,  push to reset)  Fuse  Diode  Resistor  Capacitor (Noise Filter)  To inst  LTS  circuit  breaker  FUEL IND. BCN PITOT PULL  OFF  STROBE  RADIOFAN LDG LTS  FLAP  INST LTS  STBY VAC RADIO 1  RADIO 2  RADIO 3  NAV  DOME  RADIO 4  G  F  B  Alternator  B  Master  switch  Pull off  Alternator field  circuit breaker  Flight hour recorder Oil pressure switch To fuel quantity indicators  To flashing beacon  To pitot heat  To radio cooling fan  To strobe lights  To landing and taxi lights  To ignition switch  To wing flap system  To red doorpost maplight  To low-voltage warning light  To instrument, radio, compass and post lights  To oil temperature gauge  To turn coordinator  To low-vacuum warning light  Switch/circuit breaker to standby vacuum pump  To white doorpost light  To audio muting relay  To control wheel maplight  To navigation lights  To dome light  To radio  To radio  To radio or transponder and encoding altimeter  To radio  P  R  I  M  A  R  Y  B  U  S  A  V  I  O  N  I  C  S  B  U  S  Low volt out  Power in  Sense (+)  Field  Sense (-)  Ground  Starter  Battery  A L T  B A T  + 60 - 60  -30  +30 0  M P  L  R  Battery contactor  Ground service  plug receptacle  CODE 