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Hydraulic System

G500 Systems

The G500 hydraulic system is another step in the evolutionary progress from the original G159 (landing gear, brakes, main entrance door), to the GII/III (1500/3000 psi flight controls added), to the GIV (3000 psi flight controls), to the GV (simplification of landing gear and flap hydraulic lines), to the G650 (fly by wire). ATA 29 covers most of what you need but does not touch on back up hydraulics for the flight controls; for that you need to visit: G500 Flight Controls.

Work in progress



How it works . . .


Electrical Interfaces

Work in progress

Hydraulic Lines

Work in progress

Controls

Work in progress

Operation

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Photo: G500 Hydraulic System, System Synoptic, PAS, p. 8-23

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Left System

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Photo: G500 Hydraulic System, Left System, PAS, p. 8-11

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[PAS, p. 8-2]

  • Independent.
  • The left system is independent and isolated from the right system.

  • Powered by.
  • It is powered by the left Engine Driven Pump which is mounted on the engine gearbox. This pump outputs a constant pressure (3,025 ± 50 psi), variable volume. The volume is low at idle, higher at cruise. The pump offloads when in flight if an engine drops below idle (< 55% N2), (automatically controlled by Electronic Engine Controller). This reduces pump outlet pressure so as to reduces drag on the engine during an airstart. The system has a pressure relief valve to relieves pressure during surges at 3500-3750 psi.

  • Reservoir.
  • The left hydraulic Reservoir is larger than the right and is considered full at 2.5 gal. It supplies hydraulic fluid for: Left Engine-Driven Pump, Aux Pump, PTU Pump.

  • Accumulator.
  • The left hydraulic Accumulator is installed in the pump pressure line to absorbs shocks to the left system. The minimum nitrogen pressure to check on preflight is 1200 psi at 70°F / 21°C ± 25 psi per 10°F / 5°C difference. The gauge located in tail compartment (System 1).

  • Filter Manifold.
  • The filter Manifold in the tail compartment controls the direction of fluid travel. It contains 6 filters to provide filtered fluid and there are no pressure differential indicators to check.

  • Functions.
  • The left system powers the primary flight controls (elevators, ailerons, rudder) the midboard spoilers, as well as the left thrust reverser. The left system also performs a number of utility functions: Flaps, Gear, Brakes (Inboard), Nosewheel steering, Main Entrance Door.

  • Failure of Left System Pump Only
    • Results in loss of: Left Thrust Reverser, Midboard Spoiler Pair
    • Pilot Considerations
      • Airspeed 285 KCAS/.90M max
      • If Failure occurs ≤ 2 hours after takeoff: Land at nearest suitable field within 4 hours of failure, Flight control failure a concern due to viscosity issues related to possible high temp of EBHA trapped fluid
      • If failure occurs > 2 hours after takeoff: Land at nearest suitable field with no time limit, Hyd fluid temp stabilized → Flight control failure not a concern

Right System

[PAS, p. 8-4]

  • Independent.
  • The right system is independent and isolated from the left system.

  • Powered by.
  • Powered by the right Engine Driven Pump which is mounted on the engine gearbox. This pump outputs a constant pressure (3,025 ± 50 psi), variable volume. The volume is low at idle, higher at cruise. The pump offloads when in flight if an engine drops below idle (< 55% N2), (automatically controlled by Electronic Engine Controller). This reduces pump outlet pressure so as to reduces drag on the engine during an airstart. The system has a pressure relief valve to relieves pressure during surges at 3500-3750 psi.

  • Reservoir.
  • The right hydraulic Reservoir is smaller than the left and is considered full at 1.3 gal. It supplies hydraulic fluid for: Right Engine-Driven Pump.

  • Accumulator.
  • The right hydraulic Accumulator is installed in the pump pressure line to absorbs shocks to the left system. The minimum nitrogen pressure to check on preflight is 1200 psi at 70°F / 21°C ± 25 psi per 10°F / 5°C difference. The gauge located in tail compartment (System 2).

  • Functions.
  • The right system powers the primary flight controls (elevators, ailerons, rudder) the inboard and outboard spoilers, as well as the right thrust reverser. The right system also powers the outboard brakes and drive the PTU motor.

  • Failure of the right system results in the loss of the right thrust reverser. There are several pilot considerations:
    • Airspeed 285 KCAS/.90M max
    • If failure occurs ≤ 2 hours after takeoff: Land at nearest suitable field within 4 hours of failure (Flight control failure a concern due to viscosity issues related to possible high temp of EBHA trapped fluid)
    • If failure occurs > 2 hours after takeoff: Land at nearest suitable field with no time limit, if Hyd fluid temp stabilized → flight control failure not a concern

Power Transfer Unit (PTU)

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Photo: G500 Hydraulic System, PAS, p. 8-7

Click photo for a larger image

[PAS, p. 8-7]

  • Located on left side of tail compartment above Fluid Quantity Indicator
  • Primary backup for left utility systems when Left Engine-Driven Pump Inop
  • Gear, flaps, inboard brakes, nosewheel steering, main entrance door

  • Consists of a motor and pump assembly
  • Uses Right System pressure and Left System fluid. Motor is driven by right System Pressurized fluid, motor drives pump, pump pressurizes left system fluid to operate utilities.

  • When armed on OHPTS → DCN will trigger operation immediately when left system pressure < 2400 psi, fluid available in left and right system > 0.36 gal, right system pressure > 2850 psi, and right system fluid not hot < 107°C.
  • There is no time limit for operation. DCN will trigger deactivation 7 seconds after left system pressure recovers ≥ 2850 psi or immediately if right press drops < 2400 psi.

  • When manually selected ON
  • Minimum and maximum constraints when armed don’t apply, activates without time limit.

  • PTU shutoff valve
  • Located in PTU Motor Pressure Line, controlled by Armed and On switches on OHPTS → Hyd/CPCS, prevents right system from pressurizing PTU Motor when PTU motor not commanded to run.

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Photo: G500 Hydraulic System, OHPTS, PAS, p. 8-12

Click photo for a larger image

[PAS, p. 8-12]

  • Armed / Not Armed Switch
    • Downstate
    • Armed: Default position at power up, PTU Auto Operation is Armed and Triggered by DCN When left pressure < 2400 psi, left and right fluid available, left and right fluid not hot. DCN will trigger deactivation 7 seconds after left pressure recovers > 2850 psi or immediately if right pressure drops < 2400 psi.

      Armed: PTU has failed.

    • Upstate
    • Not Armed: PTU operation inhibited.

  • Off / On Switch
    • Downstate
    • On: PTU forced to operate.

    • Upstate
    • Off: Default position at power up, PTU shutoff valve closed

      On: PTU SOV Open (if activated by Armed Mode)

      Off: PTU SOV Closed and PTU Failed

      On: PTU SOV Open and PTU Failed( if activated by Armed Mode)

Aux Pump

If activated in flight, the Aux Pump automatically shuts down after 2 minutes.

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Photo: G500 Hydraulic System, Aux Pump, PAS, p. 8-6

Click photo for a larger image

[PAS, p. 8-6]

  • Logistics.
  • The aux pump is located in tail compartment below left hydraulic reservoir, it electrically powered by the Left Ess DC, and uses left system fluid.

  • Primary Function.
  • The aux pump provides hydraulic pressure for utility systems during ground / maintenance activities (gear, flaps, inboard brakes), nosewheel steering, and the main entrance door. The aux pump comes on automatically if the toe brakes are applied when the inboard accumulator is less than 1500 psi.

  • Secondary Function.
  • The aux pump provides an automatic backup to assist the PTU if necessary.

  • Auto Operation In Flight
  • Normally inactive, automatically provides power for flaps and gear after a dual engine failure, dual engine driven pump failure, or left engine pump and PTU failure.

    To activate: aux pump needs to be armed and not overloaded or overheated, left system pressure needs to be less than 1500 psi, the left system needs to be available ( > .36 gal and < 107°C), and the flap or gear positions do not match handle position when over 100 KCAS.

  • When Manually Selected ON
  • The minimum and maximum constraints when armed don’t apply. Activates Aux Pump on the ground without time limit, in-flight with a 2 min limit but it can reset by turning OFF then ON

  • Much slower operation of gear and flaps on Aux Pump alone due to a low flow rate
  • PTU → Approx. 23 gal / min, AUX → Approx. 2.5 gal / min

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Photo: G500 Hydraulic System, OHPTS, PAS, p. 8-16

Click photo for a larger image

[PAS, p. 8-16]

  • Armed / Not Armed Switch
    • Downstate
    • Armed: Default position at power up, Aux pump auto operation is armed and triggered by DCN when left pressure < 1500 psi, left fluid available, left fluid not hot, and flap or gear handle doesn't equal actual positions.

      Armed: Aux pump has failed.

    • Upstate
    • Not Armed: Aux pump auto operation inhibited.

  • Off / On Switch
    • Downstate
    • On: Aux pump forced to operate.

    • Upstate
    • Off: Default position at power up, Aux pump off.

      On: Aux pump on (if activated by Armed Mode).

      Off: Aux pump off and failed.

      On: Aux pump forced to operate.


The components in greater detail . . .


Accumulators

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Photo: G500 Hydraulic System, , PAS, p. 8-4

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[FSI G500 MTM, p. 38]

  • There are two 50 cubic-inch hydraulic accumulators, one for each engine driven system, located on either side of the tail compartment. They are installed in the hydraulic pressure lines downstream of the filter manifold. Their purpose is to act as hydraulic shock absorbers and dampen hydraulic pressure surges within the system caused by the rapid loading and unloading of the various system components. They are also used to supply initial quick flow demands until the EDP can react to meet a rapid increase in system demand. The accumulators are serviced with a precharge of 1200 psig of nitrogen (at 70°F) via a combination service valve and pressure gage located on the accumulator servicing panel in the tail compartment. The nitrogen precharge ensures proper operation of the accumulator.

Engine Driven Pumps

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Photo: G500 Hydraulic System, Pump, PAS, p. 8-2

Click photo for a larger image

[FSI G500 MTM, pp. 29 - 30]

  • An engine-driven hydraulic pump (EDP) is mounted on the aft face of each engine accessory gearbox. The variable volume and displacement, pressure compensated pumps can vary their outlet flow, based on system demand, to maintain a constant system pressure of 3000 psi. The pumps rotate any time the HP compressor of the engine is turning.

  • With the engine operating, fluid is directed from the reservoir through the motor operated shutoff valve to the EDP suction port. A portion of the incoming fluid is used internally for pump cooling and lubrication. This hot bypass fluid exits the pump via the Case Drain port and is routed to heat exchangers in the fuel tanks. Pump outlet pressure is maintained at 3000 psi throughout the aircraft pressure lines and is available for use by hydraulic user components.

  • The G500/G600 operates a hydraulic offload (depress) function, which when energized, minimizes the pressure and flow from the EDP and effectively unloads the pump from the gearbox. This function is designed to assist with engine windmill starting performance following an in-flight engine shut down. The pump remains connected to the gearbox and continues to rotate, however hydraulic pressure and flow from the pump is minimal which reduces the torque needed to turn the pump. Hydraulic offload is controlled by the associated Electronic Engine Controller (EEC) via a depressurization solenoid valve mounted to each pump. Power to the solenoids is provided from the on-side Essential DC Bus via MPTs 6 and 12.

  • The EDP will be offloaded (Depressurization Solenoid energized) if engine HP RPM drops below idle with the aircraft in-flight. The affected pump remains off-loaded until successful completion of an in-flight start or the aircraft lands.

Filter Manifolds

Sometimes you have to wonder, "what am I supposed to do with this knowledge?" These manifolds were a preflight item on previous Gulfstreams because there were a total of 10 Differential Pressure Indicators to check. Those DPIs are gone and these manifolds are more a maintenance concern that one for us pilots to check.

[PAS, p. 8-9]

  • Left, Right, Aux
  • Located in tail compartment
  • Controls direction of fluid travel
  • Contains filters to provide components with filtered fluid
  • Some by-passable, some not; disposable micron filters; replaced at scheduled intervals; no pressure differential indicators to check; Left System Manifold → 6 filters, Right System Manifold → 3 filters, Aux System Manifold → 1 filter

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Photo: G500 Hydraulic System, Right System Manifold, PAS, p. 8-9

Click photo for a larger image

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Photo: G500 Hydraulic System, Left System Manifold, PAS, p. 8-9

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Photo: G500 Hydraulic System, Aux System Manifold, PAS, p. 8-9

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Heat Exchangers

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Photo: G500 Hydraulic System, Heat Exchangers, PAS, p. 8-10

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[PAS, p. 8-10]

Radiator-type heat exchangers submerged in corresponding fuel hopper used to cool hydraulic fluid while warming hopper fuel. It is always circulating with no pilot controls.

[FSI G500 MTM, p. 33]

  • The engine driven hydraulic pumps rotate anytime the engines are running. When there is no demand on the hydraulic system, system pressure stabilizes at 3000 psi but there is very little flow of fluid. A quick overheat would occur if there were no transfer of fluid through the pump when there is no demand on the system. To cool and lubricate the EDP, some hydraulic fluid from the suction (inlet) port is allowed to bypass into the pump housing. This fluid removes heat and may contain contamination from pump wear and is removed from the pump via the case drain (bypass) port.

  • The purpose of the heat exchanger is to cool the case drain fluid heated by the pumps by transferring the heat to the fuel in the hopper. The heat exchanger is a radiator type heat exchanger installed close to the floor of the hopper section of the wing fuel tanks. During cold weather start-up, cold case drain fluid coming from the pumps will have a higher than normal viscosity and will bypass the heat exchanger through a bypass valve located in each filter manifold. When the case drain fluid warms and the pressure drops, the bypass valve will close directing the warm fluid to the heat exchanger.

Hydraulic Shutoff Valves

Work in progress

Pressure Relief/Unloading Valves

Work in progress

Pressure Transducers

Work in progress

Quantity Measurement

Digital

Work in progress

Visual

Work in progress

Temperature Compensation

Work in progress

Quantity Compensation

Work in progress

Reservoir Assemblies

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Photo: G500 Hydraulic System, Reservoirs, PAS, p. 8-2

Click photo for a larger image

[FSI G500 MTM, p. 15]

  • The hydraulic reservoirs are located in the tail compartment, at approximately the 10:00 (left) and 2:00 (right) o’clock positions. The purpose of the hydraulic reservoir assembly is to store hydraulic fluid under pressure and to remove entrained air from the fluid. Each bootstrap type reservoir is hydraulically pressurized from its respective system pressure. This is accomplished by a pressure operated piston within the reservoir.

  • When the small end of a piston within the bootstrap cylinder is actuated by pressurized fluid from the EDP, the fluid supply within the reservoir is pressurized by the large end of the piston. When bootstrap pressure is 3000 psi, the reservoir fluid is pressurized to approximately 60 psi. This provides the pumps with pressurized fluid for operation.

  • Each reservoir assembly incorporates a pressure relief valve, a manual bleed valve, fluid quantity transmitter and a visual quantity indicator. A standpipe is attached to the top of each reservoir to collect any air that may be introduced into the fluid during system operation.

  • The air collects around the top of the reservoir and migrates upward into the standpipe. The reservoirs are mounted in the aircraft with a 5° aft tilt to assist with air collection in the standpipe. This allows for the air to be captured and bled, precluding high concentrations of air from entering the EDPs.

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Photo: G500 Hydraulic System, Right system reservoirs cutaway, PAS, p. 8-8

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[PAS, p. 8-8]

  • Bootstrap Chamber (Yellow)
  • High pressure chamber (3000 psi), compresses one of walls of system chamber to maintain 60 psi inside the system chamber. (“Bootstrap” means system is self-pressurizing).

  • System Chamber (White)
  • Considered full: Left → 2.5 gal, Right → 1.3 gal

    Considered low (no dispatch): Left < 1.75 gal, Right < 0.81 gal. Note: Dispatch decisions should be based on presence of L-R Hyd Quantity Low CAS message.

    Fluid quantity is derived from the movement of a Rotary Variable Differential Transformer (RVDT) connected to a large internal piston within the reservoir. The reservoir must be pressurized to indicate accurately. Can be read electronically on synoptic pages or at a sight gauge on the high pressure end of the reservoir.

    An RVDT is defined as a Rotary Variable Differential Transducer through most of this manual.

  • Hydraulic Firewall Shutoff Valves
  • Located between each reservoir and Engine-Driven Pump. Stops flow of fluid in event of engine fire. Protects remaining fluid in reservoir if hyd line ruptures around engine. Electrically controlled by Left and Right Fire Handle (L / R Essential DC). When pulled → closes valve.

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Photo: G500 Hydraulic System, TSC, PAS, p. 8-20

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[PAS, p. 8-20] Quantities are available on TSC #1, #2, #3, and #4 ground service pages or TSC #5 fluid quantity page. Note: Quantities on TSCs may differ from synoptic page by 0.2 gallons.

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Photo: G500 Hydraulic System, 1/6th Synoptic, PAS, p. 8-25

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[PAS, p. 8-25] Hydraulic Remote Replenishing System

  • Located on right side of tail compartment at top of ladder, used to add hyd fluid to reservoir when needed.
  • Exterior Preflight Inspection (Expanded): replenishing Selector Valve → OFF to avoid transmission of fluid in flight, Hydraulic Replenisher → Verify fluid level cap secure, Hydraulic Accumulators → 1200 psi.
  • Separate replenishment pump (oil has its own pump too).
  • Replenishing considered a maintenance function; aircrew can perform if properly trained; see OM Handling and Servicing Procedures → Pilot Hydraulic Fluid Servicing Procedure.

[PAS, p. 8-25] Fluid Quantity Indicator (FQI)

  • Located on left side of tail compartment at top of ladder on the oil replenishment panel.
  • Dual purpose as hydraulic and oil quantity indicator; Hydraulic quantities shown on left for Left and Right Systems; SELECT switch (bottom left) used to change left or right digital indication; displays digital quantity; also displays “LO”, “OK”, or “HI”; Activates replenishing pump; HYD or OIL switch (bottom center) used to select which quantity indications to view; OFF / ON or TEST switch (bottom right) turns FQI display only ON and OFF; FQI still functional; initiates test of the FQI Display.

Limitations and Abnormal Procedures


Limitations

[G500 AFM, §01-29-10] Hydraulic Servicing

  • Maximum reservoir quantities (pressurized) as indicated on the Hydraulics synoptic page: Left Hydraulic System → 4.6 gallons, Right Hydraulic System → 2.8 gallons.
  • Left and Right Hydraulic System Accumulator pre-charge: 1,200 psi at 70°F / 21°C, ± 25 psi for each 10°F / 5°C difference in temperature from 70°F / 21°C.

[G500 AFM, §01-29-20] Flight Time Limitation after Hydraulic Failure

  • Land within 4 hours of a hydraulic system failure if the failure occurred within 2 hours of takeoff.
  • Note: If a hydraulic system failure occurs > 2 hrs after takeoff, the hydraulic fluid temperature has stabilized and there are no flight time restrictions.

References

Gulfstream GVII-G500 Airplane Flight Manual, Revision 1, August 31, 2018

Gulfstream GVII-G500 Production Aircraft Systems, Revision 1, Oct 1, 2018

Revision: 20190528
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