Utility System Flashcards
Utility Reservoir/Cooler Assembly
Cooler
(a) The cooler is mounted on top of the reservoir.
(b) Hydraulic fluid cools in the cooler prior to returning to the reservoir.
(c) The fluid is cooled by drawing air through the cooler assembly using an electric fan.
Cooler Fan
(a) The utility reservoir cooler fan is located in the upper portion of the aft pylon.
(b) The fan is connected to the cooler assembly by flexible ducting.
(c) The temperature switch, located on the reservoir, controls the fan operation.
(d) Electrical power required to operate the fan is supplied by an Alternating Current (AC) and Direct Current (DC) source located on the No. 1 Power Distribution Panel (PDP).
(e) The UTIL HYD COOLING BLOWER circuit breaker, located on the No. 1 AC bus, operates the fan.
(f) If either the No. 1 AC or No. 1 DC system fails with no bus-tie, the hydraulic oil cooler fan will not function.
Reservoir
(b) The reservoir stores cool hydraulic fluid for the utility hydraulic system under 60 PSI.
(c) When the utility or APU motor pumps are not operating the utility reservoir pressurization accumulator exerts the required head pressure to maintain 60 PSI on the fluid supply in the reservoir.
(d) When the pumps are operating, system pressure of 3000 PSI maintains the fluid supply pressure.
(e) The capacity of the reservoir is 5.6 quarts or 5.3 liters of hydraulic fluid.
Visual Fluid Level Indicator
(a) The visual fluid level indicator is a mechanical means of determining the actual fluid level in the reservoir providing an accurate fluid level indication.
(b) With the ramp in the full down position the fluid level indicator will show a portion of the green band.
(c) When the ramp is in the full up position the fluid level indicator will extend past the green band.
Temperature Bulb
The temperature bulb, located on the supply port on reservoir, electrically transmits the fluid temperature to the indicator on the maintenance panel.
Cooler Bypass Valve
(a) The cooler bypass valve is located between the return and supply ports on the reservoir.
(b) When return pressure to the cooler exceeds supply pressure to the pump, the fluid bypasses the cooler.
(c) This occurs if the cooler becomes clogged or the fluid is thick (high viscosity) which will take increased amount of pressure to push the fluid through the cooler during cold weather.
Linear Variable Differential Transducer (LVDT)
(a) The LVDT is located in the center of the reservoir inside the visual level indicator.
(b) The LVDT indicates the level of fluid inside the reservoir based on the position of the floating piston that divides the fluid from the ambient air.
LVDT Electrical Connector
(c) An electrical connector on the aft end of the reservoir transmits the fluid level reading to the indicator on the maintenance panel.
Bleed Relief Valve
(a) The bleed relief valve is located at the top of the reservoir where air collects from the self bleeding feature of the system, just above the LVDT electrical connector.
(b) The valve provides two purposes.
(c) The first is to manually bleed air from the reservoir.
(d) The second is protection of the reservoir against over-pressurization. (e) The valve begins to open when pressure reaches 100 PSI and is fully open when the pressure reaches 125 PSI.
(f) The fluid drains through the HYDR COMPT DRAIN tube on the No. 2 side of the ramp area.
Utility Reservoir Pressurization Accumulator
(1) The utility reservoir pressurization accumulator maintains a return pressure of 60 PSI on the supply fluid in the utility reservoir cooler assembly.
(2) During APU motor pump starting, the accumulator prevents pump cavitations by supplying a continuous flow of fluid.
(3) Pressure from the accumulator is applied to the back side of the utility reservoir cooler assembly piston at approximately 3000 PSI, the accumulator pressure pushes on the fluid which has an area that is 50 times larger resulting in supply fluid pressure of 60 PSI.
(4) When performing a preflight inspection, verify that the accumulator gauge reading is between 2500–3500 PSI.
Utility Reservoir Pressurization Accumulator
Utility Reservoir Depressurization Valve
(1) The utility depressurization valve is located on the right side of the ramp area at STA 555.
(2) When the valve is in the OPEN position it allows the utility reservoir pressurization accumulator to be depressurized when the APU start module depressurization valve is pressed.
Electric Pump for the Utility System Hydraulic Accumulator (EPUSHA)
(1) In addition to the hand pump, an EPUSHA is installed.
(2) The EPUSHA system consists of an electric hydraulic pump and pump control box located in the aft cabin used to provide a less labor intensive means of pressurizing the APU start accumulator to start the APU.
(3) The electric hydraulic pump is a fixed displacement, radial piston, electric motor driven pump that operates on 18–30 Volts Direct Current (VDC) supplied by the aircraft battery.
(4) The system is equipped with an over pressurization switch that shuts off the pump at 3150 PSI ±150.
(5) The EPUSHA is controlled by a pump control box located in the aft cabin area.
(6) The control box has a three position switch that is spring loaded to the center (NEUTRAL) position.
(7) A momentary toggle to the START position begins pump operation, and a momentary toggle to the STOP position will stop pump operation.
(8) If the aircraft battery voltage drops below 20 VDC, the voltage sensing relay shuts down the pump.
(9) If the pump shuts down, the hand pump must be used to reach the desired pressure.
(10) Power to operate the EPUSHA is supplied by the battery bus through the ACC PUMP circuit breaker located on the No. 1 PDP.
g. APU Start Accumulator
(1) The APU start accumulator is mounted overhead in the cabin on the right hand side of the aft transmission sump compartment.
(2) The accumulator is used to store hydraulic fluid under pressure to start the APU.
(3) In an emergency, the pressure in the accumulator can be used to operate the utility hydraulic subsystems.
(4) The APU start accumulator, a self-displacing type accumulator, is divided into four sections:
(a) Section 1 holds the air or nitrogen gas pre-charge which is used to force the pressurized fluid to the utility system or the APU motor pump.
(b) Section 2 holds pressurized hydraulic fluid.
(c) Section 3 holds return fluid. (d) Section 4 allows atmosphere pressure to vent.
APU Start Accumulator Diagram
(5) The APU start accumulator with a pressure gauge and charge valve mounted on the end of the APU start accumulator located outboard of the aft transmission sump compartment.
(6) The precharge is In Accordance With (IAW) the checklist, usually between 1800–2100 PSI.
(7) When conducting a preflight inspection, ensure the pressure indicated is 3000 PSI.
Emergency Utility Pressure Valve
(1) The emergency utility pressure valve is located at STA 530 above the EPUSHA.
(2) When the valve is in the OPEN position, it allows the APU start accumulator, or hand pump (in some emergencies) to pressurize the utility system.
(3) During power OFF operations, pressure from the valve can be used for the winch, brakes, and ramp subsystems.
APU Start Module
(1) The APU start module is located in the ramp area, aft of the APU start accumulator.
(2) The APU start module is comprised of five components: accumulator pressure gauge, APU start module accumulator, APU start module depressurization valve, APU start module start solenoid valve, and the pressure operated APU start valve.
(3) The accumulator pressure gauge indicates the pressure in the APU start accumulator.
(4) When properly charged, this gauge should indicate approximately 3000 PSI.
(5) After the APU is commanded to start, hydraulic pressure is released from the APU start accumulator through the APU start module to the APU motor pump.
(6) When the APU reaches 90% N1 the start module signals the APU motor pump to shift from start motor mode to pump mode.
(7) When pressed the depressurization valve depressurizes the following: (a) Utility system and subsystems
(b) APU start module accumulator
(c) APU start accumulator
(d) Reservoir pressurization accumulator, (as long as the utility reservoir depressurization valve is open).
(8) This valve is normally used to perform maintenance on the utility system or to check pre-charges.
(9) The APU start solenoid valve is activated by the Electronic Sequencing Unit (ESU) when the APU start switch is placed in the start position.
(10) The solenoid valve is controlled by the ESU during the APU start to remove fluid pressure from the APU motor pump when the APU reaches 90% N1.
(11) The pressure operated APU start valve is a slow opening mechanical valve that prevents shearing of the shaft between the APU motor pump and the APU reduction drive.
Utility Hydraulic Pump
(1) The utility hydraulic pump, located on the No. 2 side of the aft transmission, provides constant output pressure of 3000 PSI to the system with a flow rate of 16.5 Gallons Per Minute (GPM) when the rotors are turning at 100% Rotor Revolutions Per Minute (RRPM).
(2) The hydraulic fluid flow is provided by drawing in fluid from the supply port into the pistons.
(3) The piston stroke is adjusted by the positioning of the swashplate which varies the amount of fluid drawn in and pressurized.
(4) The swashplate is adjusted by an internal piston inside the pump which holds the swashplate in a neutral position when there is no demand on the pump.
(5) As demand is placed on the pump, the pressure to the internal piston is reduced allowing the swashplate to increase the pitch and increase the flow.
(6) Additionally, the pump is lubricated and cooled by hydraulic fluid.
(7) The pump has four ports; supply, pressure, case drain, and the seal drain.
(8) The case drain port carries the hydraulic fluid that passes between the pistons inside the pump and the piston housing.
(9) The rate of flow exceeds 2.5 GPM ±.25 GPM, the pump fault light on the maintenance panel will illuminate.
(10) The supply port supplies hydraulic fluid to the pump at 60 PSI.
(11) The pressure port supplies hydraulic fluid to the system at 3000 PSI. (12) The seal drain port allows hydraulic fluid or oil leakage between the pump and the aft transmission to drain from the system.
APU Motor Pump
(1) The APU motor pump is located on the forward end of the APU at STA 594
(2) The pump portion provides 3350 PSI of hydraulic pressure to start the main engines, complete ground checks or maintenance.
(3) The APU motor pump can also be used in an emergency, should the transmission driven utility pump fail during flight.
(4) During APU start 3000 PSI from the APU start accumulator is sent to the APU shuttle valve through the signal line changing the position of the valve.
(5) As the signal fluid is sent, the pressure operated valve in the APU start module opens slowly to allow 3000 PSI from the start accumulator to go to the APU motor pump.
(6) The fluid flows to the wobble plate through the shuttle valve changing the motor/pump into the motor mode; simultaneously the pressurized fluid begins to turn the motor.
(7) At approximately 20% of the Gas Producer Speed (N1) the charge in the APU start accumulator is depleted, the APU motor pump is no longer driving the APU, allowing the APU motor pump to return to the neutral mode.
(8) While in the neutral mode, the APU motor pump continues to maintain constant pressure to the APU motor until approximately 90% N1.
(9) At about 90% N1 the ESU removes power from the APU start module solenoid valve closing it, shifting the APU motor pump to the pump mode producing 3350 PSI.
(10) The APU motor pump re-pressurizes the APU start accumulator.
Pressure Control Module
(1) The pressure control module receives input hydraulic pressure from the APU motor pump, utility pump, or an external ground power unit (AGPU) and distributes it to the various utility hydraulic subsystems.
(a) Engine Start Solenoid Valves
Engine Start Solenoid Valves
1) Located on the pressure control module are the No. 1 and No. 2 engine start solenoid valves.
(2) The engine start solenoid vales are normally closed, but are electrically opened when the ENG START switch on the overhead FADEC panel is placed in either the 1 or 2 position.
(3) 28 VDC is supplied from each respective essential bus.
(4) The start solenoid valves work with the engine Pressure Operated Valve (POV) to control the flow of fluid to the engine starters.
(5) The start solenoid valves allow hydraulic fluid to pass to the appropriate engine POV.
Engine Pressure Operated Valves
1) The No. 1 and No. 2 engine POVs are normally closed and hydraulically opened valves.
(2) The valves are spring loaded to the closed position, opening by hydraulic fluid pressure controlled by each respective pilot solenoid valve.
(3) The engine POVs are slow opening valves which allow fluid pressure to build slowly to prevent damage to the respective engine starter.
PTU, Hook, and Winch Solenoid Valve
(1) The PTU, Hook, and Winch solenoid valve works with the PTU, Hook, and Winch POV to control the flow of hydraulic fluid to the PTUs, winch, and center cargo hook at the pressure control module when energized.
(2) The solenoid valve is electrically energized open as soon as the No. 1 DC bus comes on line, which closes the POV and removes pressure from the four systems (No. 1 PTU, No. 2 PTU, Cargo Hook, and Hoist/Winch).
(3) The solenoid valve is normally closed when any of the following occur:
(a) Loss of the No. 1 DC power occurs with a bus tie b) Power is removed from the No. 1 DC bus c) Aircraft is shutdown
(4) The solenoid valve is de-energized closed when one or more of the following four switches are toggled:
(a) No. 1 PWR XFER switch to the ON position
(b) No. 2 PWR XFER switch to the ON position
(c) Cargo hook switch to the ARM position Hoist/Winch switch to the PLT or REMOTE position
(5) The solenoid valve is de-energized closed in this case since the solenoid valve is currently held open by using power from the No. 1 DC bus.
(6) Electrical power is being removed from the solenoid using the switch.
(7) When the power is removed hydraulic pressure opens the POV allowing hydraulic fluid to pass to the four systems.
(8) To isolate one or more of the PTUs, Winch, or Cargo Hook systems, all four switches must be placed in the OFF position.
PTU, Hook, and Winch Pressure Operated Valve
(1) The PTU, Hook, and Winch POV is spring loaded to the normally open position and hydraulically closed.
(2) The valve is controlled by the PTU, Hook, and Winch solenoid valve.
Power Steering, Swivel Locks, and Brake Solenoid
(1) The power steering, swivel locks and brake solenoid isolates the power steering, swivel lock, and brake systems in the event of a leak in the system, by activating the PWR STEER switch on the hydraulic panel located on the overhead console.
(2) The solenoid is normally open, electrically closed, and controlled by 28 VDC.
Pressure Transmitter
(1) The pressure transmitter converts fluid pressure into an electrical signal. (2) The electrical signal (pressure indication) is transmitted to the hydraulics utility pressure indicator on the maintenance panel.
(3) The normal pressure range is 2500–3500 PSI.
Pressure Switch
(1) The pressure switch controls the UTIL HYD PRESS LO caution light on the Multifunction Display (MFD).
(2) Whenever hydraulic pressure drops below 1800 PSI in the utility hydraulic system the caution will illuminate.
(3) The caution extinguishes as increasing pressure approaches 2300 PSI. (4) Normally, the caution illuminates at 2000 PSI. 5) NOTE: The pressure switch is not linked to the maintenance panel hydraulic pressure indicator.
High Pressure relief Valve
(1) The high pressure relief valve prevents over-pressurization of the pressure control module in the event of a high-pressure state.
(2) The valve is spring loaded in the closed position.
(3) As pressure reaches 3500 PSI the valve begins to open and is fully open at 3850 PSI.
(4) When the pressure is reduced the valve will begin to close at 3500 PSI. (5) The relieved fluid is sent to the return module where it is filtered and sent back to the reservoir.
Pressure Filter Assembly
(1) The filter bowl assembly is separated into three areas
(a) Filter Bowl 1 The filter bowl contains a 5 micron disposable type filter. 2 This filter is the same type that is used throughout the aircraft hydraulic system.
(b) Visual Contamination Indicator
1 The visual contamination indicator is a button that extends when a differential pressure of 75 PSI ±10 exists between the inside and outside of the filter element.
2 If the indicator button is extended complete the following:
a Reset the button
b Motor the engine for 30 seconds
c If button extends again during motoring replace filter
d Filter does not have a bypass capability
(c) Filter Change Transmitter The filter change transmitter contains a micro switch that when activated by the visual contamination indicator illuminates the FLTR CHNG PRESS light on the maintenance panel.
Return Control Module
(1) The return control module is the central location for the return components, which includes the return filter, an APU motor pump fault indicator, a utility hydraulic pump fault indicator, and various check valves. (2) The main purpose of the return control module is to provide a source of return while providing subsystem isolation to prevent loss of the entire system if one return line breaks.
(3) The filter bowl assembly is separated into three areas:
Pump Fault Indicators
(a) Located on the return control module are two pump fault indicating buttons, one for the APU motor pump and one for the utility hydraulic pump.
(b) As the flow rate from the pump drain exceeds 2.5 GPM across the button, which is connected to a sensor, the corresponding light (APU PUMP FAIL or UTIL PUMP FAIL) will illuminate.
(c) A high flow rate from the case drain of a pump may indicate an impending pump failure.
Engine Starter
(1) The engine starter is located at the 12 o’clock position on either engine. (2) The engine starter is a hydraulic motor used to drive the engine compressor.
(3) When the ENG START switch on the FADEC panel is set to the 1 or 2 position the associated pilot solenoid valve is energized, allowing hydraulic pressure to flow through the associated POV to the engine starter
