Utility Hydraulic Flashcards
General
System has several ways for hydraulic power to be supplied to subsystems, mainly through the utility hydraulic pump being driven by the AGB when rotors are turning. During ground operations with rotors stopped/engines not running, an APU motor/pump can be used to drive the AGB, which will power the utility hydraulic pump and therefore the utility hydraulic subsystems
Those systems are:
- Cargo hook
- APU start system
- Main engine start system
- Wheel brakes
- Swivel lock
- Power steering
- Ramp
- Hoist (when installed)
EPUSHA
Installed on right side of ramp below manual hand pump, is used to pressurize the 200 cu inch accumulator or fill utility hydraulic reservoir
It is a fixed displacement hydraulic pump rated at 0.71 gym, attached to an explosion proof DC electric motor with a reduction gearbox, has filter assemblies, an electric relay, and control panel
To pressurize 200 cu inch accumulator:
- Turn aircraft battery ON
- Set manual control valve to NORMAL
- Move arming switch on control panel to ARMED
- Hold spring loaded ON/OFF switch to ON until reaching desired pressure (max 3000psi)
To refill utility hydraulic reservoir:
- Turn aircraft battery ON
- Set manual control valve to FILL
- Fill filler tank with fluid
- Move arming switch to ARMED
- Hold spring loaded ON/OFF switch to ON until reservoir is filled
Power is provided by No. 1 28vdc emergency bus through CB on No. 1 PDP labeled AUX UTILITY PUMP
200 Cu. In. Accumulator
Stainless steel sealed tubular assembly complete with internal floating separator piston
It is pre charged with nitrogen or dry air to a preload pressure of 1400 psi
Functions is to store pressurized fluid for APU starting and can supply pressure for the limited operation of utility subsystems
Also provides backup pressure when large demands are made on system
Utility Reservoir
Stainless steel tube sealed with quantity indicating dipstick
To provide positive supply to utility pump, reservoir is pressurized whenever utility system is pressurized. This is accomplished by taking pressurized fluid from 25 cu in accumulator and passes this pressurized fluid tor rear face of internal separator piston within reservoir.
Position of separator piston will always be dictated by quantity of fluid within reservoir. Attached to piston is dipstick, which is marked FULL or REFILL.
Utility Hydraulic Pump
Mounted to aft end of AGB and supplies pressure fluid to all utility hydraulic systems
Constant pressure type that is self adjusting to produce 3350psi
25 cu. in. Accumulator
Smol version of 200 cu in accumulator, provides a constant pressure for “Boot Strap” pressurization of utility system reservoir. Pre load air or nitrogen is 1400psi
Utility System Isolation Valve
Solenoid valve used to retain pressure within 200 cu in accumulator when rotors and APU shut down
Automatically closes when APU or main engines are started to remove all utility pressure from subsystems to allow max pump output for start sequence
APU must not be started during ground taxiing because all braking and steering will cease to function
Utility Hydraulic System Switch
On overhead panel marked UTIL-ON/OFF
With switch ON, DC emergency bus supplies power to open normally closed solenoid valve. This directs 200 cu in accumulator pressure to utility subsystems, and permits limited use of of hydraulic equipment on ground without external hydraulic power or APU running
With switch OFF, solenoid valve closes
Cooler Unit
Found on RH ramp area, unit is positioned between return manifold and return filter in utility system return line
Cooler has a duct, hydraulic motor fan, and cooler
Pressurized fluid flows from utility system valve through motor to operate fan and then flows into return line. Hot hydraulic fluid flows through cooler and is cooled by air drawn in by the fan
Fan Control Valve
Valve operates with thermostatic switch to allow pressurized fluid to enter IN port of cooler fan motor
Switch closes when hydraulic fluid temperature reaches 68* C
Fluid Cooler Thermostatic Switch
Unit is threaded into low pressure manifold next to hydraulic fluid cooler
When temp is high, the switch contacts close to energize the fan control valve and operates the fan
When fluid temp decreases, switch contacts open to de energize fan control valve and stops the fan
Contacts close 65.5 to 71.1*C
Contacts open 61.1 to 65.5*C
Utility Hydraulic Cooler Test Switch
Located on RH side of aft fuselage
Has 2 positions, TEST and spring loaded OFF
With switch at test the cooler fan solenoid valve energizes and provides utility hydraulic pressure to cooler hydraulic motor driving the cooler fan. During TEST, cooler fan solenoid thermal switch is bypassed allowing checkout of system
Utility Hydraulic Overtemperature Switch
Switch closes when fluid temp reaches 134.4 to 141.1*C, which illuminates UTIL HOT on overhead panel and HYD OVERTEMP caution light on annunciator panel
When temp falls below 116 to 125.5*C, the switch opens
Utility Hydraulic Pressure Indicating System
Consists of pressure transmitter, indicator gauge, and wiring
System powered by 26v AC supplied by No. 2 instrument bus
Normal operating range (green arc) is 2700 to 3500 psi
Main Engine Start System
Hydraulic starters are motored by 4000psi from utility hydraulic pump
During engine start, utility pump output increases from 3000psi to 4000psi to provide pressure to drive starters and all other subsystems are isolated
After engine start, and start switch placed OFF, pump output pressure returns to 3000psi and isolation valve opens