MH-60R - Systems - Hydraulic Flashcards
(28 cards)
What are the hydraulic system components?
Three identical and interchangeable hydraulic pumps, two transfer modules, one utility module, three dual-stage primary servos, tail rotor servos, the pilot-assist servo assembly, the APU accumulator, and the rescue hoist.
What does the hydraulic system do?
Three hydraulic pumps provide hydraulic pressure to hydraulic components of the flight control system, the APU system, and the rescue hoist system.
What pressure do all hydraulic system components receive, other than the pitch and roll trim actuators?
3,000 psi
When does the HYD warning light illuminate?
As a result of several compound malfunctions involving the No. 1, No. 2, and backup hydraulic systems.
What does the No. 1 hydraulic system power to?
First stage of the primary servos and the tail rotor servo.
What are the components of the No. 1 hydraulic system?
- No. 1 hydraulic pump
- No. 1 transfer module
- first stage of the primary servos
- first stage of the tail rotor servo
Describe the No. 1 hydraulic pump module.
The No. 1 hydraulic pump is a combination hydraulic pump/reservoir mounted on, and driven by, the left accessory module. The pump incorporates a pressure relief valve, bleed valve, pressure filter, return filter, and an automatic low-level sensing switch. The reservoir has a level-indicator window marked with red, green, and blue indicators that correspond to underserviced, normal, and overserviced hydraulic fluid levels, respectively. The pressure relief and bleed valves protect the pumps from high pressure in the return system. The pressure and return filters each contain a red PDI that extends when a pressure differential above the prescribed limit exists. The pressure filter has no bypass valve to preclude unfiltered fluid from entering the primary servos. The return filter bypass valve opens when return pressure reaches the prescribed pressure limit. The automatic low-level sensing switch, mounted on top of the pump, closes when fluid level is low, causing the #1 RSVR LOW caution to appear
Describe the No. 1 transfer module.
The No. 1 transfer module routes hydraulic fluid from the No. 1 hydraulic pump to the first stage of the primary servos and the first stage of the tail rotor servo. The No. 1 transfer module automatically routes hydraulic fluid from the backup pump if No. 1 hydraulic system pressure is lost. The components of the No. 1 transfer module include a transfer/shuttle valve, pressure switch, first-stage primary servo shutoff valve, and first-stage tail rotor servo shutoff valve. If No. 1 hydraulic system pressure is lost, the transfer/shuttle valve routes backup pump hydraulic fluid to the first stage of the primary servos and the first stage of the tail rotor servo. The pressure switch illuminates the #1 HYD PUMP caution and sends a signal to the LDI when No. 1 hydraulic pump pressure drops below prescribed limits. The first-stage primary servo shutoff valve is actuated using the pilot or copilot SERVO switch securing hydraulic pressure to the first stage of the primary servos. The first-stage tail rotor servo shutoff valve is actuated by the TAIL SERVO switch securing hydraulic pressure to the first stage of the tail rotor servo
What does the No. 2 hydraulic system supply power to?
The second stage of the primary servos and the pilot-assist servo assembly.
What are the components of the No. 2 hydraulic system?
- No. 2 hydraulic pump
- No. 2 transfer module
- second-stage primary servos
- pilot assist servo assembly
Describe the No. 2 hydraulic pump module.
The No. 2 hydraulic pump components and functions are identical to the No. 1 hydraulic pump except that the No. 2 hydraulic pump is mounted on, and driven by, the right accessory module. The automatic low-level sensing switch mounted on top of the pump closes when fluid level is low, causing the #2 RSVR LOW caution to appear.
Describe the No. 2 transfer module.
The No. 2 transfer module routes hydraulic fluid from the No. 2 hydraulic pump to the second stage of the primary servos and the pilot-assist servo assembly. The No. 2 transfer module is identical to the No. 1 transfer module except that it incorporates the second-stage primary servo shutoff valve. The second-stage primary servo shutoff valve is actuated using the pilot or copilot SERVO switch securing hydraulic pressure to the second stage of the primary servos. The pilot-assist servo shutoff valve is actuated by the LDI system securing hydraulic pressure to the pilot-assist servo assembly. Hydraulic pressure (approximately 1,000 psi) to the pitch and roll trim actuators can be secured by depressing the TRIM pushbutton on the AFCS CONTROL panel. Hydraulic pressure (approximately 3,000 psi) to the boost servos (collective, pitch, yaw) and Stability Augmentation System (SAS) actuators can be secured by depressing the SAS/BOOST pushbutton on the AFCS CONTROL panel.
Describe the primary servo shutoff
Two SERVO switches (one on each collective) secure hydraulic pressure to an improperly operating primary servo stage. When either 1ST OFF or 2ND OFF is selected, the associated servo shutoff valve is energized closed and hydraulic pressure to the respective stage is secured. When at least one of the three pressure switches on the first or second stage of the primary servos senses low hydraulic pressure, a circuit is completed that actuates the #1 or #2 PRI SERVO PRESS caution. The switch is normally placed in the unmarked center (ON) position. An electrical interlock prevents the securing of hydraulic pressure to both first and second stages simultaneously. In the event of a malfunctioning stage, it also precludes the inadvertent securing of hydraulic pressure to the operable stage.
Describe the Backup hydraulic system.
The backup hydraulic system supplies hydraulic pressure to the No. 1 and No. 2 hydraulic systems prior to rotor engagement, provides hydraulic pressure to the rescue hoist system, and recharges the APU accumulator. It also supplies emergency hydraulic pressure to the No. 1 hydraulic system, the No. 2 hydraulic system, and the second stage of the tail rotor servo when pressure loss occurs. When the backup pump is supplying pressure to the #2 tail rotor servo, the priority valve may secure hydraulic pressure to the rescue hoist due to low system pressure. System components include the backup hydraulic pump and the utility module.
What are the 2 cautions and 1 note associated wi the backup pump?
CAUTION:
If the BACKUP PUMP PWR circuit breaker is out and a condition exists that requires the backup pump to operate, then either the hydraulic system must be configured so that the backup pump will not activate upon resetting the circuit breaker, or ac power must be secured prior to resetting the circuit breaker. Damage to the current limiters may occur and will be indicated by a loss of all loads on No. 1 ac primary bus.
Backup pump initiation with AFCS heading hold engaged (AFCS TRIM switch on, pedal microswitch not depressed) may cause AFCS heading hold failure, indicated by AFCS control panel HDG fail advisory and an AFCS DEGRADED flashing caution light. Should the malfunction occur, system operation can be restored by pressing one of the fail advisory mode reset switches.
NOTE:
FLIR failure may occur if the backup hydraulic pump is turned on with FLIR operating.
Describe the backup pump
The backup hydraulic pump is identical to the No. 1 and No. 2 hydraulic pumps except that it is powered by an ac electric motor. An internal depressurizing valve reduces the output pressure of the backup hydraulic pump to aid startup of the electric motor. When power is supplied to the pump, this valve is closed and 3,000-psi pressure is supplied to the hydraulic system. After 4 seconds on APU or external power, or 0.5 second with either main generator on, the pump will energize. The automatic low-level sensing switch, mounted on top of the pump, closes when fluid level is low, causing the BACKUP RSVR LOW caution to appear. The BACKUP HYD PMP switch is a three-position toggle switch located on the miscellaneous switch panel (Figure 2-36). Backup pump operation is controlled by a combination of switch position and weight on/off wheels
How does the Backup Pump operate in the different switch positions with weight on wheels?
With weight on wheels and BACKUP HYD PMP switch position: OFF — The backup pump remains off. ON — With the No. 1 and No. 2 hydraulic pumps operating normally, the backup pump recirculates hydraulic fluid to and from each transfer module and maintains pressure in the APU accumulator and rescue hoist systems, as required. The backup pump remains on until it is secured. AUTO — The backup pump automatically maintains hydraulic pressure to the No. 1 and/or No. 2 hydraulic systems, including the second stage of the tail rotor servo (as required for hydraulic system pressure and/or fluid losses detected by the LDI system
How does the Backup Pump operate in the different switch positions with weight off wheels?
With weight off wheels and BACKUP HYD PMP switch position:
OFF or AUTO — The backup pump automatically maintains hydraulic pressure to the No. 1 and/or No. 2 hydraulic systems, including the second stage of the tail rotor servo (as required for hydraulic system pressure and/or fluid losses detected by the LDI system). The backup pump also maintains hydraulic pressure in the second stage of the tail rotor servo when the TAIL SERVO switch is placed to BKUP.
ON — With the No. 1 and No. 2 hydraulic pumps operating normally, the backup pump recirculates hydraulic fluid to and from each transfer module and maintains pressure in the APU accumulator and rescue hoist systems, as required. The backup pump remains on until it is secured
When is the backup pump automatically engaged?
- Loss of No. 1 hydraulic pump pressure (#1 HYD PUMP caution).
- Loss of No. 2 hydraulic pump pressure (#2 HYD PUMP caution).
- Loss of No. 1 hydraulic reservoir fluid (#1 RSVR LOW caution).
- Loss of pressure to the first stage of tail rotor servo (#1 TAIL RTR SERVO caution).
How does the utility module work?
The utility module routes hydraulic fluid from the backup hydraulic pump to the No. 1 and No. 2 transfer modules, second stage of the tail rotor servo, rescue hoist, and APU accumulator. A pressure switch is located on the module sensing backup hydraulic pump output pressure and, if above a prescribed value, closes a circuit causing the BACKUP PUMP ON advisory to appear. A priority valve is installed between the utility module and the rescue hoist to restrict hydraulic fluid to the rescue hoist in the event that backup hydraulic pressure decreases below a prescribed value. The utility module incorporates a velocity fuse, which secures fluid flow to the APU accumulator if flow rate exceeds a prescribed limit
Describe the LDI.
The Hydraulic Leak Detection/Isolation (LDI) system attempts to maintain hydraulic pressure to the primary and tail rotor servos by minimizing loss of hydraulic system pressure and/or fluid should a hydraulic system malfunction occur. The LDI system incorporates two logic modules that receive inputs from the hydraulic system automatic low-level sensing and pressure switches and command actuation of the hydraulic system shutoff valves
Describe the logic modules in the hydraulic system.
Two logic modules continually monitor the operation of the hydraulic systems via inputs received from the hydraulic pump automatic low-level sensing switches and from the primary servo, tail rotor servo, and pilot-assist servo assembly pressure switches. When the LDI system detects a low fluid level condition in one of the hydraulic pumps (#1 or #2 RSVR LOW caution), the logic modules automatically operate the required shutoff valve(s) to isolate the leak. If the leak is in the No. 1 hydraulic system, the LDI system assumes that the leak is in the first stage of the tail rotor servo and secures hydraulic pressure to that stage. This turns on the backup pump, pressurizing the second stage of the tail rotor. If the leak is in the No. 2 hydraulic system, the LDI system assumes that the leak is in the pilot-assist servo assembly and secures hydraulic pressure to the assembly. If the leak continues after the initial isolation of the first stage of the tail rotor servo or the pilot-assist servo assembly, the LDI system will reopen the respective shutoff valve. The pilot must then secure the affected primary servo, using the SERVO switch, to isolate the leak.
What criteria must exist to initiate the hydraulic leak test?
- Ac power.
- BACKUP HYD PMP switch in the AUTO position.
3. All hydraulic reservoirs full.
4. Weight On Wheels (WOW).
5. Rotors engaged
How does the HYD LEAK TEST work?
The three-position HYD LEAK TEST switch is located on the upper console. Switch positions are TEST, RESET, and NORM. If in the TEST position and the above criteria are met, an electrical signal is sent from the logic modules, closing the first-stage tail rotor and pilot-assist module shutoff valves and testing the RSVR low circuitry. The logic modules then take their normal action for such a condition. In order to restore normal operation to the hydraulic leak detection system following a hydraulic leak test, the HYD LEAK TEST switch must be placed to the RESET position momentarily, then back to the NORM position.
