NATOPS CH2.8 Hydraulic System Flashcards Preview

Princess' MH-60R HAC Tutorial (MAY20) > NATOPS CH2.8 Hydraulic System > Flashcards

Flashcards in NATOPS CH2.8 Hydraulic System Deck (21)
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To what do the hydraulic pumps provide pressure?

Three hydraulic pumps provide pressure to the hydraulic omponents of the flight control system, the APU accumulator, and the rescue hoist system

A utility hyydraulic pump also provides pressure for the sonar reeling machine


What is the hydraulic system pressure?

With the exception of the Pitch and Roll trim actuators in the pilot-assist servo assembly (1000 psi) all components of the hydraulic system receive 3000 psi from the hyd pumps


What does the No. 1 Hyd Pump operate?

The No. 2 Hyd Pump?

The No. 2 Hyd Pump operates the first stage of the primary servos and the first stage of the Tail Rotor Servo

The No.2 Hyd Pump operates the second stage of the priamry servos and the pilot assist servo assembly


What is the purpose of the Trasnfer Modules?

They route fluid from the Hyd Pump to the appropriate servos and system (TR or PASA)

They also contain the logic to route backup pump fluid in the event of a leak and to secure fluid from from the main pump when the Servo Switch is used


How do you supply/remove power to the various parts of the Pilot Assist Servo Assembly?

Hydraulic pressure (1000 psi) to the pitch and roll trim actuators is controlled by the TRIM push button

Hydraulic pressure (3000 psi) to the Boost servos and SAS actuators is controlled with the SAS/BOOST push button


What does the Backup Pump provide pressure for?

The backup pump provides hyd pressure to the

  • No.1 / No.2 hyd systems prior to rotor engagement
  • Pressure to the rescue hoist system
  • Recharges the accumulator
  • Emergency pressure to the No.1 / No.2 Hyd systems and the Second Stage TR Servo


If the Backup Pump CB is popped, how do you reset it?

If the CB is out and a condition exists that requires the backup pump to operate, either the hydraulic system must be configured so that the backup pump WILL NOT activate upon resetting the CB (setting the Switch to OFF satisfies this on the ground) or AC power must be secured, prior to reseting the CB.

Damage to the current limiters may accure and will be indicated by a loss of all loads on the No.1 AC Primary bus



What is different about the backup pump?

How long does it take to energize?

The backup pump is powered electrically and requires a depressurizing valve to reduce output pressure until the pump can supply the full 3000 psi

It takes 4 sec on APU/External power, or 0.5 sec with either main gen on to energize


Describe how the backup pump will react to the various switch positions

On the ground

  • OFF: Pump stays off
  • ON: Pump stays on until secured
    • If Main hyd pumps are operating backup pump will keep pressure in APU accum and rescue hoist, and circulate fluid to transfer modules
  • AUTO: Pump automatically maintains pressure to No.1/No.2 Hyd systems and TR servo as required

In flight

  • OFF or AUTO: Automatically maintains pressur to No.1/No.2 hyd systems and TR servo as required
  • ON: Pump stays on until secured
    • If Main hyd pumps are operating backup pump will keep pressure in APU accume and rescue hoist, and circulate fluid to transfer modules


How long does the backup pump run to charge the accumulator?

When the APU accumulator is low and the backup pump is activated, it will run continuously for at least 90 sec (180 sec if winterization kit is installed) regardless of the switch position


When will the backup pump automatically be initiated?

  1. Loss of No.1 Hyd Pressure (#1 HYD PUMP caution)
  2. Loss of No.2 Hyd Pressure (#2 HYD PUMP caution)
  3. Loss of No.1 Hyd Reservoir fluid (#1 RSVR LOW caution)
  4. Loss of pressure to the first stage tail rotor servo (#1 TAIL RTR SERVO caution)


What does the Priority Valve do?

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


Describe the function of the Velocity Fuse

The velocity fuse, installed in the utility module, secures fluid flow to the APU accumulator if the flow rate exceeds a perscribed limit

(if you have a slow leak in the accumulator it isn't going to help you any)


What is the purpose of the Leak Detection and Isolation system?

The LDI is designed to assist in the isolation of hydraulic leaks


When and how does the LDI work?

What if it didn't work?

if the LDI detects a low fluid level condition in one of the hydraulic pumps it will attempt to isolate the leak.

If the leak is in the No.1 Hyd system, the LDI assumes the leak is in the first stage of the tail rotor servo and secures hyd pressure to that stage (This turns on the backup pump pressuring the second stage servo)

If the leak is in the No.2 Hyd system the LDI assumes the leak is in the Pilot-assist servo assembly and secures pressure to that assembly

If the leak continues after the initial isolation, the LDI system will re-open the respective shutoff valve after which pilot action is required (EP)


Whats required after shutting down the Helo due to a RSVR LOW Caution?

You need to cycle the HYD LEAK TEST switch, in order to reset the LDI logic


Whats required to run the Hyd Leak Test?

  1. AC Power
  2. Backup hyd pump switch in AUTO
  3. All Hyd reservoirs full
  4. Weight on Wheels
  5. Rotors Engaged


What if you accidentally activate the Hyd Leak Test in flight?

The test will not initiate because the weight on wheels switch is not actuated, however the system will "remember" that the switch was activated and is likely to initiate the test as soon as you land

To prevent this place the Backup Hydraulic pump in the OFF position until you are ready for it


What cautions will appear during a successful Hyd Leak Test?

  1. #1 RSVR LOW
  2. #2 RSVR LOW
  4. SAS


What does the Utility Hyd Pump power?

When does it do so and at how much pressure?

The Utility Hydraulic system operates the sonar reeling machine and does so only when the main transmission is turning. 

When deenergized the system operates at a reduced power of 1000 psi for recirculation and cooling, when powered system pressure increases to 3000 psi


What do you do if you don't need the Utility Hyd Pump

When use of the sonar reeling machine is not required, the UTILITY HYD PUMP switch SHOULD be OFF