CAUTION
Whenever the No. 1 ac generator is inop-erative (failed, or not on line) and the BACKUP PUMP PWR circuit breaker is out for any reason, ac electrical power must be shut off before resetting BACKUP PUMP PWR circuit breaker. Otherwise, it is possible to damage the current limiters.

The backup hydraulic pump system supplies emergency pressure to the number 1 and/or number 2 hydraulic sys-tems whenever a pressure loss occurs. It also supplies pres-sure to the number 2 stage of the tail rotor servo in case of a loss of pressure in the .rst stage of the tail rotor servo or #1 RSVR LOW indication. This system supplies hydraulic pressure to all .ight control components during ground checkout. The backup system also provides a hydraulic pressure for automatic recharging of the APU start system accumulator. The backup hydraulic system pump module is driven by an electric motor which can be powered by any adequate three-phase ac power source. An internal depres-surizing valve in the backup pump module reduces the out-put pressure of the pump upon startup of the electric motor. This valve unloads the electric motor by reducing torque requirement at low rpm. After about 0.5 second when main generator is operating, or 4 seconds when operating from APU generator or external power, the valve is closed and 3000 psi pressure is supplied to the hydraulic system. This sequence reduces the current demand during backup system startup. Pressure sensing switches in the number 1 and number 2 transfer modules constantly monitor the pressure output of the number 1 and number 2 pumps. Loss of pres-sure initiates the backup operation. The system then pro-vides emergency pressure to maintain full .ight control ca-pability. A WOW switch on the left main landing gear provides automatic operation of the backup pump when the helicopter is in the air, regardless of BACKUP HYD PUMP switch position, and disables the backup pump ac thermal switch. A pressure sensing switch at the tail rotor monitors supply pressure to the .rst stage tail rotor servo. The backup pump can supply pressure to the .rst stage tail rotor servo if the number 1 pump loses pressure. This gives the pilot a backup tail rotor servo even with the loss of the primary hydraulic supply, or #1 RSVR LOW. If a leak in a primary servo system depletes the backup system .uid, the backup reservoir level sensing switch will turn on the BACK-UP RSVR LOW caution legend, and the pilot must manually turn off the leaking primary system.
2.37 HYDRAULIC LEAK DETECTION/ISOLATION SYSTEM.
The leak detection/isolation (LDI) system protects the .ight control hydraulic system by preventing the further loss of hydraulic .uid in case of a leak. The LDI system uses pressure switches and .uid level sensors for monitor-ing pump hydraulic .uid level, and pump pressure for pri-mary and tail rotor servos, and pilot-assist servos. When a pump module reservoir .uid level switch detects a .uid loss, the logic module follows the sequence detailed in Fig-
ure 2-13 to isolate the leak. To accomplish this, the logic module operates the required shutoff valve(s) to isolate the leak and turns on the backup pump when required. In the cockpit the RSVR LOW caution legend for that system lights. Backup pump and shutoff valve(s) operation is au-tomatic through the logic module. If, after the isolation se-quence, the leak continues, the leakage is in the stage 1 or 2 primary servos and the appropriate SVO OFF switch must be moved to the off position by the pilot. By placing the HYD LEAK TEST switch to TEST, all leak detection/ isolation system components are checked electrically. After a leak test has been made, the HYD LEAK TEST switch must be moved to RESET momentarily, to turn off caution and advisory legends that were on during the test. The

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2-40 Change 1

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Change 1 2-41

BACK-UP PUMP ON advisory legend will remain on for about 90 seconds. Refer to Chapter 8 Section II for test procedure. Except for the HYD LEAK TEST switch, the hydraulic leak system consists of components of 1st stage, 2nd stage and backup hydraulic systems. A WOW switch contact prevents hydraulic leak tests from being made in .ight. Power to operate the hydraulic leak test system is from the No. 2 dc primary bus through a circuit breaker, marked NO. 2 SERVO CONTR and dc essential bus through a circuit breaker, marked BACKUP HYD CONTR.
　
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