HYDRAULICS

CONTROLS AND INDICATORS

Hydraulic system controls and indicators

flap lever is set at 0º.

operate

operates

indicates pressure produced by the #1 (leftscale) and #2 (right scale) electrically driven

standby hydraulic pumps

RIGHT

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Hydraulic system controls and indicators

oil pressure

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SYSTEM DESCRIPTION

Hydraulic system

Hydraulic power is provided by two main systems, designated number 1 and number 2. Each system operates independently with its own engine driven hydraulic pump, electrically operated stand-by pump and reservoir of synthetic hydraulic fluid. A power transfer unit (PTU), driven by the number 1 system, provides an additional source of hydraulic pressure to number 2 system to allow landing gear extension and retraction in the event of pressure loss from number 2 engine driven hydraulic pump. The PTU operates automatically in the event of number 2 engine failure and landing gear lever UP selection. Ground service connections are located in each nacelle for number 1 and number 2 system. A hand-operated system is provided for emergency extension of the main landing gear. Hydraulic quantity and pressure indicators for each system are located on the right pilot's instrument panel, as well as control switches for the standby electrical driven pumps and the PTU. Main hydraulic system

The main hydraulic system is composed of number 1 and number 2 systems. An engine driven pump operates each system; the left engine drives number 1 and the right engine drives number 2. Each system operates independently of the other. Nominal pressure for the main system is 3000 Psi. Number 1 main hydraulic system operates the following:

• Wing flaps

• Main wheel brakes

• Anti-skid control valve

• Lower rudder actuator

• Inboard roll spoilers

• Power transfer unit

Number 2 main hydraulic system operates the following:

• Landing gear extension and retraction

• Emergency/parking brakes

• Nose wheel steering

• Upper rudder actuator

• Outboard roll spoilers

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Standby hydraulic system

The standby hydraulic system consists of an electrically driven pump in each main hydraulic system. The standby pump is used to provide an additional source of hydraulic power during take-off and landing and in the event of an engine-driven pump failure. The standby hydraulic system is controlled either automatically by the flap handle or manually by two STBY HYD PRESS toggle switches on the right pilot's instrument panel. Normal operation of the standby system requires that the number 1 and number 2 STBY HYD PRESS switches be selected to the NORM position. The standby pumps operate continuously with the flap lever out of the 0º position. The pumps switch off when the flap lever is selected to the 0º position. When the STBY HYD PRESS toggle switches are selected to the 1 or 2 position (ON), the appropriate system stand-by pump is activated continuously, irrespective of the flap selector position. In the event of a low hydraulic fluid return pressure or a low hydraulic fluid volume in the number 2 hydraulic system, a pneumatically operated valve automatically isolates the rudder hydraulic circuits from the remainder of the number 2 hydraulic system. The number 2 standby hydraulic pump will continue to operate within this circuit and thus provide rudder control in the event of failure of both number 1 and number 2 hydraulic systems. Electric power to the standby hydraulic pumps is supplied by their opposite variable frequency AC bus. The number 2 system stand-by pump, however, will revert to its onside AC bus when its normal supply is lost or corrupted (under-frequency protection). This is indicated by illumination of the #2 SPU AUX PWR caution light.

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Hydraulic distribution schematic

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Hydraulic system schematic

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Power transfer unit

The PTU consists of a hydraulic motor, powered by the number 1 system, driving a pump in the number 2 system. During PTU operation there is no transfer of hydraulic fluid between the systems. The PTU provides hydraulic power to the entire number 2 hydraulic system. The PTU activates automatically in response to loss of number 2 engine oil pressure and a landing gear UP selection. The PTU switches off automatically when the landing gear is fully retracted. Operation of the PTU is indicated by illumination of the HYD PWR PTU SEL switch light (green) on the right pilot's instrument panel.

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Emergency hydraulic system

This system consists of a manually operated hand pump and independent reservoir and is provided solely for the emergency (alternate) extension of the main landing gear only. More information can be found in section 12-14 ‘landing gear’. Pressure and quantity indicators

Hydraulic quantity and pressure indicators for each system are located on the right pilot's instrument panel. Pressure indicators for the main system and the standby electrically driven pumps are provided. System hydraulic pressure is indicated on the MAIN indicator for both the number 1 and number 2 systems, normally the pressure generated by the main engine driven pumps. Hydraulic pressure from the standby electrically driven pumps is indicated on the STANDBY gauge. On the MAIN and STANDBY gauges, number 1 system is indicated on the left side and number 2 system is indicated on the right side. The hydraulic fluid quantity gauge indicates the quantity of fluid in each system's main reservoir. number 1 reservoir is indicated on the left and number 2 reservoir is indicated on the right. Emergency reservoir quantity is measured by a dipstick.

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NON-NORMAL INDICATIONS AND INDICATION

System operation

During non-normal operation of the hydraulic system crew members should be aware that the pressure indicated on the MAIN indicator(s) is system pressure, not solely engine-driven pump pressure. Loss of all hydraulic fluid may lead to erratic indications on the HYD QTY indicators. Caution lights

#1 ENG HYD PUMP

#2 ENG HYD PUMP

Indicates low output pressure (below 2000 Psi) from related system main engine-driven hydraulic pump.

Applicable ECL: Engine hydraulic pump #1/#2 failure.

Remarks: Caution light will remain ON and standby hydraulic pressure will be displayed on #1/#2 standby and main hydraulic pressure indicator.

#1 HYD FLUID HOT

2 HYD FLUID HOT

Indicates hydraulic fluid in related reservoir exceeds 109º C.

Applicable ECL: Hydraulic fluid hot #1/#2.

Remarks: If the conditions exist on ground because of high ambient temperatures, operate flight controls actuated by the related hydraulic system. Caution light goes out when fluid cools to 95º C

#2 SPU AUX PWR

Indicates failure of one of two AC power supplies to #2 system standby hydraulic pump.

Applicable ECL: SPU #2 auxiliary power failure.

Remarks: Pump continues to operate on opposite side AC power source. Maintenance check required prior to subsequent dispatch.

#1 STB HYD PUMP HOT

#2 STB HYD PUMP HOT

Indicates overheat of related system electrically operated standby hydraulic pump.

Applicable ECL: Hydraulic #1/#2 system failure.

Remarks: When pump motor cools to 160º C caution light will go out and pump may be selected on if needed

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