The hydraulic indication, for the flight crew, is done through the engine indicating and crew alerting system (EICAS). The hydraulic pressure, quantity, and temperature parameters, and electrical conditions are sent to the EICAS. These parameters and conditions are shown to the crew as EICAS messages or synoptic pages.

Each hydraulic system has a different indicating system which operates independently from the other systems. Each system has different transducers that send data about the pressure, the quantity, and the temperature to the EICAS. The data is shown on the EICAS hydraulic synoptic-page. Analog data is used to show the reservoir hydraulic-fluid temperature, the reservoir hydraulic-fluid quantity, and the hydraulic system pressure.

The flight crew uses the EICAS display when it is necessary to see an indication. The maintenance crew uses the EICAS display and the gauges to compare indications for functional tests, and other maintenance tasks. The EICAS messages display shown gives the related messages for the hydraulic power system.

The hydraulic pressure indicating system supplies electrical signals to the engine indicating and crew alerting system (EICAS) for hydraulic pressure. This data is given for each of the three hydraulic systems.

The data is shown on the HYDRAULIC synoptic page of the EICAS in pounds per square inch (psi). The hydraulic pressure indicating-system has interfaces with DC Power Center (DCPC), Flap Control Unit (FCU), HYDRAULIC Control Panel, Data Concentrator Unit (DCU), Remote Data Concentrator (RDC) and Proximity-Sensor Electronic Unit (PSEU). 

The hydraulic pressure indicating system includes the components that follow:

Hydraulic Pressure Transducer

There are three hydraulic pressure transducers found in the aft equipment compartment. The left and right hydraulic system pressure transducers are installed on each left and right pressure filter manifolds. The auxiliary hydraulic system pressure transducer is installed on the switching valve.

The pressure transducer monitors hydraulic pressure on the left, right, and auxiliary system. It then sends an electrical signal of that pressure to a mating connector on the wiring harness.

The pressure transducer contains a regulator, bridge, and amplifier. The amplifier increases the output of the transducer to a satisfactory level to send along a twisted pair cable to the remote data concentrator (RDC). A voltage signal is made in proportion to the applied pressure. The pressure shows in psi on the HYDRAULIC synoptic page of the EICAS.

The transducer is made for operation at 2,950 psi (20,339.66 kPa) nominal hydraulic pressure and withstands pressure transients to a maximum of 3,500 psi (24,131.80 kPa). The transducer is approved to 4,500 psi (31,026.60 kPa) proof pressure and breaks at 7,500 psi (51,711.00 kPa). 

 

Hydraulic Pressure Switch

There are a total of eight hydraulic pressure switches found in the aft equipment compartment. There are two types of pressure switches. There are seven pressure switches of the first type (P/N 967008-1). The auxiliary DC motor pump (DCMP) control pressure switch is of the second type (P/N 966996-3).

The pressure switch P/N 967008-1 uses a two-pole, two-position switch to supply two isolated output signals. The switch opens at 2,400 psi (16,547.52 kPa), maximum. While the pressure decreases, the pressure switch closes at 1,800 psi (12,410.64 kPa), minimum. These conditions are applicable for usual operation, with the fluid temperature 20 to 225°F (–6.67 to 107.31°C). The switches operate at 3,000 psig (20,684.40 kPa) nominal hydraulic pressure and are resistant to pressure transients to a maximum of 3,750 psig (25,855.50 kPa).

The auxiliary DCMP pressure switch P/N 966996-3 uses a one-pole, two-position switch. The pressure in the auxiliary hydraulic system changes from 2,500 to 3,350 psi (17,237.00 to 23,097.58 kPa). This pressure switch closes at 3,350 psi (23,097.58 kPa), maximum. While the pressure decreases, the pressure switch opens at 2,500 psi (17,237.00 kPa), minimum. These conditions are applicable for usual operation, with the fluid temperature range from –65 to 160°F (–53.93 to 71.17°C). The switch operates at 3,000 psig (20,684.40 kPa) nominal hydraulic pressure and is resistant to pressure transients to a maximum of 3,500 psig (24,131.80 kPa).

Closed switch contacts for all eight switches show an unsatisfactory pressure level while an open switch shows a satisfactory pressure. The proof pressure for the switches is 4,500 psig (31,026.60 kPa) and the break pressure is 7,500 psig (51,711.00 kPa).

There are five pressure switches for the left and right hydraulic systems. The left engine driven pump (EDP) pressure switch, the right EDP pressure switch, and the right DCMP pressure switch are found on the left and right pressure filter manifolds. The left DCMP pressure switch is found in-line, between the DCMP and the pressure filter manifold. The power transfer unit (PTU) pressure switch is found in-line and downstream from the PTU pressure port.

There are three pressure switches for the auxiliary hydraulic system found on the switching valve. They are the lower rudder pressure switch, the auxiliary DCMP control pressure switch, and the auxiliary accumulator pressure switch.

The EDP and the DCMP pressure switches monitor the output pressure from each pump. If the pressure is low, these switches send signals to the EICAS, which gives an indication of low pump pressure on the HYDRAULIC synoptic page. The pressure switch signals are also used in the crew alerting system (CAS) logic, which shows caution and warning indications.

The PTU pressure switch gives an indication of low pressure from the PTU, during PTU operation. It is also used in the CAS logic to give a HYD PTU FAIL caution message. The auxiliary system DCMP pressure switch controls the intermittent operation of the DCMP. The auxiliary accumulator pressure switch and the lower rudder pressure switch (for the lower rudder power-control unit (PCU)) are used to supply CAS logic signals for advisory indications of the auxiliary system. 

 

 

Each hydraulic system reservoir has a fluid quantity indicator assembly which includes a gauge for visual inspection and servicing of the reservoir. The indicator assembly also contains a quantity transmitter, which sends a signal to the engine indicating and crew warning system (EICAS). The hydraulic quantity indicating system shows the fluid quantity on the HYDRAULIC synoptic page and on the visual gauges as a percentage of full. The hydraulic quantity indicating-system has an interface with Remote Data Concentrator.

The hydraulic quantity indicating-system includes the component that follow:

Hydraulic Quantity Transmitter

There are three hydraulic quantity transmitters found on the hydraulic system reservoirs in the aft equipment compartment. The left and the right quantity transmitters are installed on each left and right system reservoir. The auxiliary quantity transmitter is installed on the auxiliary system reservoir.

The quantity transmitter is a device, which measures the quantity of fluid that is in the low-pressure storage chamber of the reservoir. The indication is by a visual gauge on the reservoir assembly. An indication is also shown as a display on the HYDRAULIC synoptic page of the EICAS. The transmitter senses the position of the low-pressure piston to measure the fluid volume in the reservoir. The reservoir piston moves gears that set a pointer on the visual gauge.

The reservoirs, because of their different volume capacities, have different gear ratios in the quantity transmitter mechanism. The left and right system quantity transmitters have spur gears that turns a one-turn, 500-ohm potentiometer. The auxiliary system quantity transmitter has a spur gear that turns a one-turn, 1,000Ω potentiometer. The potentiometers supply an electrical output signal to the remote data concentrator (RDC) to show the fluid quantity on the HYDRAULIC synoptic page of the EICAS.

The hydraulic temperature indicating system supplies the temperature data of the hydraulic fluid for the left, right, and auxiliary systems. The fluid temperature is shown on the engine indicating and crew alerting system (EICAS) hydraulic synoptic page in degrees Celsius (°C). Hydraulic high temperature conditions are also shown in the CAS message area of the EICAS. The hydraulic temperature indicating-system has interfaces with Reservoir,Switching Valve and Remote Data Concentrator.

The hydraulic temperature indicating-system includes the component that follows:

Hydraulic Temperature Transducer

There are three hydraulic temperature transducers in the aft equipment compartment The left and the right hydraulic system temperature transducers are installed on their system reservoirs at FS680.00. The auxiliary hydraulic system temperature transducer is on the switching valve at FS780.00.

The temperature transducer is a resistor temperature device (RTD). The sensor resistance changes as a function of fluid temperature. The applicable transducer range is –75 to 305°C (–103 to 581°F).

Hydraulic Pressure Indicating System

Theory Of Operation

The hydraulic pressure indicating-system has interfaces to EICAS through the remote data concentrator (RDC), the proximity-sensor electronic unit (PSEU), and the data concentrator unit (DCU). The hydraulic system sensors are the pressure transducers and the pressure switches. They are found where the data needs to be recorded. The EICAS uses this data to supply CAS messages (pressure switches) and show pressure data on the HYDRAULIC synoptic page (pressure switches and pressure transducers).

Displays

There are two types of data shown on the HYDRAULIC synoptic page of the EICAS to show the hydraulic pressure conditions. They are:

Analog Data

The analog data displays actual values for the hydraulic system pressure and is supplied from the pressure transducer. When hydraulic pressure is applied to the transducer, a signal is transmitted to the RDC which gives data to the HYDRAULIC synoptic page of the EICAS.

Discrete Data

The discrete data is used to show hydraulic flow paths and failed pumps and is supplied from the pressure switches. The left and right DCMP pressure, the auxiliary accumulator pressure, and the lower rudder pressure switches send their data to the RDC. The PTU pressure, the left and right EDP pressure switches send their data to the PSEU.

From the RDC and PSEU, the data is then sent to the DCU which has control logic to process this data.

The DCU sends its output to give indications on the EICAS synoptic page and also messages on the EICAS. The auxiliary DCMP control pressure switch is in-line with the DCPC to control the auxiliary DCMP.

When a grounded signal condition is supplied from the pressure switch, the signal is transmitted to the RDC, the flap control unit (FCU), or the PSEU. This signal is specified as a low hydraulic pressure. When an open signal condition is supplied from the pressure switch, the signal is transmitted to the RDC, the FCU or the PSEU. This signal is specified as a high hydraulic pressure. The discrete data sources of the hydraulic pressure switches shown in table.

Hydraulic Pressure Readout

The hydraulic pressure display is shown on the HYDRAULIC synoptic page in color.

For the left and right hydraulic pressure-indicating systems, the white color shows a correct hydraulic pressure signal and >3200 psi . The green color shows a correct hydraulic pressure signal and >1800 and ≤3200 psi. The amber color shows a correct hydraulic pressure signal and ≤1800 psi.

For the auxiliary hydraulic pressure indicating system, the white color shows a correct hydraulic pressure signal and >3500 psi. The green color shows a hydraulic pressure correct and >1 800 and ≤3500 psi. The amber color shows a correct hydraulic pressure signal and ≤1800 psi.

Hydraulic EICAS Messages

The HYD PRESS LOW warning message will show when the pressure of the left and right hydraulic system is ≤1800 psi.

The L (R) HYD PRESS LOW caution message will show when the pressure of the left (right) hydraulic system is ≤1800 psi.

The HYD PTU FAIL caution message will show when the PTU does not give pressure when it must.

The AUX HYD PUMP FAIL ON advisory message will show when the auxiliary pump does not stop to operate after 60 seconds.

The AUX HYD SYS FAIL advisory message will show when the auxiliary pump does not give pressure when it must.

The L(R) HYD DC PUMP FAIL advisory message will show when the left (right) DCMP does not give pressure when it must.

The L(R) HYD ENG PUMP FAIL advisory message will show when the left (right) EDP does not give pressure when it must.

The EICAS messages that follow are related to the hydraulic pressure indicating-system:

EICAS MESSAGE(S)	LEVEL (COLOR)
HYD PRESS LOW	WARNING (red)
L HYD PRESS LOW	CAUTION (amber)
R HYD PRESS LOW	CAUTION (amber)
HYD PTU FAIL	CAUTION (amber)
AUX HYD PUMP FAIL ON	ADVISORY (cyan)
AUX HYD SYS FAIL	ADVISORY (cyan)
L HYD DC PUMP FAIL	ADVISORY (cyan)
R HYD DC PUMP FAIL	ADVISORY (cyan)
L HYD ENG PUMP FAIL	ADVISORY (cyan)
R HYD ENG PUMP FAIL	ADVISORY (cyan)

 

 

Hydraulic Quantity Indicating System

The hydraulic quantity indicating system supplies the hydraulic fluid quantity that is contained in the left, right and auxiliary reservoirs. The system shows the reservoirs quantities on the visual gauges. While the fluid quantity decreases, the reservoir piston moves closer to the empty position in the reservoir. The reservoir indicator assembly senses the position of the piston as an indication of the fluid quantity in the reservoir. A visual gauge on the indicator assembly supplies the fluid quantity to the maintenance personnel.

For the left and right hydraulic quantity, there is a pointer on the visual gauge. The gauge has marks from 0 to 100 of percentage full in increments of 10. For the auxiliary hydraulic quantity, the gauge has an arrow mark that shows from 0 to 100 of percentage of full in increments of 5.

The system also shows the reservoirs quantities on the HYDRAULIC synoptic page of the EICAS. The hydraulic quantity transmitter sends an electrical output signal to the RDC. The fluid quantity shows as a percentage full on the HYDRAULIC synoptic page of the EICAS. The percentage display is accurate to ±2% of the reservoir fluid volume

The hydraulic quantity display is shown on the synoptic page with color. For the left fluid quantity, the white color shows a hydraulic fluid quantity signal 85%. The green color shows a hydraulic fluid quantity signal between 30 and 85%.

For the right fluid quantity, the white color shows a hydraulic fluid quantity signal 85%. The green color shows a hydraulic fluid quantity signal between 40 and 85%.

For the auxiliary fluid quantity, the white color shows a hydraulic fluid quantity signal 85%. The green color shows a hydraulic fluid quantity signal between 20 and 85%.

For the left, right, and auxiliary hydraulic systems, if there is an incorrect hydraulic fluid quantity signal, two magenta color dashes are shown.

Hydraulic Temperature Indicating System

The temperature transducer sends an electrical signal to the remote data concentrator unit (RDC). The hydraulic temperature is shown in °C on the HYDRAULIC synoptic-page of the EICAS in color. For the left and right hydraulic temperature-indication:

• The green color shows that the hydraulic temperature is correct and that the L HYD TEMP HIGH or R HYD TEMP HIGH caution is not set.
  
  
• The amber color shows that the L HYD TEMP HIGH or R HYD TEMP HIGH caution is set.

For the auxiliary hydraulic temperature-indication:

• The green color shows that the hydraulic temperature is correct and that the AUX HYD TEMP HIGH caution is not set.
• The amber color shows that the AUX HYD TEMP HIGH caution is set.

The L HYD TEMP HIGH or R HYD TEMP HIGH caution message will come on when the temperature is >97.60 °C (>207.68 °F). The AUX HYD TEMP HIGH caution message will come on when the temperature is >132.00 °C (>269.60 °F).

The EICAS messages that follow are related to the hydraulic temperature indicating-system:

EICAS MESSAGE(S)	LEVEL (COLOR)
AUX HYD TEMP HIGH	CAUTION (amber)
L HYD TEMP HIGH	CAUTION (amber)
R HYD TEMP HIGH	CAUTION (amber)

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