A330/A340 Lavatory Waste System

Dear All,


We are going to brief some information regarding the waste system installed on A340/A330. Almost it has the same principle on most Airbus aircraft. A question always has been asked by people. This question is How we can get rid of the waste of passengers in the toilet. Here below we can find some information related to this subject.

Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.

The vacuum toilet system is based on the removal of the waste by suction into the waste holding tanks. Inflight the suction pressure is obtained by the differential pressure between the cabin and the waste holding tank. While on ground or at low altitude below 16000 ft altitude the suction is obtained by the vacuum generator because the differential pressure is so low.

The VSC receives signal from differential pressure switch to control the vacuum system generator according to the sufficiency of the differential pressure.

The flush control unit function is to control the flush cycle. When a failure occurs in the flush cycle then the flush control unit will send a signal to the VSC.

The water used to evacuate the waste from the bowl and to rinse the bowl is from the water system. The water valve is of solenoid type valve allows the water to be supplied through the ring into the bowl. Also this valve is equipped with anti siphon. The anti siphon make sure the water direction is to the water ring only.

The flush valve is an electrical motor operated valve. The flushing system is sequenced and monitored by the flush control unit. When the flush button pressed, electrical signal sent to flush control unit at which control the water valve, the flush valve, and the vacuum generator operation. Also the flush control unit interfaces with the VSC.

The left waste tank and its generator collect the waste from the left lavatories while the right waste tank and its related generator collect waste from the right lavatories.

The waste tanks are located in pressurized area of the aircraft aft of the bulk cargo compartment. On the waste tank there is a centrifugal separator that is used to separate water and waste from the air.

The air goes through a demister filter to overboard discharge line. When one waste tank has 80% while another has 70% then the level balancing valve can be opened through a handle on the right side aft of the cabin to use as much capacity of waste tanks during the flight.

Also between the tanks, there is an air shut off valve that also keeps air pressure between the tanks balanced. This valve is controlled by the VSC.

The VSC inhibits toilet operation during balancing or waste tank servicing. Also it interfaces with the PIM and the CMC.
Two of the three tanks are equipped with quantity transmitter the optional tank quantity isn’t displayed. The transmitters send its signal to the PIM via the VSC. Also there are full level sensors one in each tank that signals the PIM via the VSC to give the message LAV INOP.

The waste tanks are serviced from the waste service panel. Mechanically controlled cables will open the balancing valves and the drain valve through a handle. Every tank has its own rinse connection in the waste service panel. When the waste service panel door is opened, the VSC and the flush control unit will be de-energized.

When the waste tank balancing panel door opened, a signal will be sent to VSC that in turn will disable the toilets and opens the air shut off valve to carry out an air pressure balancing in the tanks too.

When balancing is required between the waste tanks, balancing required message appears on the PIM. Also during balancing valve open, VSC will generate message on the PIM LAV INOP BALANCING. Also in the balancing handle panel green light will illuminates.

If after four minutes the waste level balancing valves aren’t fully closed or a fault in the panel switch then the indication green light will start flashing. The VSC keeps the air shut off valve open and VSC will send a message to the CMC - Centralized Maintenance Controller- . LAVATORY CAUTION LIGHT illuminates.

I hope this infomration are helpful to understand the waste system.

B.Regards
Ayman Shak’ah
Licensed Aircraft Maint. Engineer

RB211 TRENT 700 / Fuel Circuit

Dear All,

Please find below how the fuel flow in RB211 Trent 700 fuel circuit following the schematic attached to this study.

Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.

The fuel system is used to receive fuel from the tanks and deliver conditioned metered fuel to combustion chamber. Also some fuel is sent to as a muscle pressure for the AOHE - Air / Oil Heat Exchanger - modulating valve and the VSV - Variable Stator Vanes - actuator system.

THE FUEL CIRCUIT:

The fuel enters the engine through the LP fuel valve in the pylon. It enters the LP stage of the fuel pump and then delivered to the FOHE - Fuel / Oil Heat Exchanger - to cool the engine oil and warm up the fuel. Then the fuel passes through LP filter and then it is delivered to the HP pump.

For the fuel LP filter, there is a bypass that will open in case the fuel filter is clogged.

Some of the HP fuel is delivered to the AOHE – Air Oil Heat Exchanger Valve – and the VSV – Variable Stator Vanes. Another part delivered to the FMU - Fuel Metering Unit-.

Inside the FMU, there is a PRESSURE DROP AND SPILL VALVE that will open in case of high unwanted fuel flow through the FMV. Then the fuel flow and pressure is controlled through the MV – Metering Valve – and the PRSOV - Pressure Raising and Shut Off Valve-.

The EEC - Electronic Engine Controller - controls the FMV to open or close by TM - torque motor -. This MV - Metering Valve - position fed back the EEC regarding its position through resolvers.

After the fuel metered through the FMV, it passes through the PRSOV and then supplied to 24 fuel nozzles after being filtered in the HP filter.

When the PRSOV is closed after engine shut down, there is a mechanically connected DUMP VALVE that will open allowing fuel remained in the manifold to be drained into drain collector tank. This unburned fuel will be sucked at next engine start by the LP pump.

The PRSOV is controlled independently from the EEC by the Master Switch. This will operate the torque motor to close the PRSOV whatever the EEC demand signal is.

In the FMU, there is an OPU – Over speed unit – that will close the PRSOV independently from the EEC if the EEC failure occurs.

Differential pressure switch installed through the LP filter signals the EEC in case of differential pressure is more than 5 PSI.

Fuel flow transmitter signals the EEC regarding the fuel quantity passed through it.

The FF - Fuel Flow - parameter is indicated on the ECAM SD - System Display - ENG PAGE AND CRUISE PAGE. Downstream the LP fuel filter there is fuel LP switch that give signal when fuel pressure less than 70 PSI. It indicates either low fuel pressure or the engine will shut down. As a result the failure will be transmitted to the CMC - centralized Maintenance Computer -.

Two fuel temp thermo couple are as the engine oil sensor signals the EEC as priority control for the heat management system (AOHE) control.

Two Microswitches are used to indicate PRSOV is closed during engine shut down or during turbine over speed test.

This was a short briefing about the fuel circuit in the Trent 700.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer