11.17 Water and Waste

Potable Water System

• The potable water system stores, delivers, monitors, and controls potable (drinkable) water for galley and lavatory components.
• It consists of:
  • Water storage tanks
  • Distribution lines
  • Pressurization
  • Quantity indication
• Potable water is typically stored below the cabin floor, often in the cargo area sidewalls.
• Aircraft may have single or multiple tanks depending on the type.

Potable Water System Pressurization

• Pressurization is needed to move water from storage tanks to galleys and lavatories.
• A water tank pressurization system or an electric pump system achieves this.
• Normally the aircraft pneumatic system pressurizes the tank(s).
• Pressure pushes water through distribution lines.
• Air filters in the supply lines prevent contamination, often using a 10-micron filtration cellulose element.
• Check valves prevent reverse flow of water and air to the air supply.

Air Compressor

• An electrical air compressor can be activated when pneumatic bleed air isn't available, controlled by a pressure switch.

Pressure Relief Valve

• It prevents damage to the tank from over-pressurization.
• Located between the pressure switch and the water storage tanks.
• Ensure the pneumatic system is depressurized when replacing components in the potable water system.

Potable Water System Distribution

• Water tanks distribute water via supply lines and valves to lavatory and galley faucets.
• Lines are usually reinforced plastic hoses in a protective conduit, often behind cabin ceiling panels.
• Shut-off valves isolate sections for maintenance.
• Manual shut-off valves are located in each lavatory.
• Engineers connect/disconnect water lines to modular units during maintenance.
• Plumbing includes lines, valves, heaters, and drain/waste system components.
• Water lines run throughout the fuselage, requiring insulation or heating in cold areas, like heat tapes, inline heaters, and heated hoses.
• Electrical shut-off valves in supply lines can isolate forward or aft sections in case of leakage on larger aircraft.

Potable Water Servicing

• Servicing involves filling with fresh water and draining when necessary.
• Draining is required:
  • Before disinfecting
  • When parking in freezing weather
  • At least every three days to prevent bacteria growth
• Regular disinfection is standard after certain maintenance or contamination.
• Servicing is done via a water service panel (or additional drain panel) on the lower fuselage, covered by an access door.
• Main panel components:
  • T-handle
  • Fill fitting with cap
  • Water quantity indicator
  • Air compressor interlock switch
• Drain valve handle and port are on the drain panel.
• A fill hose attaches to a fitting, and a fill valve controls water flow into the tank.
• The quantity indicator is used to fill the tank.
• An overfill drain line runs from the top of the tank to the exterior.
• Tanks are typically filled until water exits the overflow.

Fill/Overflow Valve

• Allows filling of the passenger water system.
• Often a four-port machined body with a spring-loaded rotary core to prevent leakage.

Potable Water Quantity Detection

• Modern aircraft automatically stop water supply at a preselected quantity, managed by a quantity control unit.
• The unit receives the actual quantity signal from a transmitter and the preselected value from a cabin attendant's panel.
• It closes the fill/overflow valve when the actual quantity meets or exceeds the preselected value.
• A "full" light illuminates on the service panel.
• The quantity transmitter controls the water quantity indication on the attendant’s panel.
• A water quantity pre-selector allows choosing the amount of water to be pumped into the tanks.
• Aircraft without pre-selection have a water quantity indication on the service panel (gauge or lights).
• Simpler transmitters operate like reed switches in older systems.

Potable Water System Draining

• Water tanks/lines from galleys/lavatories are drained for maintenance/cleaning.
• Open drain valves and shut-off valves to remove water.
• Drain valves are operated manually.
• Large aircraft (e.g., Boeing 767) may have drain valve handles on both the water service panel and water drain panel.
• Pressurizing the system with pneumatic bleed air helps force water from drain ports.
• After air pressure exhausts, gravity draining continues if the fill/overflow valve remains open.
• Washbasins/faucets are self-vented to allow air entry for complete draining.
• The system must be completely drained if the aircraft is parked outside in freezing conditions.
• After draining, pressurize to ensure all water is removed, then close all drain/shut-off valves.
• A potable water tank drain valve is a two-port valve below the tank, controlled from the water service panel.

Lavatory Water System

• Components include:
  • A header (water distribution)
  • A manual shut-off valve (isolation during leakage)
  • A water heater
  • A mixer valve (temperature control)
  • A washbasin with faucets
• Except for the washbasin, components are under the sink.
• Water flows from tanks through the shut-off valve to the header.

Header

• Distributes water to the toilet, water heater, mixer valve, and faucet.

Mixer Valve

• Mixes cold water from the header with hot water from the heater for warm water at the faucet.

Mechanical Faucet

• Faucets are either mechanical or infrared controlled.
• Mechanical faucets provide hot, cold, or mixed water via a spout.
• Some mechanical faucets have two internal cartridge assemblies.

Mechanical Faucet Operation

• Some faucet types have a single water inlet for warm water from the mixer valve.
• Pressing the actuator starts water flow, which stops automatically after a few seconds when released.

Infrared Faucet

• Controlled by a reflective sensor unit with two lenses.
• When water is needed, the sensor opens a solenoid-operated shut-off valve on the mixer valve.

Water Heater

• Provides hot water to the washbasin in each lavatory.
• Installed in the water supply line to the mixer valve or faucet.
• Includes a tank/small reservoir, high-wattage electric heating elements, a thermostat and overheating protection.
• The tank holds about 1.5 liters (3 pints) of water.
• Features: manual on/off switch, indicator light, pressure relief valve, overheat switch, and sometimes a temperature select switch.

Wastewater System

• Removes used water from lavatory/galley washbasins and drains it overboard via drain lines/masts.
• An overboard type wastewater drainage system is used.
• Wastewater can also drain to a holding tank, typically the same tank used for toilet waste.
• Plumbing drains wastewater into the toilet tank.

Wastewater System

• Drain masts and wastewater lines are electrically heated to prevent freezing.
• Gravity and differential pressure between the pressurized cabin and the drain mast exhaust generate wastewater flow.
• Each lavatory has a drain valve with three positions: OFF, DRAIN, ON.
• Accessible in the lower sink cabinet, below the water heater.
• Galley and lavatory units are designed to drain spills/leaks through a floor port, drained overboard via a heated drain mast.
• Wastewater is sometimes called grey water, which excludes toilet waste.
• Grey water assists toilet flushing or is drained overboard.
• Wastewater drain masts are heated electrically or with warm pneumatic air.
• Heaters in some grey water drain masts have high heat in flight and low heat on the ground.
• Heated gaskets and blankets are used to protect waste drains/lines.

Toilet Waste System

• Removes waste from lavatories and stores it in tanks. Provides hygienic toilets and waste disposal.
• Two main types of systems:
  • Flush motor toilets
  • Vacuum toilet systems
• Modular lavatory installations are common, with flushing components inside the unit, including a waste holding tank.
• A waterproof floor pan with a drain forms the lavatory unit's floor.
• Tierods attach the unit to the aircraft structure.

Flush Motor Toilet

• Each lavatory has its own toilet unit, main componets are:
  • Flushing equipment with a flush handle
  • A flush motor assembly
  • A waste tank
  • Drain equipment
• Components are installed in the lavatory assembly.
• The flush handle activates a timer that controls a flush motor mounted on top of the toilet waste holding tank.
• The motor turns a pump, spraying a flushing agent into the bowl in a swirling motion, after the timed amount of flush time completes, the waste and agent drain into the tank below.
• A separator between the tank and bowl prevents splash and visibility of tank contents.

Flush Motor Assembly

• Includes an impeller pump that rotates in a filter basket when the motor is on.
• The flush motor is a high-power three-phase electric motor, controlled by a timer. Activated by pushing or rotating the flush handle.

Flush Motor Toilet Operation

• The waste tank contains a mixture of water and a chemical, allowing ~100 uses before draining via an external service panel.

Vacuum Toilet System

• Modern vacuum toilets differ from electric flush units and are not interchangeable.
• Electronically controlled by a Flush Control Unit (FCU) near the flush valve.
• The FCU opens/closes the valve and opens a rinse valve for potable water to rinse the bowl.
• Connected to the aircraft's central monitoring and cabin services systems.
• Vacuum systems suction waste from the toilet and deposit it in waste holding tanks.
• The system has two or more central waste tanks in the cargo area.
• Tanks have quantity sensing systems and full indicators.
• An electronic control module shuts the system down when full, providing indications to the flight attendant's panel and flight deck.
• Tank size/number depends on the aircraft type.
• The vacuum toilet system also includes a vacuum system, flushing components, and servicing components.
• Blue Ice forms if there is a leak at the waste drain valve assembly at altitude.

Toilet System Servicing

• Servicing components allow ground draining and cleaning.
• The waste tank is drained by pulling the drain valve handle on the service panel, after attaching a ground service cart to the drain outlet and removing the drain plug.
• The tank is cleaned by connecting a water pressure hose, which enters the tank through spray nozzles.
• Latest tanks have built-in separators for particle-free air expulsion during waste suction.
• A waste tank rinse nozzle is fitted at the top for rinsing during servicing.

Vacuum Toilet System Servicing

• Servicing is done from a central waste panel on the lower fuselage.
• The panel has a drain fitting and valve handle for each tank, plus ground flush line fittings for cleaning.

Flush Motor Toilet Servicing

• Individual service panels are located below the toilet area.
• The drain valve opens to drain the toilet. It's seated in a hole at the bottom of the tank with a spring-loaded telescoping guide tube enclosed by a rubber boot.
• After draining, the tank is flushed with clean water.
• Once drained, the chemical line from the service cart connects to the ground flush line fitting.
• This allows charging the tank with 13-31 liters of chemical solution, depending on the aircraft type.
• Avoid skin and eye contact with the chemical solution.
• Clean any spillage in the service area immediately.
• Wear Personal Protective Equipment (PPE).

Waste System Servicing Panel

• Lavatory waste tanks are serviced through the waste service panel, generally on the lower fuselage near the waste tank location.

Toilet Waste System Servicing

• To drain, flush, and pre-charge the waste system:
  • Open the waste drain cap.
  • Connect the waste drain hose to the drain fitting.
  • Push the push-to-open lever on the valve assembly to open the inner door, which also opens a proximity switch to cut off the vacuum blower.
  • Pull T-handles to empty the waste tank(s).
  • Connect ground flush lines to rinse fittings.
  • Flush each tank (22-45 L of water, depending on the aircraft type).
  • Drain each tank of flushing liquid.
  • Push up each T-handle to close the waste tank drain ball valve.
  • Wait one minute.
  • Remove waste drain hose.
  • Close the waste drain cap.
  • Add pre-charge chemical to each tank.
  • Disconnect flush lines and allow to drain.
  • Close rinse fittings cap.
  • Close the service panel
• Ensure lines have drained before closing caps to prevent freezing.
• Rinse lines and waste tank drain lines are not heated.

Corrosion Aspects

• Detecting water leakages early is important.
• Corrosion control is effective against aircraft structural failures, decreases load-carrying, leads to fatigue.
• Water in lavatories/galleys increases corrosion susceptibility.
• Although most structures are aluminium, some manufacturers include titanium structures.
• Waterproof flooring, catch basins, and drains help control water flow and reduce corrosion.

Anti-Corrosion actions

• Corrosion Preventative Fluids (CPFs) applied to the structure
• Floor panel clips taped to prevent scratching
• Floor panels cushioned to prevent damage
• Floor panels sealed to prevent fluid entry
• Moisture barriers applied over the entire area.
• Leaks in the toilet system traced and fixed early.
• Use Corrosion Preventative Fluid (CPF) in well-ventilated areas and wear face masks.
• Consult the Aircraft Maintenance Manual (AMM) before application.
• On all toilet systems, leaks must be detected and rectified early.
• Pay attention to bilge areas located under galleys and lavatories
• Investigate water coming from lower bilge drains.
• Clean these areas frequently and maintain the protective sealant/paint finishes.
• Find the source and rectify the fault.