Written by IAPMO-it 7:12 am ASSE, Backflow Prevention

Atmospheric Vacuum Breakers (AVBs) Keep Passengers Safe

AVBs prevent dirty water from flowing into clean potable water

Safran has over 60 successful years of aircraft toilet development and manufacturing. There have been a myriad of challenges in the aircraft toilet world during that time. It all started with production of the recirculating toilet, which uses the “blue juice” or blue chemical in the toilet to help control odor and toilet bowl rinse. The recirculating toilets went into service in the late 1950s. There are many stories about the blue chemical and reports of “blue ice.” To correct this issue, a vacuum breaker on the rinse line from the service panel is installed (which is on the skin of the aircraft) to rinse the system inside the toilet tank. The reduced pressure outside the cabin during flight would pull moisture out of the toilet tank and the moisture would freeze on the service panel surface if the lavatory service technician did not install the rinse cap after servicing. This would cause the “blue ice” to form on the aircraft skin that would occasionally fall off during flight — sometimes with disastrous results.

In the late 1970s, Safran was one of the first to develop a vacuum toilet with improvements in odor control, corrosion control, single point of servicing, interior cabin flexibility, and hygienic clear rinse water, rather than the blue liquid from the recirculating toilets. However, the potable water connection needed to prevent dirty toilet water from flowing back into the clean potable water. This product innovation is the atmospheric vacuum breaker, or AVB. Safran used ASSE 1001Performance Requirements for Atmospheric Type Vacuum Breakers, specifications along with Publication 308, Standards of Sanitation for the Construction and Operation of Commercial Passenger Aircraft and Servicing and Catering Facilities, to develop Safran’s own AVB. (Publication 308 is the Handbook on Sanitation of Airlines published by the U.S. Department of Health, Education and Welfare Public Health Services.) The requirements for backflow prevention were nearly the same as with land-based toilets, except for the operating pressures, which were lower than land-based toilets. In addition, the toilet could be at almost any angle the aircraft could maneuver during flight.

Along with tests of the ASSE 1001 specifications at a level orientation, Safran also performed a tilt back test. During the test, the toilet bowl is filled with water and food coloring and then tilts in the worst possible angle and direction to induce backflow into the potable water system. In early tests, the toilet and a technician were in the back of a pick-up truck that drove in circles to simulate aircraft environment gravitational forces. The test is a success when the backflow volume of dyed water does not rise more than half of the critical height of the atmospheric vacuum breaker. The critical height is the distance from the spill line of the toilet bowl to the highest point in the atmospheric vacuum breaker, per the ASSE 1001 specification.

Safran later created a Galley Waste Disposal Unit (GWDU), which is a device located on the galley’s work surface and allows flight attendants to dispose food waste into the aircraft’s waste tank. The GWDU operates similarly to a toilet. The GWDU innovation arose when the airlines provided feedback that they needed a system to easily dispose liquids on the aircraft. The crew were using sink drains to discard unused coffee, tea, and other liquids through the drain masts. This created drain mast clogs and stains on the skin of the aircraft. The GWDU also uses an AVB to rinse the basin and aid in liquid and food waste movement into the vacuum waste system (i.e. the waste tank).

The requirements for the design of the atmospheric vacuum breaker ensure the proper separation of potable water from grey water on the aircraft. This keeps passenger and crew safe since the potable water is used to make tea and coffee, make steam in ovens for warming meals, for lavatory and galley hand washing, and for any other device using potable water on the aircraft.

Over the years of toilet development, Safran has made many evolutions and improvements to the atmospheric vacuum breaker, including the introduction of AVBs for bidets, decorative toilet shrouds to hide the atmospheric vacuum breaker, and improvements to materials and manufacturing methods, such as introducing lightweight composite parts with various heights and integrated design solutions. The atmospheric vacuum breaker design and integration continues to evolve to meet customer needs. ASSE 1001 and the latest specifications within ASSE 1098-2021Performance Requirements for Atmospheric Vacuum Breakers for Vacuum Toilet Assemblies and Galley Waste Disposal Units on Commercial Aircraft, provide the guidelines for the construction and validation of the designs to ensure the sanitation of the potable water on aircraft. Safran is proud to be one of the industry leaders who helped to define and implement this specification.

Article by Safran Cabin first appeared in Working Pressure magazine

Last modified: December 19, 2023