Miniature fittings enhance airline beverage service

July 22, 1989
Designers increasingly rely on pneumatics for clean, fast, reliable, and economical automation systems.

A new beverage-dispensing cart eliminates the need for bottles and cans.

Beverage service aboard commercial aircraft has changed little since the 1950s. Flight attendants wheel a mobile service cart filled with metal cans to each passenger. With an increasing focus on cost and weight reductions, this traditional method will soon be replaced with a new system from Sterling Beverage Systems, Newnan, Ga. Sterling has designed and received FAA certification for a beverage-dispensing cart that promises dramatic cost savings for the airline industry. The system works similar to the postmixed dispensing systems used for many years at high-volume soft drink vendors such as McDonald's and Burger King.

The cart dispenses up to 14 carbonated and noncarbonated beverages, including soda, juice, tea, and water. It's powered by a cylinder of CO2 gas similar to those used to supply oxygen in the event of cabin decompression. The cart carries soda syrup in recyclable plastic bottles. Chilling carbonated water and syrup below 40?F before pouring over ice enhances carbonation. Beverage-dispensing heads at both ends of the cart allow two flight attendants to use the cart at the same time. Fully loaded the cart weighs approximately 210 lb.

Potential cost savings are substantial. A major U.S. airline currently uses more than 50,000,000 beverage cans per year and each can is handled many times before being discarded. A typical 12 oz soda can contains 10 oz of water. The Sterling system eliminates the need to carry this extra weight as water is taken, as needed, from the aircraft water supply. The system is estimated to reduce the nonproductive fleetwide aircraft load by 80,000 lb/day which, in turn, reduces fuel consumption. Further cost savings are realized because syrup costs less than cans.

Sterling also estimates a 50% reduction in flight attendant beverage-service workload. The attendant is freed from searching for the appropriate can, slowly pouring the warm drink over ice and waiting for the foam to subside, and then collecting and disposing of the empty cans. Faster beverage service improves passenger satisfaction.

The limited space available for the dispensing system, water, and syrup requires miniature, leak-free connections with both English and metric threads. Thirty standard and customdesigned products from Beswick Engineering Co., Greenland, N.H., have been specified on the beverage cart. These include pressure regulators, quick disconnects, pipe fittings, straight thread O-ring face seal fittings, breathers, and check valves that handle CO2, air, and syrup.

The compactness, reliability, and leak-tight capability of Beswick products are particularly important to the design. Most miniature fittings rely on gasket seals instead of captured Oring face seals. Three major problems with gasket-style fittings are leaks, loose connections, and excessive assembly time. Overtightening a gasket fitting can tear or extrude the gasket. This results in fluid leakage. On the other hand, if the assembler gingerly tightens the fitting to prevent tearing, the fitting is likely to come loose in service. Thread sealants reduce the chance of leakage and loose connections but this adds assembly time and cost, and thread sealant can plug orifices or contaminate other components. Often gaskets are supplied separate from the fitting and must be installed onto the fitting prior to assembly. This hidden cost often goes unnoticed by the customer.

Beswick fittings take full advantage of the sealing capabilities of elastomeric O-rings. The fittings incorporate a precision-machined gland (groove) that retains an O-ring. Groove height is less than the O-ring cross section so when a fitting screws into place, the O-ring squeezes between the groove and mating surface. An elastomeric O-ring resists this squeeze and exerts a sealing force on the mating surfaces. In addition, the bottom surface of the gland contacts the mating surface during installation. This provides sufficient preload so the fitting will not come loose in service.

Information for this story was supplied by Michael Donati, Beswick Engineering, Greenland, N.H.

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