Ken Korane • Contributing Editor
The QDM3 connector from Beswick Engineering, Greenland, N.H., is said to be the world’s smallest dry-break quick disconnect. The ultra-miniature QDM3 consists of mating internal and external ends that, when connected, have an overall length of 33 mm. Hex width across flats is only 6.4 mm.
The quick disconnects are based on a dry-break design, sometimes referred to as “no-spill” technology. This configuration is a more sophisticated version of a standard double shut-off quick disconnect. Double shut-off designs have shut-off valves in both the internal and external sections. These shut-off valves retain pressure in both fluid lines when the assembly disconnects. However, these connectors are not truly “leak free.” Fluid can still leak out, usually from the external end, when connecting or disconnecting fluid lines under pressure.
Dry-break quick disconnects provide a level of sealing beyond that of double shut-off connectors. Dry-break versions ensure that the shut-off valves in both ends fully close prior to disconnection. Also, the two halves create a seal before the shut-off valves open during connection to prevent leakage or fluid spray. These quick disconnects typically have very low dead volume (the space between the internal and external ends when connected) to prevent trapped fluid from escaping or dripping when disconnected. This feature is especially important when handling liquids; or expensive, toxic or flammable gas where minimal leakage is paramount.
The QDM3 is made from 303 stainless steel, and Beswick quick disconnects are designed with O-ring seals to ensure leak-tight operation. Buna-N seals are standard, as they are economical and compatible with many fluids. Optional seal materials include EPDM and Viton; other materials, such as silicone and perfluoroelastomers, are also available to provide greater temperature compatibility or handle aggressive chemicals.
Maximum pressure rating is 500 psig while connected and 200 psig while connecting or disconnecting. Flow area is characterized as approximately equivalent to an 0.018 to 0.020 in. orifice, with a Cv of approximately 0.007 to 0.009.
They have M3 internal threads on both ends for attachment to fluid lines. Beswick offers M3 threaded barbed fittings for connection to soft tubing, and M3 compression fittings for use with harder tubing.
Miniature quick disconnects are used in a number of applications, including in analytical instruments. Such instruments are used to test various gases and liquids, and procedures often require the fluid lines be quickly connected and disconnected without losses or spills. Other applications range from use in medical devices and semiconductor manufacturing equipment to portable hydrogen fuel cells. Thanks to the small, compact size, they’re even being used by aerospace companies in microsatellites and UAVs.