Plastic crown means leak free joints

Tom Shelley reports on a novel snap together, medium to high pressure pipe joint that is ideal for low cost mass production A crown shaped plastic part is key to a very low cost, push to connect, pipe connector that is leak free up to working pressures of 250bar and temperatures of 250 deg C. As well as being quick to connect, it is also demountable using a simple tool, and occupies much less space than conventional pipe fittings. It is presently at the pre-production evaluation stage with several automotive majors. The "High pressure quick connect" is one of the latest developments to come out of Oystertec, a €200 million per year UK based innovation company. Sealing is by a conventional 'O' ring on the end of the tube. The breakthrough innovation is in the way the connector is firmly held in place so that once inserted, the element with 'O' ring on it does not move. This is effected by means of a retaining ring, equipped with a number of flat spokes on its outer end which engage on the inside of a tube bead or retaining ring. The flat spokes, which open out in the same manner as a partially opened umbrella, are kept pressed outwards by means of a locking cap. Connection takes only seconds, and requires no use of special tools. The design is being licensed to large scale manufacturers, some of whom are specifying that the retaining ring be made in yellow plastic. If any yellow is visible after connections have been made, it is immediately apparent that a connector has not been pushed home. No visible yellow means that it is correctly in place. Because connections do not require application of a spanner or other tool, pipe connections can be placed much closer together, saving space. Disconnection requires removal of the locking cap, and insertion of a tool with an internal conical profile to compress the spokes, after which the pipe may be withdrawn. According to Brendan Johnston, Oystertec's automotive division director. Connectors fitted with nylon retaining rings may be rated to 250bar and 250 deg C, although burst pressure is up to 800bar. Applications are seen in braking systems, at pressures up to 200bar, power steering systems up to 120bar, and air conditioning systems at 40 to 100bar. On an impulse test, one of the connectors has so far been through 800,000 cycles at 128bar without failure. Tensile tests range from 5300N to 6000N while insertion force is as low as 50N to 67N. There are now some 600 sets on pre-production test cars. One on a turbo charged engine has now been in service for 18 months. The company is currently looking for further non-exclusive licensees. Oystertec Pointers * Connectors may be attached in seconds without tools * Working pressures are up to 250bar, although burst pressures are up 800bar * Connectors may be placed closer together than with conventional designs * The connectors do not leak * Connectors may quickly be disconnected with the help of a simple tool