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The ability to handle high pressures, yet light and flexible enough were the essential requirements when the Penske company were sourcing components for their high-tech knee brace. Clearly, the physical demands placed upon the materials and components within such a product are unusual, if not unique.
The Lee Minstac system of tubing and fittings were chosen by Penske because of their ability to be flexible, yet strong enough to provide a leak-free performance, even under high pressure. On one side of the knee brace is a cylinder which acts as a reservoir for the hydraulic fluid, while on the other side of the brace is another cylinder which acts as a damper to control the rate of movement of the knee joint.
The basis of the Minstac tubing connection system is a collet-lock device which allows the end of the Teflon tubing to be chamfered and then threaded into a specially designed collet. This assembly provides a leak-proof connection from the Teflon tubing to the wide range of Minstac components and fittings, all without the problems associated with Teflon’s cold flow characteristics.
The Penske knee brace features .156 Minstac fittings which are used with 0.156” outside diameter Teflon tubing and a 0.250-28 UNF fitting end. An internally threaded collet grips the outer diameter of the Teflon tubing end, preventing cold flow. The chamfered end of the tubing is pressed against one end of the ferrule by the collet, while the other end is pressed against the sealing surface in the boss by a coupling screw.
Minstac tubing end connections are available in three standard outside diameter sizes, 0.062”, 0.125” and 0.156”, with one or two fitting ends installed to satisfy most fluid handling requirements. Special lengths and fitting assembly tool kits are also available. Latest additions to the product range are the MIN-LOK coupling screws which have lock wire holes for high vibration applications.
