I was approached by Pope Pneumatics regarding a problem Brush Traction where having finding something to transfer compressed air from the door frame to a rubber seal for the door of the Euro Tunnel train that they were building at the time. Apparently thay had tried various types of flexible tubing but none had withstood the considered 8 years use on the test bed. The above valve I designed and built after an adjustment of the angles from my first prototype the valve withsood a 12 year use cycle and was still going strong. The two parts of the valve are retained by a circlip in an over sized hole allowing the parts to float,this allowed for discrepancy in the door or frame manufacture and also age wear. The spring I had made to fit the required area and maintaining ample strength to assert the pressure needed to seal the 25psi pressure. I also had the valve chrome vanadium plated to give the extra wear strength.