pressure pipe blowing off

Hi, the problem that I have is the small diameter (1/4 inch aprox) pressure pipe from the non return valve on the side of the tank to the pressure switch/unloader valve, blows off its connection, its held on with a nut and olive (Ive tried cutting the pipe and a new olive), the compressor starts ok and runs but the pipe blows off after a few minutes and of course it doesnt build pressure, any ideas on the cause of the fault ? regards Geoff Belgium