Fully plastic ball valve made from PTFE or a PTFE compound

摘要

Due to the cold-flow and thermal-expansion values of PTFE, it has hitherto not been possible to produce fully plastic ball valves from this material and the use of PTFE has therefore been limited to the ball seat rings and the lining of a metallic ball-valve housing, although the differing cold-flow and thermal-expansion values may result in separation or destruction of the coating. In our solution to the problem, the actual PTFE ball-valve housing (2) has not only the customary screw holes but also three holes to receive pins made from special steel or, alternatively, PTFE-glass (4) and two or more expansion seams (5a and 5b) recessed in all the way round. In the process of assembly, the two flanges (1a and 1b) are tightened fully by means of screws against the pins (4) in the housing (2). The length of the pins is chosen so that, after this operation, the seams can only be compressed by about 50%. This prevents the factors of cold flow and thermal expansion, which prejudice the functioning of the valve, since they are taken up by these expansion seams. <IMAGE>