ives the plug valve disc 90 degrees, when the handlewheel rotate unceasingly, the orbit valve's plug will be pressed downward, which will makes the two flanks of discopen, then the disc be firmly pressed on the seat and general valves be closed.3. When the handle wheel rotate in a negative direction, then plug will move upwards,which enable the disc separated from the seat, if rotate the handlewheel unceasingly at this time, the plug will drives the disc for 90 degrees, finally the plug's channe