Spherical seal friction own greater freedom in the gap to the extent permitted, so the installed accuracy is not required, the hollow shaft and equipment synchronized movement, the shell is relatively static, hollow shaft, ball and ball seat spring seal ring relative to the formation of spherical friction, wear ring seal to a certain thickness, put a new one to work. Fluid from the shell into the hollow shaft openings, the flow of equipment, leads from the inner tube (not one-way), but also in turn work, rotating joint cavity in the fluid medium can also be reached by mutual isolation.