Eccentric half ball valve is developed based on absorbing overseas. The structure is eccentric-titght principle through transmission gear to achieve the purpose or tightening , adjusting closing. Vice-seal  is metal surface ring with hard surface  contact sealing . The double eccentric structure will be located in ball sroring room and make the flow corss-section large  and the valve will not be washed . When closed the valve dise will not be washed and when open the valve disc ball surface willasymptote along valve seat to remove the scalinng obstac les and achievereliable seal . It is effective especially to the mixed flow transportation separated out of two mixed flowing easily scaling solids. The secondfeature is that the half ball of valve is double metal and different alloy overlaid on the base matal; the valve seat  is also overlaid by special treatment of retiement to make the sealing surface different types of anti-corrosion, wear-resistant, high-strength and so on to meet the needs of different occasions. The third feature is  tight seal to achievezero leakage at transmission of harmful gases. The forth feature is that vice seal left compensation amount. After the valve seat is wore ( the rigidity of valve seat is lower than of the valve disc ),when move alittle affer closing , the seal will be still reliable to extend the useful life. Besides, the valve is still useful when the users screw off the pressed nut or adjust or change the valve seat to avoid the short-coming of existing valves seal invalidation results in the while valve scraps. So overlaid different alloy (or assembly ball ) double mate vice-sael can be applied to dfferent industrial sectors of wear-resistant corrossion- resistant, high temperature and so on as well as strictly seal requirements. The main purpose and features of product.