The Lip Seal with Back-up ring for 6D  Ball valve is mainly used for single-piston valve seat of 6D ball valve (temperature range IS-50~260 pressure range can reach 2500LB). A support ring is needed to protect the sealing lip when the reverse pressure in the middle cavity exceeds 1.33 times of rated pressure. When it is above 1500LB, need to add back-up ring the bottom.