Brief: Double expanding through conduit gate valve is one kind of bilateral forced sealing valve with the capability of protecting the sealing surface, this type of expanding through conduit gate valve can be widely installed onto pipelines and storage devices for oil products, natural gas and oil, and corrosive medium such as acid and alkali etc. Sealing Principle: Gear-driven device drives the stem making the main gate up and down, the sub-gate will move alone with the main gate under the force of link rod, Double expanding through conduit gate valve realize its on/off activity in this way, the gate will be expanded when the valve is fully opened or closed to control the medium. Gates Structures: The two-piece gates are on the start and end position of moving process, because of changing of main gate and sub-gate according to incline position making two sealing surface of two-piece gates bring closing and expanding action. These actions can realize effective sealing and protect the sealing surface during valve open. - When fully opened, the pair inclines of the two-piece gates will be expanded till they are stick to the seats preventing medium and impurity from entering. - During the process of opening and closing, the pair inclines of the two-piece gates will close to the two sides of valve ensuring the gates moving freely - When fully closed, the pair inclines of the two-piece gates will detach and making the two sides of gates closing to the sealing surface to enhance a perfect sealing Features: Full Bore Design making the Double expanding through conduit gate valve suitable to be placed on pipelines to be cleaned by tube cleaner, causing no block or damage to the valve itself and other fittings Floating seat structure design to realize flexible and rigid double sealing capabilities. Deposit weld high-hardness alloy onto sealing surface forming a metal to metal structure, both structures can realize bilateral enforced sealing. With unique top assembling design, professionals or well-trained maintainers can replace the valve trims online - without dissembling  When the Double expanding through conduit gate valve is fully opened or closed, the chamber isolates from medium completely, by this way, under an accident condition, open the empty valve and draining valve to relieve the pressure firstly, and then carry out the malfunction remove, drainage and packing replacement. When accidental leakage happened to sealing, relieve the pressure through grease injection, and the injection sealing gum into it, in order to carry out the next step, this method can only be used as an emergency management before taking measure. Because of absolutely bilateral sealing don't relieve the pressure through the sealing surface to pipeline when the pressure in chamber rises abnormally due to temperature rising or metallographic variation, but relieve it through safety valve placed on the valve body to keep safety for the pipeline and devices. Double expanding through conduit gate valve is with fire safe design to API 6FA or JB/T6899 The position of installation is flexible which can be vertically, horizontally reversely and obliquely installed. Manually operated valve is with hand-wheel or gear device. When the Double expanding through conduit gate valve is operated by actuator, different ways of operation can be adopted according to different customers' requirements and different situations. Such as pneumatic actuator, hydraulic actuated, electric actuated, to realize quick opening and closing, site and remote control and program control through computer. With pneumatic actuator, the valve can be opened and closed rapidly within 15S to finish the whole travel. Double expanding through conduit gate valve can be connected with pipelines through flanged or butt welded ends to ANSI, API, JIS, ISO and BS Standards etc.