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          Function and structure of pigging valve


          The pigging valve only plays the role of transmitting and receiving pigs when pigging the pipeline, and the pig is responsible for pigging and cleaning the pipeline.

          The structural feature of pigging valve is a new type of valve designed innovatively after modification and function addition based on the structural principle of T-type three-way fixed ball valve.

          The working principle of the pig valve is to place the pig into the inner cavity of the ball of the pig valve, and make 90% rotation through the ball in the mutually perpendicular three-way valve. When the sphere channel and pipeline channel are on the same axis, the pig is launched by the pig valve under the action of fluid pressure in the pipeline.

          According to different purposes, pigging valves can be divided into three categories:

          1: standard type (PC type)

          The aperture of the sphere is about 25% larger than the inner diameter of the connecting pipeline. One end of the aperture is provided with a stop strip that allows the medium to pass but can prevent the pig. When the pig is taken out and loaded, the fluid will be cut off for a short time.

          2: bypass type (Pb type)

          Bypass pigging valve shall be used when short-time cut-off of conveying medium is not allowed. The ball is larger than the standard pigging valve, and the pore size and structure are the same as those of the standard pigging valve, but the total flow section of the two bypass channels in the vertical direction of the pore axis is about 25% of the valve pore size section. The fluid flow will not be interrupted during the whole process of pig launching and receiving.

          3: isolated type (PS type)

          The aperture of the sphere is only about 3% larger than the inner diameter of the connecting pipe. In order to minimize the mixing of media upstream and downstream of the isolation sphere, an additional sealing ring is installed on the upstream side of the aperture baffle.

          The pigging valve is actually a T-type three-way fixed ball valve, which is installed and used in oil and gas long-distance pipeline. Therefore, the design specifications of pigging valves are in accordance with GB/T 19672-2005 technical conditions for pipeline valves, GB/T 20173-2006 pipeline inversion of belt conveyor system in petroleum and natural gas industry and API 6D-2008 pipeline valves. The design and calculation method of pigging valve is the same as that of conventional fixed ball valve.

          Pigging valve is a new type of valve with innovative design after improving and adding functions based on the structural principle of fixed ball valve. It realizes the opening and closing of the valve through the 90° rotation of the ball, realizes the sealing by using the double piston effect, and is designed into a double blocking and discharge function according to the characteristics of the ball valve, so that the medium in the body cavity can be discharged when the valve is fully open or fully closed. It inherits all the advantages of fixed ball valve and has the same adaptability as fixed ball valve. A branch pipe perpendicular to the center line of the flow channel is arranged on the side of the valve body, and a quick opening blind plate and a discharge valve are installed on the branch pipe, so that the pig can be conveniently sent to or taken out of the pig valve. One end of the sphere channel is provided with a stop strip which can block the passage of the pig and allow the medium to flow.