The gate valve consists of a valve body, a gate, a valve stem, a valve seat, and a driving device. When opening, the driving device drives the gate to move upward through the valve stem, opening the medium passage. When fully open, the flow resistance is close to that of the pipeline. When closing, the gate moves downward and fits closely with the sealing surface of the valve seat to cut off the medium. Its sealing relies on forced sealing and the assistance of medium pressure. When closing, the driving device applies pressure to form the initial seal, and the medium pressure further presses the gate to enhance the sealing. However, the friction between the gate and the valve seat easily causes wear on the sealing surface.
The fully welded ball valve adopts a welded valve body, and its core components are the ball, the valve seat, the valve stem, and the actuating device. It realizes opening and closing by rotating the ball 90 degrees. When opening, the through-hole of the ball aligns with the pipeline, and the medium passes through unobstructed with extremely low flow resistance. When closing, the solid part of the ball blocks the passage. The sealing depends on the elastic valve seat, which closely adheres to the polished surface of the ball under the action of medium pressure or spring force. Moreover, the fully welded valve body prevents external leakage. The ball has little rotation friction, and the sealing surface has a long service life.
In terms of the opening and closing method, the gate of the gate valve has a large stroke, slow operation, and high driving force requirements. The ball of the fully welded ball valve rotates for convenient operation and is suitable for frequent opening and closing. Regarding the sealing performance, the sealing surface of the gate valve is easily worn, while the fully welded ball valve has better sealing performance and is suitable for scenarios with high-sealing requirements. In terms of the flow capacity, the gate valve still has an obstruction even when fully open, and the flow resistance is large at a small opening. The fully welded ball valve has a small flow resistance when fully open and accurate flow regulation. Therefore, the gate valve is mostly used in occasions where the opening and closing are not frequent and the sealing requirements are low, while the fully welded ball valve performs well in harsh working conditions such as long-distance oil and gas transportation.
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