Comparison of The Structure And Sealing of Wedge Gate Valves And Parallel Gate Valves

I. Comparison of Structural Characteristics

(I) Wedge Gate Valve

The gate of a wedge gate valve is wedge-shaped, and its sealing surface forms a certain angle with the vertical centerline (usually 2°52', 3°30', 5°, 10°, etc.). This design enables the gate to wedge into the valve seat when closed, forming a tight seal. According to the different types of gates, wedge gate valves can be divided into three forms: single-gate, 

double-gate, and elastic-gate. The single-gate structure is simple, but it requires a high precision of the angle of the sealing surface. The double-gate structure is complex, but it requires a lower precision of the angle of the sealing surface and can compensate for the wear of the sealing surface through adjustment. The elastic-gate combines the advantages of the single-gate and can compensate for processing deviations through minor deformations.

(II) Parallel Gate Plate Gate Valve

The sealing surface of a parallel gate plate gate valve is parallel to the vertical centerline, that is, the two sealing surfaces are parallel to each other. Its gate is usually of a double gate structure, with a thrust wedge or spring device in the middle, and the sealing is achieved through the pre-tightening force of the wedge or spring. This structure makes the processing and maintenance of the gate of the parallel gate plate gate valve relatively easy, and the external force required during the opening and closing process is relatively small.

II.Sealing Performance Comparison

(I) Wedge Gate Valve
The wedge gate valve has excellent sealing performance, mainly relying on the tight combination of the wedge-shaped gate plate and the valve seat to achieve sealing. Its sealing surface is usually made by surfacing hard alloy, which is wear-resistant, high-temperature-resistant, has good anti-galling performance and a long service life. In addition, the angle design of the sealing surface of the wedge gate valve enables it to maintain good sealing performance under high-pressure and high-temperature working conditions, and it is suitable for pipeline systems with various pressures and temperatures. However, when the temperature changes greatly, the gate plate of the wedge gate valve may be wedged due to thermal expansion, resulting in difficult opening.
(II) Parallel Gate Plate Gate Valve
The sealing performance of the parallel gate plate gate valve is relatively weak, mainly relying on the pre-tightening force between the gate plate and the valve seat to achieve sealing. Its sealing surface is usually designed as a flat surface. Although it is convenient for processing and maintenance, its sealing performance is not as stable as that of the wedge gate valve under high-pressure or high-temperature working conditions. However, through optimized design, such as adopting a two-way forced pre-tightening sealing structure, the parallel gate plate gate valve can also improve the sealing reliability to a certain extent.