There are four types of the most commonly used gates of gate valves, including rigid wedge single gates, flexible wedge single gates, wedge double gates and parallel double gates. No matter what kind the gate is, gate valves are sealed through the seal pressure produced by the wedge-shaped structure, and the seal pressure will become larger with rotating of hand wheels, which make the sealing performance of gate valves the most reliable. However, there is a narrow groove between the two valve seats in which media may be left if the gate valves are used under viscous medium conditions, medium conditions with a large number of solid particles or medium conditions where crystallization and solidification of media will easily occur. The remained media may even make gates of gate valves not to be completely closed.

Rigid wedge single gates
The structures of rigid wedge single gates are simple. When there are large machining errors of the gates, it is likely that the gate valves can not be sealed tightly due to the poor self-adjustment capacity and adaptability of the gates, which also makes the gates easily clamped too tightly when the gate valves are used under high temperature conditions. For gate valves with DN40 and below DN40, rigid wedge single gates are generally the default options for the valve manufacturer.

Flexible wedge single gates 
More complex than the structures of rigid wedge single gates, but simpler than the structures of wedge double gates and parallel double gates, the structures of flexible wedge single gates have certain self-adjustment capacities and adaptability. Thus, flexible wedge single gates are generally the default options for the valve manufacturer when they need to manufacturer gate valves with DN50 and above DN50.
 
Wedge double gates
Wedge double gates are the gates improved on the basis of flexible wedge single gates, the self-adjustment capacities and adaptability of which are strengthened. However, this structure is so complex that the production costs of gate valves with this gate type also increase. Wedge double gates are only the default options for a few of valve manufacturers.

Parallel double gates 
Compared with the other three kinds of gates, the biggest feature of parallel double gates is that this structure transfers the friction produced in the closing process to the non-sealing surface, which helps reduce the wear of the sealing surface, improve the sealing performance of the gate, and prolong the service life of the gate valve. However, this kind of structure of gates is the most complex among the four kinds and the sizes of the parallel double gates are relatively large, which make it impossible for gate valves with small sizes to adopt parallel double gates and make the production costs of gate valves with this gate structure increased by 20% to 30%. Therefore, parallel double gates are only default options for individual manufacturers.