API 600, API6D & API 602
A gate valve can be defined as a type of valve that used a gate or wedge type disk and the disk moves perpendicular to flow to start or stop the fluid flow in piping. A gate valve is the most common type of valve that used in any process plant. It is a linear motion valve used to start or stop fluid flow. In service, these valves are either in fully open or fully closed position. When the gate valve is fully open, the disk of a gate valve is completely removed from the flow. Therefore virtually no resistance to flow. Due to this very little pressure drops when fluid passes through a gate valve.
To achieve proper sealing, when the valve is fully closed, 360° surface contact is required between disk and seats. Gate valves should not be used for regulation or throttling of flow because accurate control is not possible. The high velocity of the flow in the partially open valve may cause erosion of the disc and seating surfaces and also creates vibration and noise.
Gate valves tend to be slightly cheaper than ball valves of the same size and quality. They are generally slower in actuation than quarter-turn valves and are most commonly used in applications where valve operation is infrequent such as isolating valves. Gate valves are primarily designed for fully open and fully closed service functions and are not typically used as control or regulating valves. Although electrically actuated gate valves exist, the infrequent functioning of these valves make manual actuation a cost-effective option.
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Solid wedge is most common & widely used disk types because of its simplicity and strength. A valve with solid wedge may be installed in any position, and it is suitable for almost all fluids. It can be used in turbulent flow also. However, it does not compensate for changes in seat alignment due to pipe loads or thermal expansion. So, this type of disk design is most susceptible to leakage. Solid wedge is subjected to thermal locking if used in high-temperature service.
The flexible wedge is a one-piece solid disk with a cut around the perimeter. These cuts vary in size, shape, and depth. A shallow, narrow cut on wedge perimeter gives less flexibility but retains strength. A cast-in recess or deeper and wider cut on wedge perimeter gives more flexibility but compromises the strength. This design improves seat alignment and offers better leak tightness. It also improved performance in situations where thermal binding possible. Flexible wedges Gate valves are used in steam systems.