Types of Gate Valves

Posted: 05/08/2019 02:05:43   Hits: 15
A gate valve can be defined as a type of valve that used a gate or a wedge type disk, and the disk moves perpendicular to the fluid in the pipeline to shut off the fluid. The valve is either in fully open or fully closed position. When a gate valve is fully open, the disk of the gate valve is completely removed from the flow. Due to very little pressure drops, when the fluid passes through a gate valve, there is no resistance to flow virtually. To achieve proper sealing, when the valve is fully closed, 360° surface contact is required among the disk and seats. Gate valves should not be used for regulation or throttling of flow because they cannot accurately control the flow. The high velocity of the flow in the partially open valve may cause erosion of the disc and seating surfaces, as well as vibration and noise.

According to the disk types, gate valves can be classified into solid wedge gate valves, flexible wedge gate valves, and valves with a split wedge or parallel disks.

Solid Wedge Gate Valves

Solid wedge is the most common and widely used disk type because of its simplicity and strength. A valve with a solid wedge can be installed in any position, and it is suitable for almost all fluids. It can be used in turbulent flow as well. 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. A solid wedge is subjected to thermal locking if used in high-temperature situations. Thermal locking is a phenomenon in which the wedge is stuck between the seats due to the expansion of the metal. Solid-wedge gate valves are generally used in low and medium pressure and temperature applications.

Flexible Wedge Gate Valves

A 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 gives less flexibility but retains strength. A cast-in recess or deeper and wider cut on wedge gives more flexibility but compromises the strength. This design improves seat alignment and offers better sealing performance. Flexible wedges gate valves are used in steam systems. Thermal expansion of steam line sometime causes distortion of valve bodies. The flexible gate valve allows the gate to flex as the valve seat compresses due to thermal expansion of steam pipeline. The disadvantage of flexible gate valve is that the fluid in the pipeline tends to remain in the disk. These may result in corrosion and ultimately weakening the disk.

Gate Valves with a Split Wedge or Parallel Disks

A split wedge disk consists of two solid pieces that hold together with the help of a special mechanism. The split disk can be in a wedge shape or a parallel disk type. Parallel disks are spring loaded, so they are always in contact with seats and give bi-directional sealing. A split wedge is suitable for handling noncondensing gasses and liquids at normal and high temperature.

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