Gate Valve

Gate valves are on-off valves and are designed for the primary function

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23 May 2014 /  /  in Gate Valve Technical Article

Gate valves feature a sliding partition that can be closed to block flow or opened fully for maximum flow. Gate valves are used to isolate sections of pipelines, branch off-takes and pieces of equipment. They are on-off valves designed for the primary function of flow isolation and should only be operated in the fully closed or fully open positions. The sliding motion of the gate is effected by a rotating screw, known as a spindle or stem.

Sluice valves are gate valves and prior to the introduction of fusion bonded coatings they were of a heavier construction to endure buried service applications, whereas gate valves were associated with above ground applications. Today's modern coating systems remove the need for distinction between buried and above ground applications and therefore no need for sluice valve and gate valve distinction.

There is a growing industry trend to use gate valves in flow regulating and scour applications. When gate valves are used in these applications it is essential that they are operated in thefully opened position and any regulation of flow controlled by other means, such as orifice plates.

Gate valves should not be used for throttling or adjusting flow as associated turbulence and high velocity can lead to vibration, chattering and fretting wear, as well as cavitation damage of the valve and downstream pipeline.

There are two design options for Gate Valves, Metal Seated and Resilient Seated. These two options can also be split into two categories Non- Rising Spindle (Inside Screw) and Rising Spindle (Outside Screw).

Metal seated gate valves comprise a metal gate, typically wedge shaped and made of gunmetal for valves up to and including 200mm and ductile iron with gunmetal sealing rings for larger sizes. The gate and body are fitted with metal sealing rings by threading or plastic deformation to prevent loosening in service. A continuous seal is provided behind the rings to prevent corrosion.

The valve is closed by appropriate rotation of the spindle which drives the gate down between the sealing rings. Sealing is effected by the mating of the sealing rings. Sometimes the sealing surfaces can become damaged from the impact of foreign debris or from foreign debris being lodged between the sealing faces. Throttling of a metal seated gate valve is the most commoncause of damage to the sealing faces. Repair of the sealing surfaces is not a simple operation and a factory refit is normally necessary.