Gate Valves

We offer a full range of gate valves in a variety of types, sizes, pressure ratings and materials, with wafer type, screwed, welded or flanged connections. Gate valves are available from small to very large sizes.

Gate valves are so-named because the part that either stops or allows flow through the valve acts like a gate. The valve opens by lifting a round or rectangular wedge out of the path of the flow. Gate valves are designed to be fully opened or closed and are therefore not suitable for throttling purposes. When fully open, the typical gate valve has little or no obstruction in the flow path, resulting in very low pressure drop, and they are often suitable for hot tapping and pigging.

Gate valves are generally designed for use with the flow of liquids and gases but there are variations to cope with specific requirements. For example, one problem with wedge gate valves in steam service is that when the valve is closed and steam is brought into the system, the metal wedge expands and can get stuck, making opening the valve difficult or impossible.

Parallel slide valves are designed for use with steam, or other fluids at high temperature. A spring is fitted between the valve discs to keep them in contact with the body seat and thus allow expansion. In addition, the sliding action of the valve discs across the body seat during operation assists in removing any foreign matter such as scale that may have accumulated on the respective faces. In the closed position, positive shut off is achieved by the inlet pressure forcing the downstream disc firmly onto its respective seat. The maximum closing force therefore occurs when the isolated downstream section of the pipework is completely exhausted of pressure, i.e. when there is maximum differential pressure across the valve body. This pressure differential would typically need to be 3 or 4 bar to give satisfactory shut off.

Knife-gate valves are used when sediment may block a normal wedge gate. The gate is a narrow plate with a shaped edge to cut through solids. They are ideal for applications with a high suspension of solids or fibrous content such as powders, slurry, ash and pulp. Care should be taken when specifying knife gate valves to state whether flow is uni- or bi-directional.

Resilient seated gate valves incorporate a soft seat in the wedge to give a tighter shut off; some valves have an elastomer coated wedge to achieve this. These valves are particularly suited to gas service, provided the materials are chosen carefully.

Wedge gate valves, particularly in larger sizes, are difficult and expensive to actuate for remote operation, requiring a rotary motion to lift the gate, but parallel slides, with a lower gate mass offer less of a challenge. Knife gates can easily be pneumatically actuated, being a linear movement.

When selecting a gate valve, it is important to consider operating temperature and pressure, media properties, duty requirements, physical limitations and suitability for the environment.

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