What Is a Gate Valve?
A gate valve is a mechanism designed to control the flow of fluids, like liquids or gases, using a disc (valve disc) to shut off the flow. In the JIS B0100 Glossary of Terms for valves, a gate valve is defined as a valve where the plug moves vertically, dividing the fluid flow path and aligning it in a straight line for opening or closing.
The term ‘gate valve’ is derived from the way the disc slides into the flow channel, resembling a gate in a sluice gate.
Applications of Gate Valves
Examples of Gate Valves in Use
Gate valves manage fluid flow across various pressure and temperature ranges. They are used in domestic, industrial, and academic settings. Common applications include water meters, gas meters, and water heater pipework.
Typically, gate valves are used either fully open or fully closed, as partial opening can cause disc vibration. They function effectively as stop valves for shut-off purposes.
They are often installed as shut-off valves in pipelines or as dividing valves in water supply systems. Manual gate valves require extensive handle turning and time to operate. Hence, automatic actuator-equipped gate valves are preferred for frequent or remote operations.
Principle of Gate Valves
Gate Valve Open/Close Condition and Fluid Flow
The operation of a gate valve is straightforward. In the open state, the disc lowers, closing the flow path. Conversely, when closed, the disc rises, allowing fluid flow. This movement is controlled by a screw mechanism in the stem, operated by a handle or actuator.
1. Pressure Drop in Gate Valves
Gate valves, often full-port, exhibit minimal pressure drop when fully open. The straight flow path and uniform cross-sectional area reduce turbulence and friction losses, unlike globe valves which have higher pressure loss due to their S-shaped path.
2. Water Hammer Phenomenon in Gate Valves
Gate valves are less susceptible to water hammer due to their gradual opening and closing. Water hammer, a sudden pressure change in pipes, is mitigated by the gate valve’s design.
Pressure Fluctuations Due to Water Hammer Can Cause the Following Problems
Sudden pressure increases can damage pipes, pumps, valves, and support hardware. Conversely, pressure drops can deform pipes and cause secondary pressure spikes. These fluctuations also complicate pressure control.
Gate Valve Structure
Gate Valve Structure
Gate valves consist of a body (valve box), disc (valve plug), stem (valve stem), and handle or actuator. The handle, attached to the stem, rotates to control the disc’s vertical movement.
Types of Gate Valves
1. Classification According to Operating Method
Gate Valve Operating Systems
Gate valves have three main operating types:
Manual Type: Operated by handle rotation.
Air-Actuated Type: Operated by a pneumatic actuator.
Electric Type: Operated by an electric actuator.
2. Classification According to Disc Shape and Construction
Discs can be parallel or wedge-shaped. Parallel sliding uses two parallel discs, and double-disc types use two discs pushed apart by the stem.
3. Stem Lift Type and Non-stem Lift Type
Stem lift types indicate open/close status visually, while non-rising types do not show visible changes in the stem or handle position.
4. Classification According to Body Material
Materials include grey cast iron, spheroidal graphite cast iron, carbon steel, high-temperature steel, stainless steel, copper, and copper alloy. Selection depends on fluid type, pressure, temperature, flow velocity, impurities, corrosion resistance, and applicable standards.