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What is a gate valve?

Gate valve housing cylinder in machining fixture
A gate valve is a valve that permits or restricts the flow of a liquid via a wedge or ‘gate’ that can be lifted out of or dropped into the path of the fluid. An important feature of a gate valve is the planar sealing surface between the gate and seats, making it the valve of choice when the fluid flows in a straight line, with little or no restrictions. In addition, since the gate or wedge is of the same size as the diameter of the pipeline, these valves are full bore, i.e., there is no obstruction to the fluid flow, and therefore no loss due to friction.

Gate valves are most commonly used in on/off applications, and not to regulate flow.

Vacuum gate valves are mainly used to control gas flow into a chamber, to isolate vacuum volumes from pumps, to sample entry locks from HV or UHV work chambers, and to enable transfer of objects between vacuum volumes. They are therefore most commonly used in ion implantation systems, OMBD systems and e-beam evaporation systems for high vacuum applications such as semiconductor fabrication. They are also used in metal finishing processes, and in the aeronautical industry, to develop anti-corrosion coatings.

Manufactured components of a gate valve

The main components of a gate valve assembly are the actuator and the body.

The Actuator is the part responsible for opening or closing the valve, and moves the valve gate in response to a signal (pneumatic or hydraulic actuators) or via manual manipulation (hand wheel).

The valve Body is a vacuum tight chamber that is part of a larger vacuum vessel or system, and holds all the operating parts of the valve —the disk, the seat, the stem and sleeves required to guide the stem — collectively known as the valve’s ‘trim.’ It is also the part of the valve that connects to the pipe carrying the fluid or gas the gate valve is controlling. Valve bodies are cast or forged in a variety of shapes; each part has a specific function and is therefore made of the metal or alloy suitable for that function and circumstance.

The Bonnet functions as the covering for the opening of the valve body, while also supporting the internal parts such as the stem, disk, and actuator. The bonnet is usually made of the same material as the body, and is threaded, bolted or welded to the body. While screw-in bonnets are the simplest, bolted bonnets are used for larger valves and higher pressure applications.

The Gate, which consists of the disk/wedge and the seat, is the part that actually blocks or opens the pipeline or the valve’s body port. Gate faces are usually either parallel or wedge shaped. A parallel gate is a flat disk between two parallel seats, upstream and downstream, and is used when tight shutoff is not an important prerequisite. Wedge-shaped gate valves use two inclined seats and a slightly mismatched inclined gate, enabling tight shut-off. Gate disks or wedges are typically forged, and sometimes hard surfaced to provide good wear properties.

The seat or seal ring provides the seating surface for the disk. Gate valves usually have two seats, on both the upstream and downstream side; the disk in turn has two seating surfaces. When the disk is lowered, the seating surfaces of the disk come into contact with the valve seats to create a tight seal that stops the flow. The surfaces are often hard-faced by means of welding, and the contact surface is then machined, to improve the wear-resistance of the seal ring.

AmTech International provides a variety of vacuum gate valve parts including sealing plates, the operating plates, flanges, bonnets, cylinders, rods, and housing assemblies. Contact AmTech today for gate valve parts that are competitively priced, while offering exceptional quality and durability.