Gate Valves are classified as follows
They are classified into several types based on their disc and stem types.
Types Based on Closing Element:
- Parallel disk Gate Valve: Parallel disc gate valves are composed of two discs that are moved apart against parallel seats by a spring at the point of closure. The knife gate valve is the most well-known form, with a flat gate between two parallel seats (an upstream and a downstream seat) to produce the requisite shut-off. A parallel gate valve’s applicability is limited to low pressures and pressure drops.
- Solid-Wedge Gate Valve: The solid, or single wedge gate valve, is the most common and least expensive type used in the process industry for oil, gas, and air services. The wedge shape’s goal is to introduce a large additional seating load. The Solid-Wedge Gate Valve can be installed in any position and is suitable for practically all fluids and turbulent flow services. In some cases, the valve cannot be closed until the system temperature reheats it; this is known as “thermal blinding.” Wedge gate valves are classified as either inside screws or outside screw patterns. Solid wedge gate valves are commonly used as sluice valves in the waterworks industry.
- Flexible Wedge Gate Valve: A flexible wedge gate valve is made up of a one-piece disc with a cut around the perimeter (the cut varies in size, shape, and depth). Thermal expansion and contraction cause no problems in such gate valves because the disc can compensate for this and remain easily open. To prevent thermal blinding, flexible wedge gate valves are commonly used in steam systems.
- Split Wedge Gate Valve: Split wedge gate valves are manufactured in two parts. This allows the wedge angle formed by their outer faces to suit the seat (self-adjusting and self-aligning to both seating surfaces).
- Double-disc Valves: The gate in these gate valves is made up of two discs that are driven apart against parallel seats by a spring. This ensures tight sealing without relying on fluid pressure, making this type of valve ideal for handling steam as well as gases and light oils.
- Bellows Seal Gate Valves: Bellows seal gate valves are designed to reduce exposure to hazardous substances caused by valve-stem leakage. The bellows are a metallic device that closes the gap between the stem of the valve and the bonnet to prevent system fluid from escaping into the atmosphere. They are composed of convolutions that may move linearly. During operation, these bellows eliminate the leak channel to the outside.
Types Based on Stem:
- Rising Stem Gate Valve with Outside Screw: This gate valve is also known as an OS & Y type (Outside steam and York). The stem rises when the valve is opened and lowers when it is closed, indicating the position of the gate valve. The stem threads are never in contact with the flow media (no corrosion or erosion).
- Non-Rising Stem Gate Valve: The stem of a non-rising stem gate valve, also known as an insider screw valve, is threaded into the gate. The hand wheel and stem move together, and the stem does not rise and fall. The flow medium is in line with the stem.
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