Gate valves are mainly designed to start or stop the flow, and when a straight-line flow of fluid and minimum flow restriction are needed. In service, these valves generally are either fully open or fully closed. The gate valve’s disk is completely removed when the valve is fully open; the disk is fully drawn up into the valve bonnet. This creates an opening for flow through the valve at the same inside diameter as the pipe system in which the valve is installed. A gate valve can be used for a wide range of liquids and provides a tight seal when closed.
There are three main parts in a gate valve – body, bonnet, and trim. The body is generally connected to other equipment by means of flanged, screwed or welded connections. The bonnet, which contains the moving parts, is attached to the body, usually with bolts, to permit maintenance. The valve trim comprises of the stem, the gate, the disc or wedge, and the seat rings.
Gate valves are available with different disks or wedges. Ranging from the gate valves are usually made by the type of wedge used. The most commonly available one is –
Solid wedge, which is the most commonly used disk and vale with this type of wedge can be installed in each position and it is suitable for almost all liquids.
A flexible wedge which is a one-piece disc with a cut around the perimeter to improve the ability to correct mistakes or changes in the angle between the seats.
The split wedge is self-adjusting and self-aligning to both seat sides. This wedge type consists of two-piece construction which seats between the tapered seats in the valve body. This wedge type is suitable for the treatment of non-condensing gases and liquids at normal temperatures, particularly corrosive liquids.
The seats for the gate valves are either provided integrally with the valve body or in a seat ring type of construction. Seat ring construction provides seats that are either threaded into position or are pressed into position and seal welded to the valve body. The latter form of construction is recommended for higher temperature service.
Integral seats provide a seat of the same material of construction as the valve body while the pressed-in or threaded-in seats permit variation. Rings with hard facings may be supplied for the application where they are required.