A gate valve, also known as a sluice valve, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar, so gate valves are often used when a straight-line flow of fluid and minimum restriction is desired.
Gate valves are primarily designed to start or stop 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 disc of a Gate valve is completely removed when the valve is fully open; the disk is fully drawn up into the valve Bonnet. This leaves an opening for flow through the valve at the same inside diameter as the pipesystem 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.
On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that flow rate does not change evenly with stem travel. Also, a partially open gate disc tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing disk and seat wear and eventual leakage if used to regulate flow. Typical gate valves are designed to be fully opened or closed.When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.
Construction of a Gate valve
Gate valves consists of three main parts: body, bonnet, and trim. The body is generally connected to other equipment by means of flanged, screwed or welded connections. The bonnet, which containing the moving parts, is attached to the body, usually with bolts, to permit maintenance. The valve trim consists of the stem, the gate, the disc or wedge and the seat rings.
Types of a Gate valve
The gate valves are normally classified as wedge gate valves (generally called cast steel gate valves), knife gate valves and slab gate valves and forged steel gate valves.
The gate valves can be classified as API 6D gate valves, API 600 gate valves and API 602 gate valves.
Discs of a Gate valve
Gate valves are available with different discs or wedges. Ranging of the Gate valves (made by China gate valve supplier) is usually made by the type of wedge used. The gate faces can form a wedge shape or they can be parallel.
The most common were:
- Solid wedge is the most commonly used disk by its simplicity and strength.
A valve with this type of wedge can be installed in each position and it is suitable for almost all liquids. The solid wedge is a single-piece solid construction, and is practically for turbulent flow.
- Flexible wedge 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 reduction will vary in size, shape and depth. A shallow, narrow cut gives little flexibility but retains strength.
A deeper and wider cut, or cast-in recess, leaves little material in the middle, which allows more flexibility, but compromises strength.
- Split wedge is self-adjusting and selfaligning to both seats sides. This wedge type consists of two-piece construction which seats between the tapered seats in the valve body. This type of wedge is suitable for the treatment of non-condensing gases and liquids at normal temperatures, particularly corrosive liquids.
Most common wedges in Gate valves
Stem of a Gate valve
The stem, which connects the handwheel and disk with each other, is responsible for the proper positioning of the disc. Stems are usually forged, and connected to the disc by threaded or other techniques. To prevent leakage, in the area of the seal, a fine surface finish of the stem is necessary.
Gate valves are classified as either:
- Rising Stem
- Non Rising Stem
For a valve of the Rising Stem type, the stem will rise above the handwheel if the valve is opened. This happens, because the stem is threaded and mated with the bushing threads of a Yoke. A Yoke is an integral part from a Rising Stem valve and is mounted to the Bonnet.
For a valve of the non Rising Stem type, there is no upward stem movement if the valve is opened. The stem is threaded into the disk. As the handwheel on the stem is rotated, the disk travels up or down the stem on the threads while the stem remains vertically stationary.
In the main Menu “Valves” you will find links to detailed (large) drawings of both stem types.
Seats of a Gate valve
Seats for Gate valves are either provided integral with the valve body or in a seat ring type of construction. Seat ring construction provides seats which 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.
Advantages and disadvantages of Gate valves
- Good shutoff features
- Gate valves are bidirectional and therefore they can be used in two directions
- Pressure loss through the valve is minimal
- They can not be quickly opened or closed
- Gate valves are not suitable for regulate or throttle flow
- They are sensitive to vibration in the open state
By Kevein from Zhejiang Relia Valve Co., Ltd. professional China valve supplier, China wafer check valve and China metal seated ball valve supplier