Gate valve: An on-off valve that works by inserting a rectangular gate or wedge into the flow of the fluid. The fugitive emission standard for gate valves is covered by API 624 and ISO 15848-1. It should be noted that the stem motion in a gate valve is typically linear, which creates a lot of friction between the valve stem and packing. This friction can cause packing wear and tear as well as leakage. Gate valves are available in different types, such as slab, expanding and wedge. Wedge gate valves have a sealing element in the shape of a wedge. A wedge gate valve is a torque seated valve, meaning that the wedge is expanded from both sides due to the stem force and provides sealing. The expansion of the valve closure member due to the stem axial force is called “wedging effect.” Expanding gate valves are also torque seated valves with a closure member in two sections, one male and the other female. Slab gate valves have a flat disk or closure member that provides sealing due to the fluid pressure. Slab gate valves, unlike expanding and wedge gate valves, are not torque seated..3.1 Height
Gate valves have more height than ball valves due to their high body and upward stem and gate movement for rising stem design. The height of a gate valve could be considered a disadvantage, since it can impose a manifold structure with higher height. Usage of a linear actuator on top of a TCG valve could make the height differential even greater compared to an actuated ball valve. One should bear in mind that rack and pinion or scotch and yoke actuators, which are used for ball valve automation, stand horizontally when the valve is connected to a horizontal pipe, whereas linear actuators stand vertically when the TCG valve is connected to horizontally installed piping. Fig. 4.33 illustrates the height of an actuated slab gate valve.
Gate valves or ball valves are two typical valves used in the manifolds. Gate valves have a long history of use in subsea blowout preventer (BOP) stacks, trees, and manifolds and are considered relatively reliable devices because both the valve and the valve actuators have been through extensive development with proven field use and design improvements. Figure 19-6 illustrates two types of subsea gate valves. Figure 19-6A shows a WOM(Worldwide Oilfield Machine, Inc.) subset gate valve with actuator, compensatory, and ROV bucket. The hydraulic actuator is designed with a fail-safe model and spring returns with the RIV. The mechanical RIV is for backup. Figure 19-6B shows a MOW subset gate valve with only an RIV bucket. Both valves are designed, built, and tested based on API 6A [6] and 17D [7], which can be used up to a water depth of 13,000 ft (4000 m).
Gate Valves
Gate valves work by inserting a rectangular gate or wedge into the path of a flowing fluid. They are operated by a threaded stem which connects the actuator (generally a hand wheel or motor) to the stem of the gate. If the valve has a rising stem its position can be seen just by looking at the position of the stem. Fig. 5.2 shows the internals of a Gate Valve that is half open.
Gate valves are used when a straight-line flow of fluid and minimum flow restriction are needed. Gate valves use a sliding plate within the valve body to stop, limit, or permit full flow of fluids through the valve. The gate is usually wedge-shaped. When the valve is wide open, the gate is fully drawn into the valve bonnet. This leaves the flow passage through the valve fully open with no flow restrictions. Therefore, there is little or no pressure drop or flow restriction through the valve.
Gate valves are not suitable for throttling volume. The control of flow is difficult because of the valve’s design and the flow of fluid slapping against a partially open gate can cause extensive damage to the valve. Except as specifically authorized by the manufacturer, gate valves should not be used for throttling.
Gate valves are classified as either rising-stem or non-rising-stem valves. The non-rising-stem valve is shown in Figure 7-2. The stem is threaded into the gate. As the hand wheel on the stem is rotated, the gate travels up or down the stem on the threads while the stem remains vertically stationary. This type of valve will almost always have a pointer indicator threaded onto the upper end of the s
A gate valve is generally used to completely shut off fluid flow or, in the fully open position, provide full flow in a pipeline. Thus it is used either in the fully closed or fully open positions. A gate valve consists of a valve body, seat and disc, a spindle, gland, and a wheel for operating the valve. The seat and the gate together perform the function of shutting off the flow of fluid.
ATEX and fire test requirements
Gate and globe valves can have fire test certificates according to API 6FA or ISO 10497 standards. The fire test certificate is not usually required for gate and globe valves with no nonmetallic parts. A fire test guarantees that the valve will function properly during a fire. is the European regulatory framework for manufacturing, installation, and use of equipment in explosive atmospheres. certification indicates that the valve does not have any source of ignition, which is applicable for equipment in potentially explosive atmospheres. Valves with actuators are usually in the scope of work because the directive does not consider the process source of ignition inside Only external s
ources of ignition such as actuators with electrical parts make the valve fall inside .
4.2.8.1.1 General considerations
Gate valves are characterized by a “gate” (Figures 4.49 and 4.50) that closes in a plane perpendicular to the flow of fluid. They are used primarily for on/off, non throttling service. Shearing of high-velocity flow will cause a partially open disk to vibrate and chatter, which will damage the seating surfaces and prevent a tight seal. They are suitable for most fluids including steam, water, oil, air, and gas. Gate valves may have either a solid or flexible wedge disk. In addition to on/off service, gate valves can be used for regulating flow, usually in sizes 6 in. and larger, but will chatter unless the disk is fully guided throughout trave
Gate valves are used to shut off the flow of liquids rather than for flow regulation, which is frequently done with a globe valve. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low flow resistance.[1] The size of the open flow path generally varies in a nonlinear manner as the gate is moved. This means that the flow rate does not change evenly with stem travel. Depending on the construction, a partially open gate can vibrate from the fluid flow.[1]
Gate valves are mostly used with larger pipe diameters (from 2″ to the largest pipelines) since they are less complex to construct than other types of valves in large sizes.
At high pressures, friction can become a problem. As the gate is pushed against its guiding rail by the pressure of the medium, it becomes harder to operate the valve. Large gate valves are sometimes fitted with a bypass controlled by a smaller valve to be able to reduce the pressure before operating the gate valve itself.
Gate valves without an extra sealing ring on the gate or the seat are used in applications where minor leaking of the valve is not an issue, such as heating circuits or sewer pipes.
Common gate valves are actuated by a threaded stem that connects the actuator (e.g. hand wheel or motor) to the gate. They are characterized as having either a rising or a non rising stem, depending on which end of the stem is threaded. Rising stems are fixed to the gate and rise and lower together as the valve is operated, providing a visual indication of valve position. The actuator is attached to a nut that is rotated around the threaded stem to move it. Non rising stem valves are fixed to, and rotate with, the actuator, and are threaded into the gate. They may have a pointer threaded onto the stem to indicate valve position, since the gate’s motion is concealed inside the valve. Non rising stems are used where vertical space is limited.
Gate valves may have flanges ends drilled according to pipeline-compatible flange dimensional standards.
Gate valves are typically constructed from cast iron, cast carbon steel, ductile iron, gunmetal, stainless steel, alloy steels, and forged steels.
All-metal gate valves are used in ultra-high vacuum chambers to isolate regions of the chamber.[2]
Bonnet
Bonnets provide leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. A screw-in bonnet is the simplest, offering a durable, pressure-tight seal. A union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. A bolted bonnet is used for larger valves and higher pressure applications.[3]
Pressure seal bonnet
Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 2250 psi . The unique feature of the pressure seal bonnet is that the bonnet ends in a downward-facing cup that fits inside the body of the valve. As the internal pressure in the valve increases, the sides of the cup are forced outward. improving the body-bonnet seal. Other constructions where the seal is provided by external clamping pressure tend to create leaks in the body-bonnet joint.
Knife gate valve
For plastic solids and high-viscosity scurries such as paper pulp, a specialty valve known as a knife gate valve is used to cut through the material to stop the flow. A knife gate valve is usually not wedge shaped and has a tapered knife-like edge on its lower surface
ate valves are used to shut off the flow of fluid by inserting a rectangular gate or wedge into the path of a flowing fluid. Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened enabling gate valves to offer straightway flow with very little pressure drop. Gate valves are mostly used with larger pipe diameters (from 2″ to the largest pipelines) since they are less complex to construct than other types of valves in large sizes. More recently, however, the larger sizes have been supplemented by butterfly valves due to space limitations under which they are installed.
The gate valve, as illustrated in on the right, generally consists of a gate-like disc, actuated by a screwed stem and hand-wheel which moves up and down at right angles to the flow. In the closed position, the disc seats against two faces to shut off flow. To retain the fluid in the pipeline, a gland is provided which is supplied with some type of packing to resist leakage.
Gate valves consist of three major components: body, bonnet, and trim. The body is generally connected to the piping by means of flanges, screwed, or welded connections. The bonnet, containing the moving parts, is joined to the body, generally with bolts, to permit cleaning and maintenance. The valve trim consists of the stem, the gate, the wedge, or disc, and the seat rings.
The main operation mechanism is very simple. When the hand-wheel is turned, it rotates the stem, which is translated into the vertical movement of a gate via threads. They are considered multi-turn valves as it takes more than one 360° turn to fully open/close the valve. When the gate is lifted from the path of the flow, the valve opens and when it returns to its closed position, it seals the bore resulting in a full closure of the valve.