May. 06, 2024
gate valves, or sluice valves, are mainly used to block or permit fluid flow through pipes. They are not good at regulating flow for which other valve designs, such as globe valves, are better suited. Ball valves are another on/off valve type unsuited to throttling. Gate valves offer a size advantage over these other types in terms of how much space must be allotted between pipe flanges to accommodate the valve.
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Gate valves consist of three major portions, the valve body and seats, the gate (or disc) and stem, and the packing and bonnet. In operation, the body and seats remain stationary while the threaded stem rotates to lift the gate off its seats. Stem rotation is accomplished manually through a handwheel or automatically via a valve actuator. The bonnet houses the disc while the valve is open and provides a location for the stem packing where the stem exits the valve.
As with some other valve types, a distinction is made between rising stem and non-rising stem designs. Rising stem styles give a quick visual indication as to whether the valve is opened or closed. In non-rising stem designs, the stem threads into the disc, raising or lowering it as the stem turns while remaining fixed axially. Gates can be straight-sided or tapered discs. Wedge gate valves, also called tapered gates, are most common as they provide stronger sealing action and they can be solid, flexible, or split. Flexible gates accommodate some distortion of the seats arising from pipeline flex.
When a gate valve is fully opened, the gate disc is completely withdrawn from the flow path into the bonnet. For this reason, the pressure drop through gate valves is minimal. When closed, the gate disc seals against seats in the valve body which may be integrally cast or, more likely, welded or threaded into place. Metal seats are most common and seats are generally lapped after installation. In certain applications, the seats may be hardened. Seats on both sides of the gate permit the valve to be used bi-directionally. Where some leakage is acceptable, the gate seals without an extra sealing ring.
Gate valves should not be used in other than fully opened or fully closed positions as partially opened gates can expose the valve internals to accelerated and uneven wear and vibration. Another problem with using a gate valve in regulating service is the gate does not open the valve passage uniformly, making it difficult to produce a consistent increase in flow for a given turn of the stem.
Gate valves are not quarter-turn devices such as ball valves but instead close slowly through multiple revolutions of their handwheels. This can be a benefit in the prevention of water hammer. Acme threads are commonly employed on the stems, with multi-lead threads sometimes used for faster operation. The unthreaded portion of the stem is usually finished to provide a good sealing surface for the packing. Packing is adjusted by tightening a gland nut or nuts, though some designs use springs – so-called live loading – to provide constant pressure on the seal for better reduction of fugitive emissions.
Gate valves are used in wastewater plants, power plants, and process plants for shut-off and isolation service. They overshadow ball valves in larger applications because of the mechanical advantage a threaded stem offers over a quarter-turn lever. Some very large valves must incorporate a means of pressure reduction before the gate can be moved. Their simple design makes them an economical solution as pipe diameters increase beyond 2 inches.
Material selection for gate valve bodies runs the gamut, with cast iron and steel common for larger valves and stainless steel, forged steel, bronze, etc. widely available in smaller sizes. Non-metallic options such as plastic gate valves are also available. Specifying material for the body generally includes all components under pressure, while “trim” refers to the components apart from the body, including the seats, the disc, the stem, and, if applicable, the bellows. Larger sizes are identified by an ASME class pressure rating and ordered with standard bolted or welded flanges. Sizing a gate valve is straightforward as the design precludes any significant pressure drop through the valve.
Non-rising stem designs are popular where vertical space is limited – aboard ships, for example. Rising stem designs offer a fast, visual confirmation of a valve’s status, though the exposed stem can be subject to corrosion. Non-rising stem valves often use an indicator to verify the gate position. Neither design has much impact on the performance of the actual valve.
Gate valves are routinely automated using electrical rotary actuators, and their operation can be sped up with the use of hydraulic or pneumatic linear actuators. The effort required to open and close large gate valves manually can be reduced through the use of geared actuators.
Some building codes require that on/off valves be installed upstream of certain equipment, on water heater inlets, for example. Here, a ball or gate valve is acceptable while a globe valve is not. At one time, gate valves were predominant in residential plumbing systems, where they had a tendency to “freeze” open from disuse. New plumbing systems mostly use lever-actuated ball valves in their place, as the ball has a much lower tendency to stick. The additional space required for the lever can require some creativity in retrofits.
A special gate valve known as a knife gate valve is used to control the movement of slurries and viscous liquids. Sliding gate valves are used for dispensing dry and bulk materials from hoppers.
A gate valve makes economic sense when compared to other valve types intended for the same purpose. They provide positive shutoff, low pressure loss, and bi-directionality in a compact envelope. Their downsides include slow actuation, an inability to regulate flow, and susceptibility to vibration.
This article presented a brief discussion of gate valves including the different types and applications. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products. More information on valves, in general, can be found at the Valve Manufacturers Association website, www.vma.org.
The gate valve, abbreviated as GV, is one of the most frequently used valve in piping systems and is classified as either "rising-stem" or "nonrising-stem" valves. The rising-stem gate valve has the stem attached to the gate, both gate and stem rise and lower together as the valve handwheel or actuator turns the stem. In the nonrising-stem gate valves the stem is threaded into the wedge, rising and lowering the wedge.
It is a multi turn valve which should be used for on and off service. If the valve is partially open as an attempt to throttle or control flow, turbulence from the stream could cause the wedge to vibrate and create a chattering noise. When fully opened, the gate valve creates minimal obstruction to the flow.
Gate valves control the process through the pipe with a gate. The gate might be wedge shaped or knife shaped, that slides up or down as the valve's handwheel is turned. As the handwheel is rotated, the gate slides through the valve body to block or release the flow.
Face to face dimensions for full and standard port valves is the same. All ball valves 2" and below are both standard and full port valves.
Gate 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 flanged, 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.
The closing member, sometimes referred as gate also, comes in a variety of designs and technologies to produce effective sealing for differing applications. There are usually two types of gate valve closing members which are having further varieties.
Parallel gate valves have a parallel faced gate like closing member. This closing member may consists of a single disc or twin discs with a spreading mechanism in between. The force that presses the disc against the seat is controlled by the fluid pressure acting on either a floating disc or a floating seat. Because the disc slides across the seat face, parallel gate valves are also capable of handling fluids, which carry solids in suspension.
Conventional Parallel Gate Valve
In a conventional parallel slide gate valve the closure member consists of two discs with springs in between. The duties of these springs are to keep the upstream and downstream seating’s in sliding contact and to improve the seating load at low fluid pressures. The discs are carried in a belt eye in a manner that prevents their unrestrained spreading as they move into the fully open valve position.
The advantages offered by this construction include not only economy of construction but also a reduced operating effort and lower maintenance cost. The only disadvantage is a slight increase in pressure loss across the valve.
Through-Conduit Gate Valve
Through-conduit gate valves are one-unit gates that include a bore size hole as shown in figure on the right. In open state, the bore size hole is aligned with the two seat rings to create a smooth flow with minimal turbulence. This special design allows for minimal pressure loss on the system and is perfect for transportation of crude oil and natural gas liquids (NGLs). The valve seats remain clean, however, the disc cavity can capture foreign material. Therefore, the cavity typically has a built-in plug for maintenance purposes of draining the accumulated foreign material.
These valves are used in pipelines where pigs are run through the piping to perform cleaning of built-up deposits or debris. The typical applications of conduit valves include dirty river water with suspended solids or water with sludge or debris.
Knife Gate Valve
Knife Gate Valves are a specific type of parallel gate valve and is designed to handle systems with high content of suspended solids. The knife gate valves are especially beneficial for handling slurry, viscous, corrosive and abrasive media. The valve owes its ability to handle these fluids to the knife-edged disc, which is capable of cutting through fibrous material, and the virtual absence of a valve body cavity. The disc travels in lateral guides and is forced against the seat by lugs at the bottom. If a high degree of fluid tightness is required, the valve may also be provided with an O-ring seat seal.
The valves find application in paper and pulp, minerals and metals, steel plants, thermal power plants and chemical/ petrochemical industries. Knife gate valve has a short face-to-face length compared to other gate valves. As a consequence a knife gate valve is light weighted compared to other gate valves.
Wedge gate valves differ from parallel gate valves in that the closure member is wedge-shaped instead of parallel. The purpose of the wedge shape is to introduce a high supplementary seating load that enables wedge gate valves to seal not only against high, but also low, fluid pressures. The degree of seat tightness that can be achieved with wedge gate valves is therefore potentially higher than with conventional parallel gate valves.
Efforts to improve the performance of wedge gate valves led to the development of a variety of wedge designs; the most common ones are described in the following section.
Solid or Plain Wedge Gate Valve
Solid or plain wedge is most common & widely used disk types because of its simplicity and strength. It can be of solid or hollow construction. This design has the advantage of being simple and robust, but distortions of the valve body due to thermal and pipeline stresses may unseat or jam the metal seated wedge making it more susceptible to leakage. A valve with solid wedge may be installed in any position, and it is suitable for almost all fluids. It can be used in turbulent flow also. Solid wedge is subjected to thermal locking if used in high-temperature service.
Thermal locking is a phenomenon in which wedge is stuck between the seats due to the expansion of the metal. Solid-wedge gate valves are generally used in moderate to lower pressure-temperature applications.
Efforts to overcome the alignment problem of plain wedges led to the development of self-aligning or split wedges. This permits the wedged gate to adapt itself to small amounts of distortion caused by pipeline strain or seat wear.
Split Wedge Gate Valve
Split wedge disk consists of two solid pieces and holds together with the help of special mechanism like a spacer ring or spring. To keep the plates together, the body has grooves in which the wedge assembly travels.Split wedge is self-adjusting and self aligning to both seats sides. Disk flexibility is inherent to the split wedge design. This flexibility allows the split wedge to seal more easily and it reduces stickiness between the sealing surfaces in cases where the valve seats are angularly misaligned. The mismatched angle is also designed with some free movement to allow the seating surfaces to match with each other.
This type of wedge is suitable for the treatment of non-condensing gases and liquids at normal temperatures, particularly corrosive liquids.
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Suggested reading:Flexible Wedge Gate Valve
The flexible wedge is a one-piece solid disk with a cut around the perimeter or with an integral boss in between. The wedge is sufficiently flexible to find its own orientation. Because the wedge is simple and contains no separate components that could rattle loose in service, this construction has become a favored design. This design improves seat alignment and offers better leak tightness. It also improved performance in situations where thermal binding possible.
The cut or integral boss 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.
The disadvantage of split gates is that process fluid tends to collect in between the disks. These may result in corrosion and ultimately weaken the disk.
The stem, which connects the hand-wheel and disk with each other, is responsible for the proper positioning of the disk. Stems are usually forged, and connected to the disk by threaded or other techniques. Depending on which end of the stem is threaded, stems can be rising or non-rising.
Rising stems are fixed to the gate and they rise and lower together as the valve is operated, providing a visual indication of the valve position and making it possible to grease the stem. A nut rotates around the threaded stem and moves it. This type of valve has an inside screwed stem and the packing is subjected to wear because of the up and down movement and turning motion of the stem. This type is only suitable for above-ground installation.
Non-rising stems are threaded into the gate, and rotate with the wedge rising and lowering inside the valve. Rotation of the wheel operates the valve, but the stem does not come out of the housing. They take up less vertical space since the stem is kept within the valve body. Non-rising valves are almost always fitted with a local visual pointer which indicates the position of the valve. Gate valves with non-rising stems are suitable for both above-ground and underground installations.
A metal seated gate valve has a depression in the valve bottom. The conical wedge fits into the depression in the valve bottom to ensure a tight closure. Herewith, sand and pebbles are embedded in the bore. The pipe system will never be completely free from impurities regardless of how thoroughly the pipe is flushed upon installation or repair. Thus any metal wedge will eventually lose its ability to be drop-tight.
A resilient seated gate valve has a plain valve bottom allowing free passage for sand and pebbles in the valve. If impurities pass as the valve closes, the rubber surface will close around the impurities while the valve is closed. A high-quality rubber compound absorbs the impurities as the valve closes, and the impurities will be flushed away when the valve is opened again. The rubber surface will regain its original shape securing a drop-tight sealing.
Gate valves meet the majority of valve requirements in process piping and are considered one of the most used valves of all the valves employed in refineries, petrochemical, and gas processing plants where pressure remains relatively low, but temperature may be very high. They are suitable for most fluids including steam, water, oil, air, and gas.
Gate valves are designed for fully open or fully closed service. They are installed in pipelines as isolating valves, and should not be used as flow control or regulating valves. When operating the valve stem, the gate moves up- or downwards on the threaded part of the stem.
Gate valves are often used when minimum pressure loss and a free bore is needed. When fully open, a typical gate valve has no obstruction in the flow path resulting in a very low pressure loss, and this design makes it possible to use a pipe-cleaning pig. A gate valve is a multiturn valve meaning that the operation of the valve is done by means of a threaded stem. As the valve has to turn multiple times to go from open to closed position, the slow operation also prevents water hammer effects.
Gate valves should not be used for regulation or throttling of flow because,
At high pressures, friction can become a problem. The seating load of the larger gate valves (except those with floating seats) can become so high at high fluid pressures that friction between the seating’s can make it difficult to raise the disc from the closed position. Such large gate valves are therefore frequently provided with a valved bypass line, which is used to relieve the seating load prior to opening the valve.
By-pass valves are generally used for three basic reasons:
Sometimes during the operation of gate valves, thermal expansion of a liquid trapped in the closed valve chamber will force the upstream and downstream discs into more intimate contact with their seats, and cause the pressure in the valve chamber to rise. The higher seating stress makes it in turn more difficult to raise the discs, and the pressure in the valve chamber may quickly become high enough to cause a bonnet flange joint to leak or the valve body to deform. Thus, if gate valves are used to handle a liquid with high thermal expansion, they must have a pressure-equalizing connection that connects the valve chamber with the upstream piping. The pressure-equalizing connection may be provided by a hole in the upstream disc or by other internal or external means.
Choosing the right gate valve goes beyond a simple catalog browse-and-pick. It demands an in-depth understanding of the technical factors that can drive your project toward success or failure. If the myriad of options is overwhelming, you can always seek guidance from AlterValve, the leading gate valve supplier.
This article aims to guide you, focusing mainly on gate valves' technical specifications, their operational efficiency, and cost-effectiveness. We will analyse the design of the wedge and the quality of natural rubber used in gate valves and how these factors influence your choice. So, prepare yourself to make an informed decision through this detailed examination.
Exploring the world of gate valves offers insights into their functionality and efficiency. It also provides information about their cost-effectiveness, a critical factor in choosing the right gate valve for specific applications. Let's proceed.
Gate valves, often known as water gate valves or sluice valves, emerge as a top pick for linear valves in pipelines. Their unique design lets you control the liquid flow and isolate a section of the pipe when needed. The gate valve, fitted in-line on a pipe, operates through a handwheel actuator that opens and shuts the valve.
Let's look at the main characteristics of gate valves:
Now, let's see where gate valves are typically used. They find application in various industrial environments, including oil and gas extraction sites, processing plants, and water treatment facilities. A fully open gate valve does not obstruct the flow path, resulting in a very low-pressure loss. This feature facilitates the use of a pipe-cleaning pig. Gate valves accommodate all types of fluids, including water and gas, and manage gases from -20 to 60 degrees Celsius at a maximum speed of 20 m/s. Depending on size, the valve operates within a torque range of 5 Nm and 30 Nm. Be wary of valves that operate with less than 5 Nm of torque as you might shut the valve too quickly, leading to water hammer and pressure surges in the pipeline.
When choosing the right gate valve, consider the fluid type, the required operating torque, and the temperature and flow velocity ranges. The diverse applications of gate valves and the industries that utilise them might affect your choice of gate valve. Now that we understand the technical aspects and applications of gate valves let's discuss an important factor – their cost-effectiveness.
Understanding the choice of materials for gate valves holds the key to their cost-effectiveness. For example, gate valves made from GJS400-15 ductile iron offer enhanced durability. This increased durability reduces the chance of cracking and extends their lifespan. Although these valves carry a bit more weight due to a thicker wall, the extra weight balances out a slightly lower tensile strength.
Stainless steel proves to be the most resilient material for bolts, ensuring your gate valve endures longer. Knowing how to choose the right gate valve becomes critical, and material selection significantly influences this decision. Choosing an unsuitable valve type can result in high replacement costs and significant loss of time.
The cost consideration is not just about the initial price but also potential savings in replacement costs and time. Therefore, choosing materials carefully can greatly improve gate valves' cost-effectiveness. Now that we understand the cost-effectiveness of gate valves let's look at the importance of the gate valve wedge design.
Choosing the right gate valve involves understanding the importance of wedge design. It's not just about identifying the range of designs available but also determining the one that fits your specific needs. Let's examine these aspects in more detail.
The gate valve wedge design directly impacts the efficiency of the valve and determines its suitability for specific applications. Here are the main types:
The wedge guiding system should incorporate low-friction, plastic-covered nose pieces with a groove in the body. This design ensures the valve is not difficult to operate or leak when the rubber gets damaged. For a more in-depth exploration of gate valve types, we encourage you to explore our comprehensive article titled "Types of Gate Valve."
We will discuss choosing the most suitable design for your needs.
When choosing the right gate valve for your system, consider several factors. These include pressure drop, shutoff requirements, and operating temperature/pressure. The wedge design is also essential, directly influencing the valve's performance.
Gate valves come in four main wedge designs:
Another critical aspect of wedge design is how the wedge nut attaches to the wedge. Is it a form-fit or a press-fit? Most people prefer form-fit wedges as they offer better flexibility and can usually absorb water hammers due to their freedom of play. However, this movement can irritate the rubber where the nut rests. A press-fit wedge nut can pass the force of water hammers to the spindle and the bearing, potentially bending the spindle.
The wedge nut connects the wedge to the stem. There are two basic designs: a loose design where the brass nut slides in a slot in the wedge core and a fixed design where the nut expands in the wedge core. These are suitable for moderate pressure-temperature applications to prevent the wedges from getting stuck due to metal expansion. A fixed wedge nut design is recommended as it reduces the number of movable parts, thus eliminating the risk of corrosion.
Now that you understand the importance of selecting the right wedge design let's consider another crucial aspect - the quality of rubber used in gate valves.
Also read: Exploring the Diverse Applications of Gate Valves
This section highlights the different types of rubber used and how they affect the valve's performance. Even more critical, you'll understand how to assess the quality of rubber in gate valves, a key factor in making a knowledgeable decision. Let's delve deeper into this topic.
The choice of material, especially the type of rubber, directly affects the efficiency and functionality of gate valves. These valves, widely used in various industrial applications, often have seats made from resilient materials like rubber, brass, or stainless steel. The compatibility of these materials with the regulated fluid determines their selection.
Here are some important points about rubber-seated gate valves:
When you are deciding on the right gate valve, it's important to keep in mind the specific requirements of your application. For example, if your application involves drinking water, you must ensure that the rubber parts that come into contact with the water have approval for drinking water use. The rubber components should have major approvals like DVGW/KTW, KIWA, or NF if local approvals are unavailable.
Knowing about the type of rubber used in gate valves and its effect on their performance can guide you in making a wise decision when choosing the right gate valve.
After discussing the types of rubber used in gate valves, it becomes crucial to understand how to assess their quality.
The rubber quality in gate valves significantly affects their performance and lifespan. Confirm the type of rubber used in the gate valve first. It must meet the specific application requirements, such as the fluid type, operating temperature, and pressure conditions.
To evaluate the rubber quality further, you can:
Then, check the wedge's sealing behaviour. Apply chalk over the entire sealing area and operate the valve. If the chalk shows narrow lines, the valve might not reliably stop water flow long-term or might need high actuation torques, which could stress the surrounding components.
Another vital factor is the rubber’s compression set, or its ability to return to its original shape after compression. The EN 681-1 standard specifies the minimum requirements for the compression set value. However, the better the compression set, the more effectively the rubber returns to its shape. This ensures a tight closure year after year. The rubber should also withstand continuous impact from impurities and chemicals and absorb small impurities in the seat for a tight closure.
Now that we understand the importance of rubber quality in gate valves, we can compare gate valves with other valve types in terms of functionality, efficiency, and cost.
Gate valves are renowned for their design, which involves linear motion. They employ a flat closure element that slides into the flow stream to provide shut-off. These valves successfully manage slurries and viscous liquids such as heavy oils, light grease, varnish, molasses, honey, and cream. However, they may not be optimal for low-pressure applications or scenarios that demand cleanliness or sanitary conditions.
In contrast, butterfly valves are quarter-turn valves. They utilise a metal disc mounted on a rotated rod to regulate fluid flow. These valves are versatile and can be employed in various applications, from general services to extreme conditions.
Gate valves are highly compatible with a variety of fluid types. They effectively work with water, steam, gases, and corrosive chemicals. This feature, along with their capacity to manage thick or viscous liquids, makes them a preferred choice in industries such as power plants, chemical processing, and wastewater treatment.
Before the resilient seated gate valve existed, gate valves with a metal seated wedge were preferred. These older designs needed a depression in the valve bottom to secure a tight closure.
Whether you require an electric or pneumatic actuator gate valve, a range of gate valve suppliers can cater to your needs. For larger gate valves, it's crucial to ensure that the valve can be actuated easily by the handwheel without a bypass, even at a pressure of 16 bar.
Throughout this exploration, you've understood the essential role technical specifications play in guiding you to the perfect gate valve. You've learned how the functionality, efficiency, and cost-effectiveness of gate valves are highlighted, focusing on the crucial role of wedge design and the quality of natural rubber. Remember, making an informed choice can lead to significant cost savings and improve efficiency. ‘
If you need more insights, experts from AlterValve are ready to help. We are one of India’s leading valve suppliers. Connect with our team for technical advice.
As the old saying goes, "The devil is in the details". Therefore, careful attention to detail is crucial when making wise choices.
Contact us to discuss your requirements of what is flow control valve. Our experienced sales team can help you identify the options that best suit your needs.
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