Sluice Valve Vs Gate Valve : What are Key Differences

Valves are very important components in utility systems. A gate valve, as the name suggests, is a type of valve that is used to control the flow of a liquid using a gate or plate. This type of valve is mainly used to completely stop or start the flow and is not used to regulate the amount of flow unless specifically designed to do so.

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The best industrial valve manufacturers follow stringent standards while manufacturing these valves to ensure quality, durability, and performance. Any kind of sub-standard quality may lead to unwanted damage and economic losses. Efficiency and ease of operation are two very important factors when choosing a valve from the plethora of vales available in the market.

 Sluice valve is called by gate valve, look through to know more info about them.

What Is A Gate Valve?

A gate valve is a type of isolation valve used to control the flow of fluids in an industrial system. A sluice refers to an artificial channel aided by a gate to control the flow of water. Sluice valves or industrial gate valves are mainly used for industrial purposes. Its easy and simple mechanics make it one of the most-used valves across various industries. The valve operates by simply moving or lifting up the barrier in the path of flowing liquids. 

It is used along the pipe in a one-directional or bi-directional flow. When fully open, it hardly provides resistance to the flowing liquid, which is one of the major reasons why it is considered very efficient. The shape of the gate maybe be parallel, but in many cases, it is kept in a shape of a wedge. Wedge gate valves help create a better sealant when closed as it applies pressure to the sealing surface and offers better sealing performance.

A gate valve works by manual rotation of a handheld wheel, or it uses an electric or pneumatic actuator. Rotation of the wheel a number of times moves the gate up and down, which controls the flow of liquid or gas inside the valve. Opening the gate provides minimal obstruction to the flow but keeping the gate half open may cause damage as the flowing liquid or gas will exert a large amount of pressure on the plate. Instead of gate valves, globe valves can be used to regulate flow. 

Operation

Although a gate valve or sluice valve is easy to operate, it consists of numerous components fixed together for it to function efficiently. This type of valve consists of the body, a gate, a seat, a bonnet, and in some cases, an actuator which automates the flow. Gate valves can be manufactured using various materials; however, stainless steel is the most preferred since the material is more resistant to changes in temperature or pressure. The various parts of a gate valve are detailed out below.

The Gate

Available in a variety of designs, the gate is the main part of a gate valve. The main design aspect of it is its sealing capacity for specific applications. A gate valve can be classified as a parallel or wedge-shaped valve based on the gate type. The former can further be divided into slab gates, parallel slide gates, and parallel expanding gates. 

Seats

A gate valve has two seats that ensure sealing along with the gate. These seats can be integrated within the valve body, or they can be present in the form of a seat ring. The latter is threaded or pressed into its position and then sealed and welded to the valve body. In situations where the valve is subject to higher temperatures, seat rings are preferred, as they allow for more variation in design.  

The Stem

The gate in a gate valve is lowered or raised when it spins on a threaded system. This can take place via a manual wheel or an actuator. An actuated gate valve can be controlled remotely. Depending on the type of step, the gate valve can be categorized into rising stem and non-rising stem valves. The former is fixed to the gate, whereas the latter is fixed to the actuator and threaded into the gate. 

Bonnets

Bonnets are valve components that ensure the safe sealing of the passage. It is either bolted or screwed to the valve body so that it can be removed for replacement or maintenance. Based on application, various types of valve bonnets include bolt bonnets, screw-in bonnets, union bonnets, and pressure seal bonnets.

Applications 

Gate valves or sluice valves have numerous applications in various industries and have diverse uses in controlling liquid, gas, and even airflow. In environmentally harsh conditions such as high-temperature or high-pressure areas in petrochemical industries, gate valves are the go-to instrument. In such conditions, the material and type of valve play an important role in the performance and efficiency of the valve.

Gate valves also find their use in fire safety systems, where a flanged gate valve is commonly used. Non-rising stem gate valves are used in ships or underground at places where vertical space is limited.  

Types Of Gate Valves

Parallel And Wedge-Shaped Gate Valves

As the name suggests, parallel slide gate valves have a flat, parallel-faced gate that is fitted between two parallel seats. On the other hand, wedge gate valves have a wedge-like gate element. This has ribs on both sides and is guided into position by the slots in the gate body. These wedge guides help transfer axial loads imposed by the medium to the valve body, enable low-friction movement, and prevent the rotation of the wedge whilst moving between open-closed positions. 

Rising Stem And Non-Rising Stem Gate Valves

The primary difference between these two types of gate valves is that they are either fixed (rising) or threaded (non-rising). In rising stem gate valves, the rotating stem rises while the valve opens. However, this valve type is not preferred where the space is limited or the installation is underground. 

Metal Seated And Resilient Seated Gate Valves

Both of these are wedge gate valves. In metal seated valves, the wedge slides toward a groove in the gate valve body and could trap solids that the fluid may contain. Hence, resilient seated valves are preferred where tighter-shut off is required, like in water distribution systems.

In resilient seated valves, a wedge is enclosed within an elastomer which ensures a tight seal. The seating takes place between the valve body and the wedge and hence does not necessitate a groove as in the case of a metal seated gate valve. Since these valves are coated with an elastomer or a resilient material, they offer a higher degree of corrosion protection.

Final Words

Sluice valves and gate valves are different names for the same type of valve. These are the most common type of industrial valves in use. As gate valves are manufactured using various materials and have numerous types, the type of valve must be selected carefully for specific applications. 

Good quality and efficient valves like the ones by Dombor are a great investment as it requires minimal maintenance in the long run, which can save a lot of money. Contact Dombor Valve today for best-in-class valves.

Introduction

Gate valves are some of the most common valves currently employed. Other common types include the plug, butterfly, ball and globe type valves.

Gate Valve Cross-Section

Gate valves are used to start and stop flow, but are poorly suited for regulating (throttling) flow. Flow through a gate valve is not proportional to the amount the gate valve is opened, that is the main reason gate valves are poorly suited to throttling. If the valve is throttled, flow through the valve has a very turbulent and high velocity, this leads to seat and disc wear.

Gate valves offer almost no resistance to flow when they are in the open position; consequently, the pressure differential across the valve is very low when the valve is open.

Like most valves, the gate valve is named after the disc it employs.

Gate valves are always linear motion valves and not rotary motion i.e. they require more than a ¼ turn in order to move from the open to closed position.

As with other valve designs, the gate valve design can be split into several sub-categories. The first category is based upon the disc shape, which is either wedge or parallel shaped. The second category is for either rising, or non-rising stem designs. Other categorisations are based upon the type of disc used:

• Solid (wedge)
• Flexible (wedge)
• Split (wedge)
• Parallel (parallel)

 

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Construction

A gate valve&#;s main components are the bonnet, disc, seat, sealing arrangement (gland seal, stuffing box etc.), stem, body and actuator.

Gate Valve Components

Gate valves can be actuated manually (handwheel) or electrically using a high torque motor.

The sliding gate (disc) can be wedge shaped (tapered) or parallel shaped. Wedge shape designs include the solid, flexible and split wedge designs.

Seat rings are used to make replacement of a worn/leaking seat easier. Seat rings have a screw thread on the reverse side which can be screwed into the main valve body, the flat surface on the opposite side is the seating surface area that presses against the disc. If seat rings are not used, it is possible to machine a flat seat on the main valve body itself, unfortunately this makes replacing the seat impossible and the seat can only be machined a few times before the entire valve must be replaced.

Gate valve bonnets are often constructed of cast iron. Cast iron is brittle and this makes the bonnet prone to cracking.  Special care should be taken when handling and maintaining valves with cast iron bonnets.

 

As the stem penetrates through the valve bonnet, it is necessary to install a sealing gland to prevent leakage occurring through the gap between the stem and bonnet; sealing is usually achieved using a fibrous packing material.

Flanges are installed on the suction and discharge side of the valve so that piping can be easily connected.

 

How Gate Valves Work 

The below video is an extract from our Introduction to Valves Online Video Course.

 

Yaxing Valve Product Page

The sliding gate (disc) is lowered at a right angle into the flow path until it reaches the valve seat where it seals and stops the flow completely. To open the valve, the sliding gate is retracted into the bonnet.

 

Service Conditions

Gate valves are typically employed for temperatures between -20 to 60 °C, pressures up to 16 bar(g) and flow rates of between 5 (liquids) to 20 (gasses) metres per second. Higher pressures cannot be achieved as damage to the packing would occur.

 

Rising and Non-Rising Stem Designs

Gate valves are classified as rising, or, non-rising stem. `Rising` refers to the stem and if it rises out of the valve bonnet as the valve is opened.

Rising Gate Valve

&#;Non-rising&#; refers to the stem not rising from the valve bonnet irrespective of the valve position.

Non-Rising Gate Valve

Rising stem designs remove both the disc and the stem from the flow path when the valve is open. Non-rising stem designs usually leave the stem within the flow path when the valve is open, although it is also possible to house the stem completely within the disc.

The non-rising stem gate valve is preferred if the ambient environment is corrosive e.g. sea spray etc. and it is not desirable to leave the stem permanently exposed when the valve is open. Conversely, if the flowing medium is corrosive, the non-rising valve may not be a good choice because the stem remains within the flow path when the valve is open.

For non-rising stems, the stem rotates within the packing but does not move vertically, thus there is little risk of dirt or foreign particles damaging the packaging or entering the system.

Non-rising valves are almost always fitted with a local visual pointer which indicates the position of the valve.  The rising stem design is preferred if quick local visual indication is desired (it is easy to identify if the valve is open or closed with the rising stem design).

 

Inclined Disc Designs

Solid Wedges

Solid wedges are the simplest, strongest and most suitable for many flowing mediums. Solid wedges are often manufactured from a single metal piece and the disc seat area size matches the valve seat area size.

Flexible Wedges

Flexible wedges are machined around the wedge perimeter in order to help the disc locate the seating surface more easily. The size of the machined area should not be too large as this reduces the strength of the disc (a thinner disc is a weaker disc).

Flexible wedges are employed for systems operating with large temperature fluctuations. As the system temperature changes, the piping and valve dimensions also change due to the coefficient of thermal expansion. Having a flexible/variable seating area allows the valve to seat correctly even with some expansion and contraction of parts.

Flexible Wedge Example

A solid wedge valve is installed within a steam system. If the valve is in the closed position when the system is hot, the wedge may become locked/jammed against the valve seat once the valve components temperature decreases. This renders the valve totally inoperable and it will remain in the closed position until the system temperature again reduces, or, until all valve parts reach the same temperature. This type of problem is referred to as &#;valve binding&#;.

Split Wedge

Split wedges offer flexible seating on both the suction and discharge side of the wedge. The wedge consists of two separate halves with each one being able to self-align in order to seat correctly; this self-aligning feature is made possible due to the flexibility obtained when using two separate halves for one wedge.

Parallel Disc Design

Parallel Disc

Parallel sliding discs utilise a spring placed between the two parallel discs. The spring is held under compression between the parallel discs and thus exerts constant force outwards onto the internal surfaces of the discs. As the valve is lowered into the valve seat, the spring is further compressed and the resultant force exerted by the spring ensures each disc is pressed firmly against the seat.

Parallel disc type valves can be used for both high and low pressure applications. The valve is well suited for any system where there are large temperature fluctuations.

 

Advantages

The gate valve is very simple in design, relatively cheap and easy to maintain.

There is almost no pressure drop across the valve when the valve is in the fully open position.

Replacement of the gate valve disc is usually not a difficult task.

Replacement of the seat rings is usually not a difficult task.

 

Disadvantages

Gate valves are not well suited to throttling (any valve position between fully open and fully closed) as this creates turbulent flow and frictional losses. A valve left in the almost closed position will cause the flowing medium to flow at very high velocity across the valve&#;s seating surfaces, this can lead to damage of the surfaces (&#;wire-drawing&#;) and passing/leaking of the valve.

Gate valves create turbulent flow when throttled and experience excessive vibration as a result. This situation should be avoided to prevent damage occurring to the valve packing and other internal parts.

Compared to a globe valve, a gate valve&#;s seating surfaces are more difficult to refurbish (if seat rings are not used).

 

 3D Model Details

This 3D model shows all major components associated with a typical gate valve, these include:

• Handle/Actuator
• Stem
• Bonnet
• Body
• Gate/Disc
• Seat

 

Additional Resources

https://en.wikipedia.org/wiki/Gate_valve

https://www.avkvalves.eu/en/insights/product-insights/gate-valves/what-is-a-gate-valve

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