How does a sluice valve work?

Valves are necessary in any utility systems for controlling, regulating, and directing the flow of fluids. One important type of valve is the gate valve, also known as the sluice valve.

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A sluice valve uses a gate or a wedge-shaped disc to control and regulate the flow. This gate runs perpendicular to the flow of fluids into or out of the pipeline. The valve opens by lifting the gate out of the path of the fluids and enabling it to flow.

How does a sluice valve work?

Lifting the gate or the wedge is controlled by a threaded stem (a connecting rod or a shaft). The top end of the stem has a hand-operated wheel or a motor that raises or lowers the gate, while the lower end has a circular or wedge gate to obstruct the flow. The threaded stem prevents water hammering effects, as it needs to be turned several times to go from open position to closed position.

There are two types of spindles (wheels at the top of the stem used to turn the valve on and off) used for raising the gate in a sluice valve.

• A raising spindle: The spindle is attached to the gate, but the gate does not rotate with the handwheel.
• A non-raising spindle: The spindle is threaded, and the gate is also threaded where it is attached to the spindle. During operation, the valve stem does not raise but rotates in place while raising the gate.

The valve is contained within a valve chamber and has caps or handwheels to operate it and can be opened clockwise or anticlockwise.

The size of the sluice valve is usually the same size as the main valve&#;up to 300-mm diameter. There are available in bigger diameters where the size of the sluice is two-third the size of the main, but subject to a minimum of 300 mm.

When should sluice valves be used?

The simple mechanics of the sluice valve make it one of the most used valves across many industries. It is mainly used for industrial applications. You will commonly find them on process plants where they are used to manage slurries.

When in operation, these valves are either fully opened or fully closed. They are commonly used to cut off the flow of liquids and cannot be used for throttling as accuracy cannot be achieved through these valves. Besides, the high flow velocity in a partially opened valve can damage the gate, cause disk and seat surface erosion, and result in vibration and noise.

Sluice valves are often used for large pipe diameters because they are easy to use and have a simple construction than other larger valves.

What sluice valve products does Hynds have?

We stock several sluice valve products for various applications, such as potable networks, water storage, pump stations and process water systems.

Hawle E2 Gate Valves with EN or Table E Flanges

The E2 resilient seated double flanged gate valve is drilled to EN PN16 or AS Table E.

Hawle E2 Flanged Sluice Valve

The Hawle E2 Flanged Sluice Valves have flanges available in Table D, Table E, and PN16 from DN50&#;600

Hawle E3 Resilient Seated Gate Valve

The Hawle E3 resilient seated gate valve has been developed from the successful E2 gate valve with a few refinements to enhance performance.

Hawle E2 Flanged System Sluice Valve

The Hawle E2 Flanged System is a resilient seated valve with flange and socket for PE (PE 80/100) total restraint.

Hawle Service Valves

These service valves have multiple connection types to suit various applications.

Hawle A Valve with Flanged Ends

This is the world&#;s first mono-design resilient seated shut-off valve.

Hawle E2 Combi III

A flanged tee piece comprising three flanged outlets and two or three integral E2 Elypso valves.

If you need any sluice valve products or have any questions, please contact us.

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.

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How Gate Valves Work 

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

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