Filson Coanda Screen

Filson Coanda Screen

Your Trustworthy Coanda Screen Manufacturing Expert In China

Filson Coanda screen, also called Coanda effect screen, is a precision water treatment screen, combining with Coanda effect and wedge wire technology. It has been successfully used for solids and debris removal in hydropower plant intakes, water conservation schemes, and agricultural irrigation.

If you have an urgent or a large quantity order, just contact Filson! We can guarantee to satisfy your needs immediately with our plenty of Coanda screen for sale. Furthermore, OEM service is always our strength.

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Coanda Screens: The Ultimate FAQ Guide

Choosing suitable Coanda screens can be a difficult process.

A reason this guide explores everything you need to know about the Coanda screens such as design, features, material type, and applications, just to mention a few.

Keep reading to learn more.

What Is A Coanda Screen?

The Coanda screen is a form of water intake that is self-cleaning and static, requiring no electricity and little maintenance.

Also, the Coanda screen employs a wedge-wire screen constructed in the form of an Ogee-shaped slope.

Furthermore, the ogee slope above the screen is determined by a solid acceleration plate.

The slope generates the high sweeping velocities required for self-cleaning.

Flat wedge-wire is the most basic sort of Coanda screen encompassing wedge-shaped wires welded to backer rods below the screen.

The close spacing of the wires allows fluid to pass through while preventing passage of solids.

Coanda screens will reliably operate depending on the slot opening.

A Coanda Screen

What Are Some Of The Constraints Associated With Coanda Screens?

A major constraint with the Coanda screens is head loss that occurs between the weir crest and the screen foot.

While you can accommodate this constraint in some screens, it can be challenging where you have inadequate hydraulic design.

Another constraint you observe with Coanda screens is the length of weir necessary to produce certain capacity.

A flow rate of 1m³/sec would necessitate a weir over 7m long, based on typical flow rates of 140l/sec per metre.

Where you already have a weir, you can increase the height of the crest and construct a sump compartment downstream.

However, enlarging the width frequently necessitates removing wing walls and even widening the watercourse.

Where you cannot raise the crest, you may find issues with air entrainment in the pipeline depending on the hydraulic design.

You can lose up to 1.3 metres of submergence at the pipe mouth if the pipe remains at the same level.

When it comes to the environment, the biggest constraint is the work of construction.

However, Coanda screens are preferable since their one millimeter spacing prevents the tiniest fish from penetrating the pipeline.

Why Should You Employ Coanda Screens?

You find the following pros in employing Coanda screens:

• Self-cleaning features result in a mostly maintenance-free operation, reducing time and associated expenses.
• Reliable supply of screened water increases hydro plant running time, production, and efficiency.
• You can adjust slot gap sizes to screen trash with diameters ranging from 0.2mm to 2mm.
• Because there are no mechanical moving parts, there is no need for costly maintenance or a power source.
• Highly durable screen construction resists abrasive material and corrosion.
• Coanda screens have proven operational effectiveness even at low temperatures without freezing in some of the world’s harshest regions.
• In fisheries conservation areas, Coanda screens are trusted not to harm fish stocks.

Coanda Screens Are Operational In Cold Temperatures Without Freezing

How Does A Coanda Screen Work?

You typically install Coanda screens on an intake weir’s downstream face.

The flow delivery is at the defined angle and velocity required by screen’s separation area via an ogee-shaped acceleration plate.

The Coanda effect ensures constant screen surface contact.

You employ Wedge wire to screen dirt and particles away by positioning them at precise and constant slot gap tolerances screens.

The screened water that flows through the open area accumulates in a chamber underneath it before delivery to pipelines.

Also, the wedge wire’s tilt angle offers an additional shearing effect that increases throughput.

The flow is due to a combination of orifice flow via slots and flow shearing due to offsets by inclined wires.

Besides, the orifice flow component is proportional to the depth of water above the screen and the slot width.

Alternatively, the sheared flow component is proportional to the offset height and the velocity across the face of the screen face.

The sheared flow aspect is enhanced as the flow rushes down the Coanda screen face.

An Image Showing How A Coanda Screen Works

What Steel Types Can You Employ In Constructing Coanda Screens?

You find Coanda screens furnished from various variants of stainless steel such as SAE 304, SAE 304L and SAE 904L.

SAE 304 is the most common with chromium and nickel elements as the principal non-iron elements.

SAE 304L contains chromium, nickel and molybdenum alongside iron with smaller amounts of silicon, phosphorus, and sulfur.

Molybdenum enhances corrosion resistance than the SAE 304 especially from point attacks by chlorides and reducing acids.

SAE 904L also employs molybdenum and copper greatly enhancing its corrosion resistance especially by reducing acids such as sulphuric acid.

Its high alloying concentration also strengthens its resistance to cracking.

What Are The Main Features Of A Coanda Screen Assembly?

A Coanda screen assembly has the following main features:

Acceleration Plate

The acceleration plate is a compact even plate located above the screen.

Furthermore, the acceleration plate delivers water to the screen at the right pace and in the desired direction.

Also, the acceleration plate drop determines the minimal water velocity required for self-cleaning.

The acceleration plate also smooths the water before delivering it to the screen at the proper angle.

Screen

The screen panel is usually a concave arc with a radius of curvature of 10 to 12 feet.

You can however, also employ planar screen panels.

The screen employs an inclined wedge wire to slice through the bottom water layer.

You can detach the screen panel to carry out maintenance or for replacement.

You install the screen on a hollow overflow weir’s downstream face.

The wedge-wire screen’s orientation is horizontal and perpendicular to the flow direction with the flow coming from the acceleration plate.

Mounting Angle

Mounting angle fastens the system to the framework and provides leveling bolts for rapid installation adjustments.

The primary goal is to provide smooth flow acceleration as it descends over the crest.

Additionally, it serves to convey the flow tangent to the surface of the screen at its upstream rim.

The acceleration plate and weir’s crest can be as simple as a circular arc or an ogee-shaped profile.

The most common tilt angle is 5°, however you find many manufacturers providing angles ranging from 3° to 6°.

You can also modify the tilt angles during the manufacturing process.

Why Should You Install Coanda Screens On A Slope?

When you install Coanda screens in a flat design, the collected dirt will gather at the top.

The depth of debris would delay the flow of water through the screen, even if the screen apertures do not plug.

Installing the Coanda screen on a slope ensures you have no debris at the top area.

The sloping formation allows some water passage via the slot apertures, while particles brush down the screen.

For cleaning material off the screens, Coanda screens employ minimum water velocity across the screens.

Coanda Screen Should Be Installed On A Slope To Avoid Debris Collection

What Wire Types Can You Employ In A Coanda Screen?

You can employ two common wire types in a Coanda screen:

Flat Wedge-Wire

A Coanda screen employing a flat wedge wire utilizes the weight of the water to force through the slot openings. You refer to this as an orifice flow.

You can incline the flat wedge-wire Coanda screen to eliminate debris.

In this case, the flow velocity increases thereby decreasing the orifice flow.

When self-cleaning, you need an increased flow velocity at the intake.

Consequently, you observe a reduced flow through the flat wire.

Tilted Wedge Wire

You find tilted wedge wire best placed when faced with high velocities versus screen flow.

The wedge wires you employ in tilted wedge screens are similar to those of the flat screen differing in tilt.

You attach the wires to the backing rods by welding at an angle.

The prominent wedge wire edge extends to the flow slicing the water in what you refer to as shearing flow.

The shearing flow increases with increasing water speed across the screen.

Coanda Tilted Wedge Wire Screen

Why Is The Screen Approach Important In Coanda Screens?

A well-designed acceleration plate is necessary for water to smoothly interact with the screen at the exact angle.

When water arrives at the screen in a laminar flow at the desired least speed, the screen functions to full potential.

The edges of the routes onto and off the screen are razor-sharp. The water flow is turbulent and unsteady, and the water bypasses the top screen segment.

As a result of this design, screen performance will decrease. The erratic water flow from the screen will damage the streambed beneath the intake.

The acceleration plate and the weir make a smooth approach onto a rounded screen.

Besides, the water gets smooth and rapid as it rushes down the acceleration plate.

The discharge water is almost at the same level as the surrounding water.

Also, the dip and curvature of the acceleration plate are tailored to the intake site requirements.

What Are The Design Parameters Of A Coanda Screen?

You find the following design parameters influence the functionality of a Coanda screen:

• Structural design of the Coanda screen includes aspects such as the drop height. This covers the height from the upstream pool to the beginning of the screen.
• Slope, length and curvature of the screen.
• Width of the Coanda screen’s slot and wire and the wire’s angle of inclination.
• Hydraulic conditions which influence the screen flow affecting bypass flow and screen backpressure and tail water.

Design Parameters Of A Coanda Screen

What Are The Basic Concepts Of The Coanda Screen Capacity?

You express the Coanda screen capacity as a product of volume and time known as discharge.

Discharge describes the flow through the screen per unit width hence unit discharge.

You have three important unit discharges for the Coanda screen.

The input to the screen over the crest, the bypass flow over the screen and the flow through the screen.

Bypass flow is absent at reduced inflow rates, and all flow passes via the screen.

You note that a section of the screen downstream is dry.

The wetted screen length increases as intake increases, until the screen is fully drenched, when eventually bypass flow begins.

Upon increasing intake, bypass flow and screen flow also increase with increasing flow depth over the screen.

What Is The Relationship Between The Coanda Screen Incline And Drop Height?

The accelerator plate creates a smooth transition from the calm flow upstream to the rapid flow across the screen.

For best results, the flow should accelerate smoothly and delivered tangent to the screen surface.

An ogee shape provides the optimal accelerator plate profile where you have a free-falling jet under gravity’s influence over a weir.

As the flow passes over the weir, this shape fully supports it.

When you need a precise screen inclination angle, you define the slope along the ogee-shaped curve. Additionally, you have to mount the screen at that point, tangent to the ogee form.

As a result, the ogee shape determines the drop height for a particular discharge and screen angle.

Similarly, when you want a specified vertical drop height, you have to evaluate the screen slope.

What Happens When You Alter The Accelerated Drop Height Of A Coanda Screen?

Consider a screen erected at a 10° inclination, the capacity increases considerably with a decreasing drop height.

You note that this impact diminishes with steeper inclination angles.

Therefore, at a 60° incline angle, the screen capacity is lowest at a drop height of around 0.1 m.

You find that this increases marginally where you have higher drop heights.

The rationale for these discrepancies is because flatter screens have more orifice flow component and smaller shearing flow component.

When you reduce the accelerator drop height, you increase orifice flow because the flow depth above the screens is increased.

How Does The Screen Slope Affect The Performance Of A Coanda Screen?

With changing screen angle, discharge through the screen varies linearly.

Changing the wire tilt angle positively or negatively affects capacity, with greater effect at steeper slopes with pronounced shearing flow.

You can alter the screen porosity by adjusting the widths of the slot or wire.

You find these changes influence performance more at low screen angles, where orifice flow is prominent than shearing flow.

How Does The Screen Length Influence Coanda Screen Performance?

The total screening capacity of a Coanda screen is proportional to the screen length.

You find that the screen capacity increases nonlinearly when you increase the screen length.

However, when you alter the surface properties of the screen unrelated to the length, it may affect the Coanda screen capacity somehow.

Such properties include the wire tilt angle and the widths of the slot and wire.

Does The Screen Curvature Of A Coanda Screen Influence Performance?

You find more common use of concave screen panels for Coanda screens.

The shape allows a steep slope at the screen’s intake and a gentle slope at the screen end.

You can compare a planar screen construction and concave screen sharing similar total vertical drop and stream width.

In this case, you find the concave screen panel necessitates a slight gain in the length of the screen.

Where you have a concave panel, the screen face pressure increases resulting in a positive adjustment of the flow’s orifice component.

Altering the arc radius changes the discharge angle at the screen bottom as well as the head drop.

When you increase the curvature of a Coanda screen you increase its capacity.

However, this negatively affects the total head across the screen which reduces.

What Are Some Of The Important Coanda Screen Properties That Influence Performance?

You find the screen properties of wire tilt angle and width as well as slot width considerably influences the screen capacity.

Respective slot and wire width determine the screen porosity, which in turn influences the flow component on the screen.

When you reduce the screen incline angle, you find the influence of slot width on screen capacity increases.

The screen discharge decreases as you increase the width of the wire and is more pronounced at smaller screen inclines.

Where you have bypass flow, you notice width of the wire has greater influence on the screen capacity.

The tilt angle and screen discharge have a direct linear relationship whose effect is largely visible in steeper screens.

When operating flatter screens, you experience larger capacities compared to steeper screens.

You allude this development to the greater orifice flow component you have in the former.

How Can You Come Up With An Effective Coanda Screen Design?

When designing a Coanda screen, you focus on three aspects: the desired head, the total flow capacity and the screen length.

The screen slope greatly influences these aspects and you have the choice of using a concave screen or flat panel.

Where you employ a steep screen with accompanying accelerator drop, you conduct less cleaning.

A concave panel increases the screen flow while reducing the discharge angle at the base.

A flat panel allows you to extend your screen length and thus suitable where you require higher capacity.

A curved screen is undesirable as it flattens toward the base posing the problem of accumulation of dirt.

You also note the accelerator plate is important during design since it influences the flow velocity.

Sufficient flow velocity is necessary for self-cleaning and flow alignment as it enters the screen.

A common way you furnish the accelerator plate is in an ogee crest shape.

You can also present these plates with a smooth curvature with a gradual slope ensuring flow sticks to the crest.

A Smooth Curvature Slope Is Handy In Coanda Screen Design

Other Products You May Like:

• Intake Screen
• Johnson Screen
• Hydro Screen
• Well Screen
• Wedge Wire Screen

For all your Coanda screens, contact us now.