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DAGYEE External Drum Screen Systems: The Complete Technical FAQ

Introduction to DAGYEE Filtration Solutions

About This Guide:

This technical guide is intended for environmental engineers, plant managers, and procurement specialists who are designing Wastewater Treatment Plants (WWTP) or managing industrial effluent. As a specialized manufacturer, DAGYEE focuses on engineering high-performance External Drum Screens (also known as Rotary Drum Screens). Unlike standard off-the-shelf units, DAGYEE specializes in customizing the drum dimensions, slot gaps, and material specifications to meet your specific hydraulic and solids loading requirements.

Section 1: Fundamentals & Working Principles

Q1: What exactly is an External Drum Screen, and how does it differ from other screens?

An External Drum Screen is a mechanical, self-cleaning filtration device used for Solid-Liquid Separation in the primary stages of wastewater treatment.

The "External" Concept: Unlike internal feed screens where water enters the center of the drum, in a DAGYEE External Drum Screen, the raw wastewater is fed onto the outside surface of the rotating drum.
The Mechanism: The drum rotates continuously. The liquid passes through the screen openings (slots) and enters the inside of the drum, flowing out completely clarified. The suspended solids are retained on the outer surface of the cylinder.
Separation: As the drum rotates, the trapped solids are transported to the top of the cycle, where a Scraper Blade (doctor blade) peels them off for discharge.

This design is generally superior to static screens because the rotation actively removes solids, preventing the "blinding" (clogging) that plagues stationary filters.

Q2: How does the "Wedge Wire" profile enhance performance?

The heart of the DAGYEE External Drum Screen is the Wedge Wire Screen drum. We do not use perforated plates or simple wire mesh.

V-Shaped Profile: The wires are triangular (V-shaped). The flat side faces the incoming flow (outside), and the pointed side faces inward.
Non-Clogging Design: This geometry ensures that there are only two contact points for any particle. If a particle is small enough to pass the surface gap, it immediately falls through the widening gap behind it. This virtually eliminates clogging or "pegging" of solids within the slots.
Hydraulic Efficiency: The smooth surface of the Wedge Wire utilizes the Coanda effect (surface tension), helping to shear water away from the solids, resulting in drier discharged screenings compared to mesh screens.

Q3: Why is this considered a "Primary Screening" device?

Primary Screening is the first line of defense in a treatment plant. Its goal is to remove gross solids, trash, and heavy organic load before the water reaches sensitive downstream equipment (like pumps, aeration tanks, or membranes).

Using a DAGYEE External Drum Screen at the headworks significantly reduces:

TSS (Total Suspended Solids): Typically reduces TSS by 30%–60%.
BOD/COD: By removing the organic solids before they dissolve, you reduce the biological load on your secondary treatment, saving energy and chemicals.

Q4: What is the function of the Overflow Weir?

The Overflow Weir is a critical component located in the headbox (distribution tank) of the machine.

Flow Distribution: It ensures that the wastewater is spread evenly across the entire width of the rotating drum. Without an even distribution, you would only use a fraction of the screen's surface area.
Velocity Control: It regulates the speed at which the water hits the screen. If the velocity is too high, it might force soft solids through the slots. The weir ensures a gentle, laminar flow onto the screen surface.

Section 2: Technical Specifications & Design

Q5: What "Slot Size" should I choose for my application?

The Slot Size (the gap between wires) determines the filtration precision. DAGYEE customizes this ranging typically from 0.15mm to 3.0mm.

0.15mm – 0.25mm: Ultra-fine screening. Used for recovery of valuable fibers (pulp & paper) or removing fine hairs/grit.
0.50mm – 1.0mm: Standard for Food Processing Wastewater and slaughterhouses. Removes skins, seeds, vegetable scraps, and meat trimmings.
1.0mm – 2.0mm: Typical for municipal sewage to protect downstream pumps.
Trade-off: Smaller slots capture more solids but reduce the Flow Rate (throughput). DAGYEE engineers will calculate the optimal balance for your facility.

Q6: What materials are used in construction?

Corrosion resistance is non-negotiable in wastewater.

SS304 Stainless Steel: The industry standard for municipal sewage and general non-corrosive industrial water.
SS316/316L Stainless Steel: Mandatory for high-chloride environments (seafood processing, tanning), acidic wastewater, or high-temperature applications.
Scraper Material: The Scraper Blade is typically made of wear-resistant Brass, Nylon, or hardened Polyurethane, designed to scrape the drum cleanly without damaging the stainless steel wires.

Q7: Is the system designed for Continuous Operation?

Yes. The DAGYEE External Drum Screen is a Continuous Operation device.

It is driven by a high-efficiency gear motor.
It is designed to run 24/7 without manual intervention.
Unlike a filter press that runs in batches, the drum screen constantly accepts feed and discharges solids, making it perfect for continuous industrial production lines.

Q8: Can DAGYEE customize the dimensions?

Absolutely. This is our core strength. We do not force you into a standard catalog size.

Drum Diameter: Determines the hydraulic capacity and peripheral speed.
Drum Length: Determines the filtration surface area.
Headbox Height: Modified to fit your existing pipework or channel height.

We can engineer the machine to fit into tight spaces or replace existing, obsolete screens without requiring major civil engineering work at your site.

Section 3: Operational Performance & Maintenance

Q9: How does the Self-Cleaning mechanism work?

The term Self-Cleaning refers to the combined action of rotation and scraping.

Rotation: As the drum turns, it constantly presents a clean surface to the incoming water.
Scraping: The solids that stick to the drum are carried over the top. The Doctor Blade (scraper) mechanically shears these solids off.
Backwashing (Optional but Recommended): For sticky wastes (like grease or starch), we install an internal Spray Nozzle system. This sprays water from the inside out to dislodge any particles that might be wedged in the slots, ensuring the screen remains open.

Q10: What happens if the screen clogs (blinding)?

While Wedge Wire is Clog-Resistant, severe blinding can occur if sticky grease (FOG) is present without proper cleaning.

Solution: Activate the internal spray bar.
Solution: Check the tension of the scraper blade. If the blade is worn or loose, it won't peel the solids off effectively, leading to buildup.
Design: DAGYEE designs the scraper assembly with adjustable tension springs to maintain perfect contact pressure as the blade wears over time.

Q11: What is the moisture content of the discharged solids?

While the primary goal is separation, the External Drum Screen provides a basic level of dewatering.

The solids spend time on the top arc of the drum, allowing free water to drain back through the screen.
The result is "drip-free" screenings, typically having a moisture content of 80-90%.
If you need drier solids (e.g., for incineration or composting), we recommend feeding the output of the drum screen into a Screw Press Dewatering machine (which DAGYEE also manufactures).

Q12: How much energy does the system consume?

External Drum Screens are incredibly energy-efficient.

The rotation is slow (typically 5–10 RPM).
There is no high-pressure pumping required (gravity flow).
A large unit treating 500 m³/hr might only use a 1.5 kW or 2.2 kW motor.

This Low Energy Consumption makes it one of the most cost-effective treatment methods available (OPEX).

Section 4: Applications & Industries

Q13: Why is this popular in the Food Processing industry?

Food Processing Wastewater is high in organic suspended solids (vegetable peels, potato starch, fruit pulp).

These solids are often valuable. A DAGYEE screen allows for the recovery of these by-products for use in animal feed.
Food waste rots quickly. The rapid, continuous removal prevents the solids from fermenting in the water, reducing odors and BOD load.
The Sanitary Design (Stainless Steel) allows for easy washdown and hygiene compliance.

Q14: Can it handle Slaughterhouse (Abattoir) waste?

Yes, this is a key application.

Materials: Feathers, paunch manure, hair, and fat trimmings.
Challenge: Feathers and hair are notorious for blinding mesh screens.
DAGYEE Solution: The continuous scraping action combined with a 0.50mm to 0.75mm slot size is extremely effective at rolling feathers off the drum surface without them getting "stapled" into the holes.

Q15: Is it suitable for Textile and Paper industries?

Textile: Used for removing fibers, lint, and wool from dyeing and washing water.
Pulp & Paper: Used for Fiber Recovery. The screen captures usable pulp fibers that would otherwise be lost to the sewer, returning them to the process and saving money.
Plastic Recycling: Used to remove paper labels and dirt from the wash water in PET bottle recycling lines.

Q16: How does it handle oil and grease?

If the water has free-floating oil, the External Drum Screen is not an oil separator. However, it can handle greasy solids.

For high grease applications, we recommend a Hot Water Spray System on the internal nozzles to melt grease build-up on the wires.
Typically, the drum screen is placed before a DAF (Dissolved air flotation) unit to remove the solids so the DAF can focus on the oil.

Section 5: Troubleshooting & Safety

Q17: What flow rate can DAGYEE screens handle?

We scale the machine to the flow.

Small Units: 10 – 30 m³/hr.
Medium Units: 50 – 200 m³/hr.
Large Custom Units: Up to 1000+ m³/hr (often achieved by running units in parallel).
Note: Flow rate depends heavily on the slot size. A 0.25mm screen handles much less flow than a 1.0mm screen of the same physical size.

Q18: Is the system enclosed for odor control?

Yes.

Standard units can be open, but for municipal or odor-sensitive food plants, DAGYEE provides a Fully Enclosed Cover (Stainless Steel hood).
This contains odors and spray mist.
We can also provide a flange connection on the cover to connect to your facility's odor extraction/ventilation system.

Q19: What are the consumable spare parts?

The External Drum Screen is a low-maintenance machine. Spares are minimal:

Scraper Blade: This sacrifices itself to save the drum. Needs replacement every 6–12 months depending on usage.
Seals: Rubber seals around the drum edges.
Bearings: Standard greasing required.

DAGYEE keeps these parts in stock for quick global shipment.

Section 6: Commercial & Purchasing

Q20: What information does DAGYEE need to provide a quote?

To engineer the correct solution, we need:

Water Source: (e.g., Sewage, Tomato Wash Water, Pig Manure).
Flow Rate: Peak and Average (m³/hr).
Solid Content: TSS (mg/L or %).
Particle Size: What is the target size to remove?
Slot Size Preference: (If known).
Material: (SS304 or SS316).
Discharge Height: Do you need the machine on high legs to dump into a hopper?

Q21: Can DAGYEE integrate this into a skid system?

Yes. We often build integrated skids that include:

The External Drum Screen.
A feed pump.
A collection tank.
A control panel (PLC).
A sludge screw conveyor.

This "Plug and Play" approach saves you installation time and ensures all components are hydraulically matched.

Q22: What is the typical lead time?

Standard Models: 3 – 4 weeks.
Custom Dimensions: 5 – 6 weeks.

All units are fully tested (dry run and motor checks) in our factory before crating.

Q23: Why choose DAGYEE over other suppliers?

Factory Direct: You are dealing with the manufacturer, not a trading company. This ensures better prices and direct technical support.
Customization: We don't say "no" to unique size constraints.
Quality: We use precision welding for our Wedge Wire drums to ensure uniform slot gaps across the entire cylinder.
Experience: We have years of experience in challenging Industrial Wastewater sectors like tanning and slaughterhouses.

Summary: The DAGYEE Advantage

The External Drum Screen is the workhorse of physical separation. Whether you are protecting a membrane bioreactor, recovering pulp fiber, or simply trying to reduce your municipal surcharges for TSS, the efficiency of the screen depends on the quality of the Wedge Wire and the precision of the manufacturing.

At DAGYEE, we combine robust engineering with flexible manufacturing to deliver screens that fit your process perfectly. We ensure that your Filtration Precision is met and your maintenance costs are minimized through our superior Clog-Resistant designs.

Ready to Clean Up Your Water?

Do not settle for standard screens that blind or rust. Get a screen engineered for your specific waste stream.

Contact DAGYEE today for a technical consultation, dimension drawings, and a competitive proposal.