Flow Patterns Drum Screen

Hubert drum screen animation

Dual Flow vs Centre Flow

Hubert designs screens based on dual flow or centre flow

Hubert supplies  both ‘Dual Flow’ and ‘Center Flow’ pattern.  Dual flow is often chosen for new plants. Center flow is of course also used, regularly in renovation projects. Hubert has extensive experience with both configurations.

A ‘Dual Flow’ configuration has some advantages against ‘Center Flow’. In case of a newly built plant, Hubert advises the ‘Dual Flow’ pattern.

 

Below you can find a comparison in drum screen flow patterns. Please contact us in case of questions.

 

Vertical Drumscreen – Flow Patterns

The diagram below shows the difference between dual flow (inside to outside) and center flow (outside to inside).

Hubert drum screen flow directions
Hubert flow patterns drum screen

Comparison in drum screen flow paterns

Flow configuration

Dual Flow in-out

Universal, flow to the pump is laminar and not turbulent.

Centre Flow out-in

At low tade the drum screen has to be submerged for at least 1/3 diameter, otherwise debris which sticks to the mesh in the lowest part can fall back or flushed away by high speed rotation before the retaining lips.

Debris & Wash water collecting throughs (maintenance)

Dual Flow in-out

Can be inspected & cleaned easily from operation floor on both sides.

Centre Flow out-in

Can be inspected & cleaned easily from operation floor.

Cleaning & adjustment nozzles & spraypipe (maintenance)

Dual Flow in-out

Washwater jets clean the mesh by sending a fan of pressurised water to remove debris from the screen. Jets do unfortunately block. With this flow type the jets are easily accessible by the operator for inspection, adjustment or cleaning, without stopping the screen.

Centre Flow out-in

The drum screen has to be stopped in order to reach the spray pipe & nozzles. So mechanics have to climb into the pit / drum screen to reach the nozzles, whcih can be very complicated if you don’t have the right facilities available.

Check & replacement of main bearings (maintenance)

Dual Flow in-out

This is quite easy. the drum screen can be supported on the concrete foundation.

Centre Flow out-in

This is very complicated, because the bearings (having a large diameter) are located in the pit on the fixed hollow shaft and therefore are charged with the full load. For this reason it is difficult and consequently time-consuming to replace these bearings.

Spray pipe efficiency 

Dual Flow in-out

The spray pipe efficiency is very high. All energy can be used for cleaning, debris falls down in the throughs because the force of gravity is also very effective.

Centre Flow out-in

The spray stream has to blow the debris into the through, but is not cooperated in this but is counteracted by the gravitational force. This results in debris always falling back between drum screen and through. As a result, the water pressure and required capacity is normally 30% higher.

Operation floor / bottom level

Dual Flow in-out

No difference.

Centre Flow out-in

No difference.

Drum screen width

Dual Flow in-out

Limited to approx 7 m, caused by the Hubert A-spoke construction).

Centre Flow out-in

Limited to approx 10 m.

Power consumption

Dual Flow in-out

Very low, rotates along flow direction.

Centre Flow out-in

Very high, caused by the friction in the bearings (> diameter), because piping of the spraypipe passes through the bearing. So the hollow shaft does not rotate and consequently, the drum screen rotates around the shaft. The drum rotates against the flow direction, which not only causes a higher power consumption, but also a disturbance of the collection of dirt (especially at higher speeds). This can potentially lead to 2-3 times higher power consumption.

Civil construction and clogging

Dual Flow in-out

Here is an additional load on the concrete construction. Headloss results in compressive forces on the civil works which supporting the main bearings (concrete is at its strongest in compression).

Centre Flow out-in

There is a pulling force on the anchors of the bearing. For example, a drumscreen: dia 16m; width 4.4 m; 1,5 mwc can give a pulling force of 1.050 kN. This force is only partially compensated by the weight of drum screen. When the anchors or cailipered bolts break out, the drum screen will rise and fall back into the pit.

Debris collection efficiency

Dual Flow in-out

The reaining lips will minimize the possibility of falling back during the upwards rotation. Trash moves naturally to the elevating faces which is very important with dense trash, jelly fish and fish recovery. The debrisis is easily collected in the complete range of all possible water levels.

Centre Flow out-in

When only the lowest part of the drum screen is submerged, the debris on the drum surface will fall back into the water during the upwards rotation, before it reaches the upper half of the drum screen (because then it will be taken by the retaining lips). Depending on the debris type, up to 25% s not included!  Therefore this type of flow pattern is not very effective whren it is not submerged for at least 1/3 of the diameter.

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