Designing and installing a new screen for Clifton Maybank water abstraction point on the River Yeo
With the successful completion of the two screens at Wessex Water’s Albert Street Pumping Station, they were keen for GoFlo to design a new screen for Clifton Maybank water abstraction point on the River Yeo.
Detail of travelling screen installation at Clifton Maybank.
The maximum abstraction flow rate at Clifton Maybank being 0.104 m3/sec. , with a required screen mesh size of 3mm, and a maximum approach velocity requirement of 0.25 m/s would normally be a relatively simple solution, but with a non-standard shape inlet structure for a mechanical screen and low water levels would prove to be more of a challenge.
Existing non-standard inlet on site.
Design of new travelling screen
The inlet chamber at Clifton Maybank did not lend itself to the fitting of a mechanical screen due to its angled walls, with internal penstock and overhead power lines, ruling out the use of a crane for installation.
The standard GoFlo screen design incorporates a pivoting guide frame to simplify installation into the channel: This could not be used at this location due to height restrictions, so a lifting frame and guide rail system was designed to facilitate the installation and removal from the channel without the need of a crane.
Section showing screen in chamber.
Section showing screen lifted out of chamber.
3D model of complete installation.
Installation
Screen guide frame in position.
Note white rollers at the top: These allow the screen to pivot smoothly from horizontal to installed position and vice versa.
GoFlo travelling screen showing white rollers.
Left side of screen: Filler plate between edge of screen guide frame and wall had to be contoured to fit.
Right side of screen: Two-part filler plates needed to follow the penstock steelwork with less than 3 mm gap (although most of the panels fitted with less than 2 mm!)
No crane required! A porta-gantry was used to raise one end of the screen off the trailer so it could be lowered onto the first set of rollers. With the screen resting on the rollers, the porta-gantry could be disconnected and relocated at the other end of the screen, lifted and moved forward until the whole screen was resting on the rollers.
Travelling screen showing crane used for installation.
With the screen resting on the rollers, a chain block and spreader beam are used to lift/pivot the screen. Pivot blocks are bolted into position on the screen chassis legs to create a pivot point. These are removed once the screen is at the correct angle, allowing the screen to be lowered into the chamber.
Pivot blocks are bolted into position.
Lifting and pivoting the screen.
The existing bar screen provides protection from large objects hitting the face of the screen. Although the 3 mm mesh screen is relatively strong, objects such tree branches could pierce the screen face if they had a large enough mass
Travelling screen in its operating position.
Travelling screen detail.
Completed screen and debris trough. The trough incorporates a removable centre section to allow the screen to be lifted out the chamber with minimum disassembly.
