Falkirk Wheel Doors and Seals
The caissons on the Falkirk Wheel don't use traditional lock technology. The unique design called for an alternative approach to sealing the caisson ends.
Because of space limitations, and the need to limit the amount of water "trapped" when the gates or doors close normal vertically hung doors were discounted.
This image 26th May 2002
The doors are raised from a recess in the base of the caisson.
This shot of the caisson before it was completed (22nd
August 2001) clearly shows the recesses in the caisson at either end where
the door lies when it is open. Although having the door located underwater when
open requires more automation and maintenance, it allows the door to take up
less space in the caisson, as well as allowing the doors (one on the caisson,
and one on the aqueduct / basin end) to be reasonably close together when
You can also see the door recesses in this shot from the
So how do you stop the water escaping?
This shot shows both sides of the door and sealing mechanism. Starting in the foreground notice the flush edge around the door which is the facing for the watertight seal to bear on. Also beneath the door there is a hydraulic receptacle where power is transferred to the caisson. To the right of this is the emergency Nitrogen tank which is used should this hydraulic connection system fail.
In the background there is the Aqueduct door. Notice the hydraulic lance used in the aforementioned receptacle to power the caisson whilst docked, as well as the silver pipe work used to fill and empty the water from the void between the two doors.
This image 26th May 2002.
Lets follow the sequence through of undocking the wheel before rotation.
Most of the next images show the mechanisms in operation from the side, taken from the Visitor Centre, with the wheel on the left and the basin on the right (trust me!).
Key elements in this picture are firstly just out of the picture at the top there is clear water from the caisson on the left to the bottom basin on the right.
Centre, the vertical hydraulic piston and cam, this is connected to the door, which is in the open position.
The piston shortens to raise the door.
Immediately below this piston is a diagonal catch which is holding the caisson firmly in place, pulling it towards the wall on the right ensuring a firm and solid bearing surface.
At the bottom of the picture is one of two horizontal pistons, called stow pins, that are locking the wheel in position to prevent it moving. These pins are the a gross fixing method, with the caisson catch ensuring the caisson is firmly in position.
The first operation is to raise the doors, as shown by these two images taken at the Aqueduct seal by the Bridge 19-14 Flotilla on the 23rd May 2002.
Although the hydraulics move both doors together, when they doors clear the water's surface, first the caisson door appears...
Then the Aqueduct door completes.
(23rd May 2002, Bridge 19-40 Society)
Further to these pictures there is a series of 5 pictures of the top gates opening taken by Peter McCulloch on the 1st July.
The same stage in the process but back to the bottom seal. Note the small white/silver hydraulic ram running horizontally at the bottom of the picture, this is holding the watertight seal in place between the basin and caisson.
Next water is pumped out of the void between the doors.
This shot shows the void with the water pumped out.
Note that the watertight seals are still in place, by the
exposed horizontal piston at the bottom of the picture.
Next the watertight seal retracts, with a whoosh as a small quantity of water, not removed by the pumps, drops into the dry well.
The piston is no longer visible and light can be seen through the gap between the caisson and the basin.
Not visible in this shot the Caisson Latch holding the caisson
firmly against the wall on the right is released - the wheel is nearly free to rotate!
Lastly the stow pin seen at the start of this sequence, and the pin on the opposite side of the main arm, at the lower left of this picture retract, allowing the wheel to be free of the basin (and aqueduct structures).
The Stow Pins are small pistons type devices that hold the wheel securely in place.
The wheel is now free to rotate, powered by the hydraulic
motors at the axle.
As the wheel rotates away the full detail of the Basin Door can be seen.
The thick silver pipes pump the water in and out of the void between the doors.
The very thin silver tubes are the hydraulic lines for the rams forcing the watertight seals into place (three off).
The hydraulic lance (copper tipped) is immediately below the
black door. The black caisson latch between the large silver pipes is the mechanism
locking the caisson in place, in addition to the hydraulic stow pins already
discussed that lock the wheel in place.
As the wheel rotates away this wider shot, with the boat in the top left corner shows the full size and depth of the dry well.
This shot shows more clearly the central piston and springs that
apply the watertight seals.
7 minutes later the top of the wheel approaches the bottom, and the whole door and seal process is reversed to allow the passage of the descending boats.
You can read more about the hydraulic motors used to turn the wheel in the Drive Chamber or Experience a trip on the wheel for yourself.
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Unless otherwise stated images are by Peter McCulloch, 1st June 2002.