"The hydraulic lift n° 4" Strépy-Bracquegnies Things to Do Tip by cadzand
Strépy-Bracquegnies Things to Do: 7 reviews and 7 photos
It is also part of the Unesco World Heritage monuments.
How does it work ?
These lift-locks consists of a pair of tanks, each as large as a conventional lock chamber and closed at each end by a "guillotine" gate. The adjacent ends of the upper and lower pounds of the canal are fitted with similar guillotine gates such that when the tank is clamped to either of them, which seals the sides and bottom of the gap between the gates, and the water levels in the tank and gap have been equalised with that in the pound, the gates can be raised together. Each tank is supported by a central column which acts like a piston in a deep vertical cylinder filled with water at high pressure, linked with that under the other column through a pipe with a valve that can be opened and closed as required. The total volume of water at high pressure is kept constant at the quantity needed to ensure that when the lower tank is correctly aligned for opening the gates from the lower pound, then the upper tank is similarly at just the right height for opening the gates from the upper pound.
As the total volume of water displaced by any vessel entering the tank has exactly the same mass as that vessel, the two tanks remain in equilibrium so long as the depth of water in them is the same. Once the tanks have been loaded, the gates are dropped, the clamps released and enough water to reduce the surface level by about 30 cm is let out from the lower tank into the pit underneath (from which it drains away through a pipe laid beneath the lower pound). When the valve in the connecting pipe is opened, the unbalance is sufficient to make the upper tank descend to the lower level, thus raising the other tank to the position where it can be clamped to the upper pound; the valve is then closed. As the water level in the upper tank is now about 30 cm below that in the upper pound, water must be allowed to flow from it into this tank until the levels are equal. Then the guillotine gates can be opened and the cycle repeated.
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