Lock basin empty, you see the threshold on the ground. The Folding Gate is now held
up by the water pressure of the upper water. Its buoyancy tank is already flooded.
The Folding Gate is the gate to the upper water level and is not operated with any mechanics. It can fold up and down freely and contains an air tank. Like a submarine it can be brought up (closed) by forcing air into this tank or it is moved down (opened) by having flooding the tank with water. The latter is happening by itself when the gate is up and the lock basin is half empty. This allows the air to blow out through a "swan-neck pipe" and as the tank is open to the upper water it fills with water. Now it should sink but the upper water holds the gate closed until the lock basin is filled again. Then it automatically sinks to the ground.
<- upper water
The gate lies on the canal bed,
the lock is open,
the tank is filled
Now the gate should sink but the difference in
on both sides lets it stay up until the lock basin is filled with water
again. Then it sinks without any action of the lock master.