The Folding Gate
The gate to the upper level water. Here it is open, so it lies on the ground under water.

"Donnerschleuse" in Neu-Lankau. The "upper water" of the lock, highest level in the whole canal. It leads to Witzeeze, via Moelln (lake with a port).

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 (UW)          lock basin->
The gate lies on the canal bed,
the lock is open,
the tank is filled
with air

<- upper water (UW)
The gate becomes less dense than water
and rises,
it folds up and closes.

<- upper water (UW)
The gate is closed, the lock basin is emptied,
the water pressure at the "swan-neck pipe" disappears
and the air escapes.
Water fills the tank.

Now the gate should sink but the difference in pressure 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.