German to English Tech/Engineering Mechanics / Mech Engineering mining

I'm translating an operating manual for a "vibration limit switch". This is an sensor with a tuning fork or vibrating element at the tip that is inserted into containers, tanks, pipes, etc. (fluid-containing vessels) to detect the level inside by means of oscillation. Here's a picture: http://www.ferret.com.au/articles/95/0c00f895.asp

The tuning fork or vibrating element emits resonant frequencies that react with the viscous fuild inside the tank. The feedback is measured by the built-in sensor and this signal is converted into level values.

The word above occurs in this sentence: "Gerät an einer Stelle einbauen, an der sich keine
Toträume oder Wächten im Behälter bilden können". It's basically saying that don't install the device in locations inside a tank where dead spaces or *xxx* may form. What the heck are Wächten? The only Web sources I've found seem to describe mountain features! Lookie here for two descriptions and diagrams of Wächten:

http://www.gudelius.homepage.t-online.de/rochf.htm (Wächten)
http://de.wikipedia.org/wiki/Wechte (Wechte)

The "Wechte" (with 'e') may be an alternate spelling so I included it here although the Wikipedia reference above gives me pause since it describes a mountain feature.

Help appreciated,
Marcus