The Bachmann knot is a friction knot or hitch that uses a carabiner, which functions as a handle, and a thin 6 mm- or 7 mm-diameter piece of cord or a length of tied or sewn webbing like a two-foot sling. The cord is wrapped around a fixed climbing rope and the carabiner, allowing a climber to ascend the fixed rope by sliding a pair of knots up the rope. Usually either three or four wraps of the sling or cord around the rope and carabiner will create sufficient friction to hold the climber's weight and not slip on the rope.
Use Aiders and Locking Carabiners
A set of aiders or slings with steps can be clipped onto the carabiner and will weight the knot when the climber stands in them. It is safer to use a locking carabiner rather than a regular one so that there is no chance that the cord can come out of the carabiner.
How to Use a Bachmann Knot
The Bachmann knot, like the Prusik knot and Klemheist knot, tightly grips the rope when it is weighted or loaded.
When it is unloaded, the knot slides easily up the rope, allowing a climber to ascend the fixed rope. The Bachmann knot is used for ascending fixed ropes; in emergency situations such as self-evacuation from a glacial crevasse; and in a pack-hauling system that uses a pulley.
Bachmann Knot Advantages
A Bachmann Knot is a better friction knot than a Prusik knot to ascend a rope since it is easier to untie after it is weighted. A Prusik knot can lock down on a fixed rope after being weighted and will often become immobile and locked in place. A Bachmann knot is easier to slide up a rope then other friction knots when a climber is wearing gloves. The knot works best on thick ropes--10 mm to 11 mm--rather than thin ropes.
Source About Climbing