Belaying A Raising System; Mirrored Systems - CMC Rescue MPD User Manual

BELAYING A RAISING SYSTEM

If the load is being raised, then the Belay Line can simply be pulled hand
over hand through the MPD. However, if the distance the load has to be
raised is greater than approximately 30 m (100 ft), it is recommended to
convert the Belay Line system into a simple 3:1 mechanical advantage
pulley system to assist with the raising of the load. The load can be raised
more efficiently if the Belay Line assists with the raising, since it is possible
that a lower mechanical advantage will be required by the Main Line. This
will also take the stretch out of the line. For the final edge transition, convert
back to a 1:1 system using only hand tight tension on the Belay Line by
pulling it hand over hand through the MPD.

MIRRORED SYSTEMS

Rope rescue systems, where both rope systems are capable of
simultaneously performing as a Main Line and a Belay Line are referred
to as Mirrored Systems. Unlike the MPD, most descent control devices
are incapable of performing both functions concurrently. Ideally, a true
independent Mirrored System is achieved with maximum flexibility and
versatility when both the Main Line and Belay Line are each managed
with an MPD. This way either rope system can perform either function,
without the need for complex changeovers or function specific equipment.
Additionally, if an MPD is used for both the Main Line and Belay Line in a
Shared Tension System, then should either of these systems fail, the other
rope system can serve as a belay and the potential arresting distance is
minimized since both ropes will be prestretched.
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