| Buiding access systems include traction
hoists, which are usually powered by electricity but occasionally powered
by compressed air, incorporated mechanical rope gripping, spring loaded
paws or roller chain that encircle a sheave inside the hoist’s housing.
The wire rope, fitted with a “bullet” end, is fed into the
mechanism, passing between the sheave’s hub and the spring-loaded
chain or paws.
With their “power feeding” of the
wire rope, traction hoists are great for ground rigging. One interesting
feature of a traction hoist is that the greater the load on the wire rope,
the greater the grip exerted on the rope by the roller chain. The drum
hoist, powered by electricity, collects wire on a traditional flanged
drum located under or just behind the stage work area. The support wire
rope has its end clamped off to the flange for protection against the
rope accidentally spooling off the drum. |
