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The majority of evacuation chairs depend on a rotating belt drive
mechanism to span two or more stair nosings. The concept was first
invented by David Egen of Evac+Chair Corporation, USA, who
designed / registered the Egen Polymatic v-belt as a friction braking
device.
Using coefficient of friction the greater the weight of the passenger
the greater is the friction. This friction is increased by adding leverage
to the operator handle. We have found several chair types which
have no friction and therefore no controlled speed of descent.
Other devices require a cable brake and release mechanism.
Virtually all cable brake mechanisms use the “dead man brake”
principle and are either “on” or “off” and do not provide a graduated
increase or decrease of pressure experienced with, say, a bicycle.
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