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. |
