OP 60.27: Scissor Lift Work Platform Program
There are several distinct types of aerial work platforms, which all have specific features which make them more or less desirable for different applications. The key difference is in the drive mechanism which propels the working platform to the desired location. Most are powered by either hydraulics or possibly pneumatics. The different techniques also reflect in the pricing and availability of each type.
Aerial devices were once exclusively operated by hydraulic pistons, powered by diesel
or gasoline motors on the base unit. Lightweight electrically powered units are
gaining popularity for window-cleaning or other maintenance operations, especially
indoors and in isolated courtyards, where heavier hydraulic equipment cannot be
used. Aerial devices are the closest in appearance to a crane- consisting of a number
of jointed sections, which can be controlled to extend the lift in a number of different
directions, which can often include "up and over" applications.
Scissor lift is a type of platform that can
usually only move vertically. The mechanism to achieve this is the use of linked,
folding supports in a crisscross "X" pattern, known as a pantograph (or scissor
mechanism). The upward motion is achieved by the application of pressure to the
outside of the lowest set of supports, elongating the crossing pattern, and propelling
the work platform vertically. The platform may also have an extending "bridge" to
allow closer access to the work area, because of the inherent limits of vertical-only
movement. The contraction of the scissor action can be hydraulic, pneumatic or mechanical
(via a lead screw or rack and pinion system). Depending on the power system employed
on the lift, it may require no power to enter "descent" mode, but rather a simple
release of hydraulic or pneumatic pressure. This is the main reason that these methods
of powering the lifts are preferred, as it allows a fail-safe option of returning
the platform to the ground by release of a manual valve.