Product Manual

6
6.0 Glossary
Creep speed: Slow, constant, fixed rate of motion
of a hoist.
Duty cycle: The amount of work a hoist can
perform in a given period of time, generally
measured by maximum run time and number of
starts within that period. Duty cycle ratings are
designated H1 through H5.
Duty class: Identifies the type of service for which
a hoist is designed, designated A through F.
Headroom: Minimum distance between saddle of
top hook to saddle of load hook, measured when
load hook is at upper travel limit. Smaller
headroom allows a hoist to fit in tighter work
spaces.
Hook saddle: The inside arc of the hook which
contacts the beam (top hook) or where the load
sling is seated (load hook).
Toggle or “bump fire”: Rapid press and release
of a control button to raise or lower load in
intermittent steps. (A variable frequency drive in
lowest speed range often eliminates the need for
toggling.)
Overtravel limit device: A device for limiting
upward or downward travel of the load hook at the
extremities of its lift. (If activation of the device
alters the electrical circuit within the machine, it is
often called a “limit switch.”)
Load block: The assembly of hook or shackle,
swivel, bearing, pins, sheaves and frame
suspended by the chain.
Magnetic disc brake: A stopping device controlled
by the application of electrical current to the coil of
an electromagnet, which draws away an armature
allowing rotation of the shaft. When the magnet is
de-energized, the armature moves back toward the
brake face and squeezes together friction discs –
the torque is applied to the hub and stops shaft
rotation.
Overload limit device: A mechanical or electrical
device that prevents the hoist from lifting when
excessive load is applied.
Rated Load, or Capacity: The maximum load
weight, usually labeled as tonnage, which the hoist
is designed to handle as designated by the
manufacturer.
Reeving: The system in which a chain or rope
travels around a running sheave.
Running Sheave: A sheave which engages the
chain/rope and rotates as the load block is raised
or lowered. Also called “load sheave” or “load
sprocket.”
Variable frequency drive (“inverter”): A control
system that converts fixed line voltage and
frequency into a three-phase system with infinitely
variable voltage and frequency, in order to regulate
motor speed.