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Appendix — Glossary
control station — a position where controls for unit operation are
located. These positions may include the platform, upper boom tip,
turntable, pedestal or vehicle tailshelf.
control valve — a directional valve controlled by an operator, used to
control the motion or function of an actuator or system.
cooler — a heat exchanger used to remove heat from hydraulic uid.
corner mount — a pedestal mounting position located behind the
rear axle(s) with the centerline of rotation located to one side of the
chassis.
corona ring — see gradient control device.
counterbalance valve — a load holding valve that can be opened
to allow ow in the normally blocked direction by applying hydraulic
pressure to a pilot port, and which contains a relief capability to allow
ow from the blocked direction if the blocked pressure exceeds a
certain value.
courtesy cut — partial cut through limbs so as to allow limbs to fold
towards tree trunks and allow ease of feeding chipper.
cracking pressure — the pressure at which a pressure actuated valve,
such as a relief valve, begins to pass uid.
crazing — a network of ne cracks on or below the berglass surface.
Crazing often occurs when the berglass is struck with a blunt object,
sometimes causing deformation and breakdown of the berglass
resin.
crosstalk — a form of interference in which one circuit or channel
receives some unintentional signal from another.
cross-ported — a hydraulic path connected between the two opposite
ow paths of a hydraulic circuit that allows a route for ow between
the two paths in lieu of ow thru an actuator. To allow sensing of the
pressure in one path by a component installed in the other path.
cSt (centistoke) — a metric unit of kinematic viscosity. In customary
use, equal to the kinematic viscosity of a uid having dynamic viscosity
of one centipose and a density of one gram per cubic centimeter.
curb side — the side of a vehicle which is opposite from oncoming
trafc when the vehicle is traveling forward in the normal direction in
a lane of trafc.
cushion — a device built into a hydraulic cylinder that restricts the ow
of uid at the outlet port to slow the motion of the rod as it reaches
the end of its stroke.
custom option — an option which is not shown on a standard order
form and which requires additional engineering work to supply.
cylinder — a device that converts uid power into linear mechanical
force and motion. It usually consists of a moveable piston and rod, or
plunger, operating within a cylindrical bore.
danger — information that indicates an imminently hazardous situation
which, if not avoided, will result in death or serious injury. This signal
word is to be used in the most extreme situations.
DC pump — a pump which is powered by a direct current electric
motor.
dead band — the area or range near the center rest position of a
hand control where the function does not respond to movement of
the lever or handle.
decal — a thin sheet of exible material which is attached to another
surface by adhesive, and is used to convey instructions, information
and warnings.
deenergize — to remove electrical power from a device, as from the
coil of a solenoid valve.
delivery — the volume of uid discharged by a pump in a given time,
usually expressed in gallons per minute (gpm).
demulsibility — the ability of a liquid to expel another type of liquid.
Commonly used to describe a uid’s ability to cause water to separate
out rather than being held in suspension.
design voltage — the maximum rated line voltage for which an aerial
device has been designed, and for which it can be qualied.
desolve — surface prepping solvent for low voltage coating.
detent — a device for positioning and holding one mechanical part in
relation to another so that the device can be released by force applied
to one of the parts.
diagnostic — relating to the practice of investigation or analysis of the
cause or nature of a condition, situation, or problem.
diagonal brace — the structural member attached near the top of a
corner mount pedestal and extending downward and forward to a point
of attachment on the subbase or vehicle frame between the pedestal
and the vehicle cab.
dial indicator — a meter or gauge with a calibrated circular face and
a spring-loaded plunger, used as a measuring device.
diegrinder — a small, hand held, rotary grinding tool.
dielectric — nonconductive to electrical current.
differential cylinder — any cylinder that has two opposed piston
areas that are not equal.
digger — the mechanism which drives the auger.
digger bail — a tubular housing attached to the gearbox portion of a
digger, which surrounds the motor and provides an attachment point
to the digger link.
digger derrick — a multipurpose, vehicle-mounted device with an
extendible boom which may accommodate components that dig
cylindrical holes, set utility poles, and position materials, apparatus,
and/or personnel.
digger derrick use — the stability criteria for a digger derrick mobile
unit which indicates that the load capacity chart and stability require-
ments apply to the use of the derrick for lifting of loads with the winch
line at the upper boom tip or material handling jib tip, with the platform
stowed or removed, if so equipped.
digger hanger bracket — the structural member on a digger derrick
which supports the digger link on the extendible boom.
digger latch mechanism — a mechanism which secures the digger
to the lower boom when it is stowed and to the extendible boom when
it is unstowed.
digger link — the structural member which attaches the digger to the
digger hanger bracket.
digger/winch valve — the control valve on a digger derrick that
directs hydraulic pressure and ow to the digger and winch hydraulic
circuits.
digital signal — an electrical signal that communicates information
by the use of two distinct levels of voltage or current, a high “on” level
and a low “off” level, which are sent in a series of pulses. The timing
of the pulses is used to indicate the level of an input parameter such
as control lever position, or information such as the address setting of
a radio control transmitter linking it to its receiver.
diode — an electrical component that allows current ow in one direc-
tion but not in the reverse direction.
directional valve — a valve that selectively directs or prevents uid
ow through desired passages.
disc — the rotating component, housing the knifes on a disc chip-
per.
disc chipper — a wood chipper which utilizes a disc shaped, rotating
cutter mechanism.
disc housing — weldment housing the cutting disc, comprising of the
base, stationary hood and access hood.
discharge chute — directs chip discharge from the cutter mechanism
in the desired direction.
displacement — the quantity of uid that can pass through a pump,
motor or cylinder in a si ngle revolution or stroke.
docking station — a device used to mount a remote control transmit-
ter on a platform.
dog clutch — see drum clutch.
double-acting cylinder — a cylinder in which uid pressure can be
applied to either side of the piston to move the rod in either direction.
double elevator — an elevator lift with two load carrying arms. The
double elevator system includes a lower pedestal, lower arm, lower arm
cylinder(s), riser, upper arm, upper arm cylinder(s), and upper pedestal,
plus parallel links in both the lower and upper sections.
double-pole, double-throw (DPDT) switch — a six-terminal electrical
switch or relay that connects, at the same time, one pair of terminals
to either of two other pairs of terminals.
double-pole, single-throw (DPST) switch — a four-terminal electrical
switch or relay that, at the same time, opens or closes two separate
circuits or both sides of the same circuit.
down load — the downward force created when an external force is ex-
erted on the boom, such as a winch pulling cable on a cable placer.
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