DEFINITION OF TERMS - CONTINUED
Poppet. A spring-loaded ball engaging a notch. A ball
Primary Winding. Low-voltage winding in ignition coil.
Primer. An auxiliary fuel pump operated by hand to feed
Positive. A term designating the point of higher potential
additional fuel into the engine to produce a richer mixture
when the potential difference between two points is
Prismatic Lens. A lens with parallel grooves or flutes
Potential. A characteristic of a point in an electric field or
that deflect and distribute light rays.
circuit indicated by the work necessary to bring a unit
positive charge from infinity; the degree of electrification
Progressive Linkage. Carburetor linkage designed to
as compared to some standard (the earth, for example).
open throttle valves. Primary throttle valves are first
opened and, at a certain throttle position, secondary
The arithmetical difference
valves begin to open.
between two electrical potentials; same as electromotive
force, electrical pressure, or voltage.
Prony Brake. A device using a friction brake to measure
Power. The rate of doing work.
Propane. A petroleum product, sometimes referred to as
Power Booster. A device that increases brake pedal
LP gas, useful as engine fuel.
force on master cylinder during stops.
Propeller Shaft. The driving shaft in the power train that
Power Divider. A mechanism placed between dual rear
carries engine power from the transmission to the
axles to apportion driving effort between the two pairs of
differential; also, the shaft that turns the propeller in
wheels to provide the maximum tractive effort.
Powerplant. The engine or power-producing mechanism
Proportioning Valve. A valve in the brake system that
on the vehicle.
prevents rear wheels from locking during harsh stops.
Power Steering. Vehicle steering by use of hydraulic
Proton. A basic particle of matter having a positive
pressure to multiply the driver's steering effort so as to
electrical charge, normally associated with the nucleus of
improve ease of steering.
Power Stroke. The piston stroke from top dead center to
PSI. Pounds per square inch; a measure of force per
bottom dead center during which the fuel-air mixture
burns and forces the piston down so the engine
PTO. Power takeoff; a location on the transmission or
transfer case from which an operating shaft from another
Power Takeoff. An attachment for connecting the engine
unit can be driven.
to power-driven auxiliary machinery when its use is
Pulsation Damper. A unit used to smooth fuel pulsations
from fuel pump to carburetor.
Preignition. Premature ignition of the fuel-air mixture
being compressed in the cylinder on the compression
Pump. A device that transfers gas or liquid from one
place to another.
Primary Brakeshoe. The brakeshoe installed facing the
Race. The inner or outer ring that provides a contact
front of the vehicle; usually a self-energizing shoe.
surface for balls or rollers to ride on.
Primary Circuit. Low-voltage part of ignition system.
Rack and Pinion Steering. A steering network using a
pinion gear mounted on the end of the