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TM 5-685/NAVFAC MO-912
voltmeter switch
watt-hour demand meter
Section II
Alternating current
impulse per cylinder for every four strokes of the
An electric current that is continually varying in
piston. One stroke is one pass through the cylinder.
value and reversing its direction of flow at regular
Fuel filter
intervals. A cycle is one complete set of positive and
Device used to separate solids, impurities, and wa-
negative values of an alternating current. The num-
ter from the fuel.
ber of cycles occurring in one second (cycles per
Gear pump
second or Hertz) is called frequency. Alternating
Delivers fuel from tank to injectors.
current voltage is expressed as volts AC.
Brayton cycle
A mechanism used to control the speed of an engine.
The operating principle by which a gas turbine en-
gine operates, called constant pressure combustion.
Governor characteristics
Charge (circuit breaker)
Terms used in discussion of a governor:
a. Governor sensitivity. Ability to detect a change
The loading or tensioning of circuit breaker springs
in engine speed, expressed as percent of rated top
by compression and/or extension.
Circuit breaker
b. Governor speed droop. Change in engine speed
A device for closing and/or interrupting a circuit
as load increases, expressed as percent of rated
without damage to itself or the equipment it is pro-
tecting when properly applied within its rating. The
c. Governor reset. Adjustment to the governor (in-
interruption feature of this device functions when
ternal or external) which changes the set speed at
an abnormal condition such as an overload or short
any given load point.
circuit occurs. The device usually is set to trip at
d. Isochronous governor. A governor with auto-
125 percent of full load current.
matic reset which compensates for speed droop.
Dew point
Constant engine speed is maintained regardless of
Dew point is the temperature at which dew starts to
e. Governor output. Measure of power the gover-
form (vapor condenses into liquid).
nor can provide to activate the fuel control mecha-
Direct current
nism. Expressed in pounds per inch or pounds per
An electric current that flows continually in one
direction. Direct current voltage is expressed as
volts DC.
Grounding is the connection of a low resistance me-
Electromotive force
tallic conductor between the power distribution sys-
The potential, or voltage, developed by a dynamo or
tem's neutral lead and earth (or an equivalent con-
ducting body). Grounding safely clears line-to-
Emergency power
ground faults.
A power source (held in reserve) that is available for
use in the event of failure of the normal power
A unit of frequency equal to one cycle per second
source. Transfer to and/or from emergency power
(refer to alternating current).
can be automatic or manual.
Fault current
Periodic increase and decrease (oscillation) in
Current flowing to a fault. It may be leakage, a
speed, voltage, or other quantity.
short circuit, or a direct ground.
Four cycle (four stroke) engine
Meters, times, and pressurizes fuel to be delivered
A reciprocating (piston) engine, using gasoline or
diesel oil for fuel. The engine produces one power
to the cylinder.
Glossary 2

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