TM 5-4320-218-15
FIELD AND DEPOT MAINTENANCE
Section I. INTRODUCTION
plete disassembly, repair, reassembly of the cen-
75. General
trifugal pump unit and pump engine. Before
Instructions in this section and in succeeding
proceeding with overhaul, check to see that re-
sections of this chapter are published for the
placement parts are available.
use of maintenance personnel responsible for
third and higher echelons of maintenance of the
b. The tools and equipment used for the re-
pump unit. They contain information on main-
pair of the centrifugal pump units and pump
tenance which is beyond the scope of the tools,
engines are those that are normally issued to a
equipment, or supplies normally available to
field and depot shop, and are not enumerated
using orrranizations.
in this section.
76. Procedure
c. Repair parts for field and depot mainte-
nance are listed in TM 5-4320-218-35P.
a. The following sections describe the com-
Section II. ENGINE
(2) Compression stroke. On the compres-
77. Description of Engine Operating
sion stroke, the piston moves upward.
Cycle
Both exhaust and intake valves are
a. General. The four-cycle engine is so term-
closed, and the upward piston motion
ed because of the four distinct and separate
compresses the fuel-air mixture.
strokes of the piston during one complete pow-
er cycle. The engine develops power by rapidly
(3) Power stroke. The power stroke starts
burning a highly compressed mixture of fuel
when the compressed fuel-air mixture
and air in a closed combustion chamber. The
is ignited by a spark from the spark
ignited force of the burned fuel-air mixture is
plug. The ignited mixture drives the
directed against the piston that compressed the
piston downward against the crank-
gas, driving the piston away from the ignition.
shaft to which it is attached by the
The piston is attached to a crankshaft, which
connecting rod. Both the exhaust and
changes the reciprocating motion of the piston
intake valves are closed during this
to a rotary, driving motion.
stroke.
b. Four-stroke action.
(4) Exhaust stroke. During the exhaust
(1) Intake stroke. On the intake, or first
stroke, burned gases resulting during
stroke of the cycle, the piston moves
the power stroke are expelled from
downward; the exhaust valve is clos-
the cylinder. The exhaust valve is
ed, and the intake valve is open. Fuel-
open, and the upward motion of the
air mixture is drawn into the combus-
piston forces the gases through the
tion chamber by the partial vacuum
valve opening to prepare the cylinder
created by the downward piston mo-
for the intake stroke of the next cycle.
tion.
