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 TM 55-1905-220-14-8
4-7.9.
PRESSURE REGULATOR AND OPERATING CYLINDER - MAINTENANCE
INSTRUCTIONS (Continued).
d. The operating cylinder then holds the throttle valve of the carburetor nearly closed, and the ignition
spark retarded. This is the proper condition for starting. When the engine is started, the operating cylinder
holds engine speed down until the pump is properly primed. In case the pump should lose its prime (as when
the foot valve is lifted from the water allowing air to enter), the engine would tend to race to dangerous speeds.
However, the loss of pressure to the operating cylinder retards the spark, and partially closes the throttle valve,
therefore keeping the engine speed within safe limits.
e. With the regulator set at a given pressure, and the engine running normally, a constant pressure is
maintained on the operating cylinder. The ignition timing, and throttle valve settings remain constant, and the
unit operates in static conditions. Should the input pressure vary, the operating cylinder will take up a new
position, and automatically re-set throttle valve and ignition timing to maintain the regulated pressure.
f. If the pressure regulator allows the discharge water pressure to go above the normal limit or operates
erratically, any of the following may be the cause.
(1) Damaged, lost or plugged orifice disc.
(2) One or both of the bellows of the pressure regulator assembly may be broken. In that case, replace
entire bellows assembly.
(3) The pressure line from the impeller housing to the pressure regulator housing may be closed due to
pinching or kinking.
(4) The pressure regulator cylinder may be fouled with an accumulation of salt, preventing movement
of the spool valve.
g. If the carburetor throttle linkage from the armature plate has become worn or damaged and is
replaced, it may be necessary to reset the throttle position with respect to the armature plate. This is done as
follows:
(1) Move the operating cylinder linkage to the full advance position with 40 psi (275.8 kPa) air
pressure. If air pressure is not available, the spring may be removed from the operating cylinder.
(2) Remove the carburetor instrument panel.
(3) Adjust the rod from the armature plate arm to the cross shaft lever to bring the throttle valve to full
open position (horizontal).
4-232
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