TM 5-3895-359-14&P
Air Inlet Restriction Excessive restriction of the air inlet
plug which is provided for that purpose. If no opening is
will affect the flow of air to the cylinders and result in
provided, drill an 11/32" hole in the exhaust manifold
poor combustion and lack of power. Consequently the
companion flange and tap the hole to accommodate a
restriction must be kept as low as possible considering
1/8" pipe plug.
the size and capacity of the air cleaner. An obstruction
in the air inlet system or dirty or damaged air cleaners
Check the readings obtained at various speeds (at no-
will result in a high blower inlet restriction.
load) with the Engine Operating Conditions on Page 10-
9-1.
Check the air inlet restriction with a water manometer
connected to a fitting in the air inlet ducting located 2"
Air Box Pressure
above the air inlet housing.
When practicability
prevents the insertion of a fitting at this point the
Proper air box pressure is required to maintain sufficient
manometer may be connected to the engine air inlet
air for combustion and scavenging of the burned gases.
housing. The restriction at this point should be checked
Low air box pressure is caused by a high air inlet
at a specific engine speed. Then the air cleaner and
restriction, damaged blower rotors, an air leak from the
ducting should be removed from the air inlet housing
air box (such as leaking end plate gaskets) or a clogged
and the engine again operated at the same speed while
blower air inlet screen. Lack of power or black or grey
noting the manometer reading.
exhaust smoke are indications of low air box pressure.
The difference between the two readings, with and
High air box pressure can be caused by partially
without the air cleaner and ducting, is the actual
plugged cylinder liner ports.
restriction caused by the air cleaner and ducting.
Check the air box pressure with a manometer connected
Check the normal air inlet vacuum at various speeds (at
to an air box drain tube.
no-load) and compare the results with the Engine
Operating Conditions on Page 10-9-1.
Check the readings obtained at various speeds with the
Engine Operating Conditions on Page 10-9-1.
PROPER USE OF MANOMETER
The U-tube manometer is a primary measuring device
Should one column of fluid travel further than the other
indicating pressure or vacuum by the difference in the
column, due to minor variations in the inside
height of two columns of fluid.
Connect the manometer to the source of pressure,
vacuum or differential pressure. When the pressure is
imposed, add the number of inches one column of fluid
travels up to the amount the other column travels down
to obtain the pressure (or vacuum) reading.
The height of a column of mercury is read differently
than that of a column of water. Mercury does not wet
the inside surface; therefore, the top of the column has
a convex meniscus (shape). Water wets the surface
and therefore has a concave meniscus. A mercury
column is read by sighting horizontally between the top
of the convex mercury surface (Fig. 4) and the scale. A
water manometer is read by sighting horizontally
Fig. 4 - Comparison of Column Height for Mercury
between the bottom of the concave water surface and
and Water Manometers
the scale.
10-11-12
