PROPER USE OF MANOMETER
PRESSURE CONVERSION CHART
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. 2) and the
Fig. 2 - Comparison of Column Height for
scale. A water manometer is read by sighting
horizontally between the bottom of the concave water
surface and the scale.
The U-tube manometer is a primary measuring device
indicating pressure or vacuum by the difference in the
Should one column of fluid travel further than the
height of two columns of fluid.
other column, due to minor variations in the inside
diameter of the tube or to the pressure imposed, the
Connect the manometer to the source of pressure,
accuracy of the reading obtained is not impaired.
vacuum or differential pressure. When the pressure is
imposed, add the number of inches one column of
Refer to Table 7 to convert manometer readings into
fluid travels up to the amount the other column travels
down to obtain the pressure (or vacuum) reading.
other units of measurement.
ENGINE ELECTRICAL GENERATING SYSTEM
condition usually indicates the voltage regulator is set
Whenever trouble is indicated in the engine electrical
too high or is not limiting the alternator output. A
generating system, the following quick checks can be
made to assist in localizing the cause.
high charging rate to a fully charged battery will
damage the battery and other electrical components.
A fully charged battery and low charging rate
A low battery and low or no charging rate condition
indicates normal alternator-regulator operation.
could be caused by: Loose connections or damaged
wiring, defective battery or alternator, or defective
A low battery and high charging rate indicates normal
regulator or improper regulator setting.
Contact an authorized Detroit Diesel Allison Service
A fully charged battery and high charging rate
Outlet if more information is needed.