ENGINE OVERHAUL

The difference between the two readings, with and without the air cleaner and ducting, is the actual restriction

caused by the air cleaner and ducting. Check the normal air inlet vacuum at various speeds (at no-load) and

compare the results with the *Engine Operating Conditions Specifications*. PROPER USE OF MANOMETER

The U-tube manometer is a primary measuring device indicating pressure or vacuum by the difference in the

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. 2) and the scale. A water manometer is read by sighting horizontally between

the bottom of the concave water surface and the scale.

Should one column of fluid travel further than the other column, due to minor variations in the inside diameter

of the tube or to the pressure imposed, the accuracy of the reading obtained is not impaired.

Refer to Table 3 to convert the manometer reading into other units of measurement.

1 inch water

=

0.0735 inches of

mercury

1 inch water

=

0.0361 psi

1 inch mercury =

13.6000 inches of

water

1 inch mercury =

0.4910 psi

1 psi

=

27.7000 inches of

water

1 psi

=

2.0360 inches of

mercury

1 psi

=

6.895 kPa

1 kPa

=

0.145 psi

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