1)
A
pneumatic
governor, for governing
of
its speed, consist
of
diaphragm block
in
fuel injection
pump
and
of
Venturi unit
in
inlet manifold, which are
connected
together
with an air pipe.
2)
Now, following
the
scheme and diagram
of
operation principle, we will briefly
explain
how
this governor operates. When intake air passes through Venturi
that
closes inlet manifold
to
some
extent,
its flow velocity rises
but
at
the same
time, static pressure
at
that
part
(to
be taken through pipe
that
opens
to
its
flow direction
at
a right angle) falls considerably below
the
pressure
on
the area
free from
the
inflow
of
air (generally, atmospheric pressure)
or
in short, turns
into negative. This negative pressure rises,
as
can be seen
in
Fig. 3·25, with the
rise
of
engine speed and consequently
of
flow velocity of intake air. Through
an air pipe,
it
is conducted into negative pressure chamber in diaphragm block
to
work
on
diaphragm.
The
governing force it produces
is
calculated:
(Venturi negative pressure)x(Diaphragm area)=(Governing force)
Main
sprinC
Diff.,.
...
ti
..
~.
~
both
sides
of
di'-'ecm
by
Yenlui
necativo
Pr_L
Openi"l
in idlinl
.:tian
r..,~.~~:::t=====t=:j===:;~=;;~::;'"
Fig.
3·25
Diagramatized principle
of
pneumatic governor operation
Now suppose
that
max. engine speed needs
to
be
governed
at
A (rlp.m.). While,
with
Venturi butterfly valve opened 100%, main spring with setting load
equivalent
to
governing force Fc
that
is
produced by negative pressure C
at
point
B
on
Venturi negative curve (Fig. 3·25)
is
placed on diaphragm. When the
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29-
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