TM 5-4240-501-14&P
THEORIES OF OPERATION
Carburetion
PULSA- JET CAR BURETORS
Figure 22.
The Pulsa-Jet is a full carburetor incorporating a
diaphragm type fuel pump and a constant level fuel
chamber.
Figure 23.
The fuel tank, the fuel pump and the constant level fuel
chamber serve the same functions as the gravity feed
tank, the float and the float chamber of conventional
"float type" carburetors.
This new design makes it possible to obtain just as much
horsepower from the PulsaJet carburetor as is obtained
from more complex "float type" carburetors. This is due
to the fact that the PulsaJet provides a constant fuel level
directly below the venturi as illustrated in Fig. 23. With
this design, very little fuel "lift" is required to draw
gasoline into the venturi. The venturi can be made
larger, permitting a greater volume of fuel-air mixture to
flow into the engine with a consequent increase in
horsepower.
Figure 23A.
Vacuum created in the carburetor elbow by the intake
stroke of the piston pulls cap A and pump diaphragm B
inward and compresses spring C.
The vacuum thus created on the "cover side" of the
diaphragm pulls gasoline up suction pipe S and under
intake valve D into the pocket created by the diaphragm
moving inward.
Figure 23B.
When engine intake stroke is completed, spring C
pushes plunger A outward. This causes gasoline in the
pocket above the diaphragm to close inlet valve D and
open discharge valve E. The fuel is then pumped into
fuel cup F.
Figure 23C.
On the next intake stroke the cycle is repeated and this
pulsation of the diaphragm keeps the fuel cup full.
Excess fuel flows back into the tank.
The venturi of the carburetor is connected to intake pipe I
which draws gasoline from the fuel cup F.
Since a constant level is maintained in the fuel cup, the
engine gets a constant air-fuel ratio no matter what fuel
level exists in the main tank.
From this point on the carburetor operates and is
adjusted in the same manner as is the Vacu-Jet
carburetor except that the fuel tank does not have to be
half full as in the Vacu-Jet. It can be full or almost empty
and the adjustment will be the same since the fuel level
in the small cup’ is always the same. There are no valve
checks in the fuel pipes. The flaps on the diaphragm
serve as valves.
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