TM 5-4240-501-14&PTHEORIES OF OPERATIONCarburetionPULSA- JET CAR BURETORSFigure 22.The Pulsa-Jet is a full carburetor incorporating adiaphragm type fuel pump and a constant level fuelchamber.Figure 23.The fuel tank, the fuel pump and the constant level fuelchamber serve the same functions as the gravity feedtank, the float and the float chamber of conventional"float type" carburetors.This new design makes it possible to obtain just as muchhorsepower from the PulsaJet carburetor as is obtainedfrom more complex "float type" carburetors. This is dueto the fact that the PulsaJet provides a constant fuel leveldirectly below the venturi as illustrated in Fig. 23. Withthis design, very little fuel "lift" is required to drawgasoline into the venturi. The venturi can be madelarger, permitting a greater volume of fuel-air mixture toflow into the engine with a consequent increase inhorsepower.Figure 23A.Vacuum created in the carburetor elbow by the intakestroke of the piston pulls cap A and pump diaphragm Binward and compresses spring C.The vacuum thus created on the "cover side" of thediaphragm pulls gasoline up suction pipe S and underintake valve D into the pocket created by the diaphragmmoving inward.Figure 23B.When engine intake stroke is completed, spring Cpushes plunger A outward. This causes gasoline in thepocket above the diaphragm to close inlet valve D andopen discharge valve E. The fuel is then pumped intofuel cup F.Figure 23C.On the next intake stroke the cycle is repeated and thispulsation 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 Iwhich draws gasoline from the fuel cup F.Since a constant level is maintained in the fuel cup, theengine gets a constant air-fuel ratio no matter what fuellevel exists in the main tank.From this point on the carburetor operates and isadjusted in the same manner as is the Vacu-Jetcarburetor except that the fuel tank does not have to behalf full as in the Vacu-Jet. It can be full or almost emptyand the adjustment will be the same since the fuel levelin the small cup’ is always the same. There are no valvechecks in the fuel pipes. The flaps on the diaphragmserve as valves.1214
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