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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS. 



TBCHNIGA1 MEMOKAHOUM. l o1 



FAKIR FUEL PUMP. 



j?Tom "Dei- Kotorwagen," 
December 30, 1931. 



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June, 1022. 



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FAKIR Ftfct PUMP. 

In designing the Fakir fuel pump* the fundamental idea was 
to obtain a simple and reliable method of conveying the fuel 
from a low tank to the carburetor, with the avoidance of the 
faults of all former methods and the simultaneous warming of the 
fuel by means of the heat of compression generated. 

The principle of the Fakir fuel pump rests on the well-known 
principle of the diaphragm pump, which must however be suitably 
adapted to the present purpose* Figs. 1 and 3 are drawings of 
the pump. Inside the housing (formed by the circular wall A, 
the front wall A x , and the rear wall A ? ) , there is a hollow body 
Q cast in one piece with walls A and A x > containing the inter- 
connected horizontal and a vertical channel Q a and Q 3 . The chan- 
nel Qi is open toward the diaphragm and contains the spring K 
which presses against the diaphragm. The channel Q 3 is con- 
nected with the inlet D 1 and above into the pump housing. The 
intake valve' F and the pressure valve G are respectively be- 
low and above the channel Q x . The seats of these valves are 
shaped out of the tube connections F x and 1 which communicate 
with the channel Q 3 . The hollow body Q also contains a second 
horizontal channel Q 3i which lies below the intake valve F 
and forms a connection between the vertical channel Q 2 and the 
space inside the pump housing through the return valve P (for 
the back flow). The latter is held shut by a spring p 2 which 
* From "Der Motorwagen, rr December 20 3 1921, pp. 779-780/ 



is coiled about a bolt S. The bolt and spring lie in a cross 
bore F 3 of the tube F a . The bolt S is screwed into the wal.l 
A and its outer end is covered by a screw cap S r Below the 
return valve, there is a non-return or check valve T which, like 
the inlet valve, is provided with a strainer to keep out any dirt 
there may be in the fuel* The diaphragm lies between the wall A 
and the cover J which is clamped on to a special shaped base. 
This base, which is formed by the wall A x , is so made that the 
diaphragm, can only yield within suitable limits, without danger 
of rupture or fatigue, and is then supported by the 'base so that 
the high cylinder pressure cannot hurt it. The distance of oscil- 
lation in either direction and the pressure of the diaphragm 
spring have been adjusted by many experiments, so as to come with- 
in the limits of elasticity of the metal diaphragm and prevent the 
possibility of fatigue. For the protection of the diaphragm from 
the spring, there is a pressure plate on the end of the latter. 
The gas-pressure space, inclosed between the diaphragm and the 
cover, is (through the elbow M 2 and the channel M 4: , which op- 
ens into the gas space through the cross channel M s ) in direct 
communication with the engine cylinder. 

The Fakir fuel pump operates as follows: The pressure varia- 
tions in the engine cylinder produce oscillations of the diaphragm. 
During the period of diminished pressure in the engine cylinder, 
the oscillation of the diaphragm (supported by the force of the 
spring behind it) draws fuel from the tank, which is then (during 



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the period Of compression, explosion and exhaust) driven out 
again. This process, which is continuously repeated all the time 
the engine is running, pumps considerably more fuel than the en- 
gine requires. The excess fuel must therefore be rendered harm- 
less, This is accomplished by the automatic flow of the excess 
fuel (which does not run through the outlet E 1 to the carbure- 
tor) back through the return valve P into the fuel column under 
the intake valve F. In order to prevent this action from caus- 
ing any return flow of the fuel column into the fuel tank, the 
check valve T is introduced. The pump therefore always deliv- 
ers to the carburetor only the quantity of fuel required at the 
time by the engine , while the excess fuel circulates inside the 
pump. Now, since heat is produced by compression, this circulat- 
ing fuel is highly heated by coming in contact with the thin met- 
al diaphragm. The fuel is still further heated by the heat con- 
duction of the metal pipe connecting the pump with the engine 
cylinder, in which pipe hot gases, oil and other fluid residues 
of the explosions oscillate to and fro. After the engine has 
been running a short time, these fluid residues fill up the gas 
space (between the diaphragm and cover J) and parts of the deliv- 
ery pipe, so that, in practice, no increase in the volume of the 
clearance space takes place in the engine. By suitably adjusting 
the size and length of the delivery tube from the pump to the en- 
gine cylinder, it is possible (within certain limits) to give the 
fuel any desired amount of preliminary heating and, even for low 



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initial temperatures of the fuel in the tank, obtain final temper- 
atures of 30~35°G in the float chamber of the carburetor. Exper- 
ience has shown' that engines with fuel warmed in this manner can 
use cold air even in winter and 'still develop a high degree of 
efficiency, as well as be able to utilize difficultly volatile 
fuel* 

The Fakir fuel pump can be installed anywhere between the 
fuel' tank and the carburetor, since the flow of fuel to the pump 
does not depend on gravity, but on adjustable pressure. It may 
be further said that it is proof against all shock's and changes of 
inclination on motor vehicles of all kinds (including water and 
air craft) , since it has no movable parts aside from the four 
valve balls which are held by springs. The chances of its getting 
out of order are therefore reduced to a minimum. It requires no 
attention, aside from seeing that the piping is tight, which is 
an essential condition for any pump. 

Translated by the National Advisory Committee for Aeronautics. 




Section A-A 



FAKIR FUEL PUMP