Fuel supply systems

A liquid fuel pump arrangement for delivering fuel to an engine comprises a liquid-ring pump including a motor driven bladed impeller rotor which is located eccentrically within a cylindrical bore of a chamber forming part of a hollow pump body structure. The hollow pump body structure also accommodates a motor-driven prime pump impeller which pumps fuel within the pump body structure to an aircraft or other engine. An inner end wall of the liquid ring pump provides the liquid ring with access to the liquid fuel within the pump body structure while an outer end wall of the liquid ring pump has an air/vapor inlet port through which the bladed impeller of the liquid ring pump during rotation thereof draws air/vapor and an air/vapor outlet port the flow of air/vapor expelled therefrom by compression of the air/vapor within the liquid ring in response to rotation of the bladed impeller being restricted by flow restriction means.

This invention relates to fuel supply systems and relates more specifically 
to fuel pump arrangements in such systems for delivering fuel to aircraft 
or other engines. 
Aircraft fuel pumps are often located some distance away from the points 
where they are removing the fuel from the fuel tank, even though the pumps 
may themselves be located within the fuel tank. So-called liquid-ring fuel 
pumps are therefore commonly used in aircraft for removing air/vapour from 
the fuel inlet pipe extending from the fuel tank to the aircraft pump. 
Such liquid-ring pumps include a bladed impeller rotor which is located 
eccentrically within a larger diameter bore of the pump body, so that 
during rotation of the impeller rotor the blade tips thereof come into 
close proximity with the wall of the body bore at one position only. The 
respective ends of the pump body bore containing the bladed impeller may 
be closed by end covers one or both of which support a shaft mounting the 
bladed impeller and which contain suitably located air/vapour inlet and 
outlet ports, respectively. In operation of such pumps, fuel entering the 
pump is centrigued outwards by the rotating impeller and defines a 
liquid-ring which moves concentrically within the pump body bore. Since 
the impeller is eccentric relative to the body bore a crescent-shaped 
cavity forms between the impeller hub and the inner periphery of the 
liquid-ring, this cavity being divided by the blades of the impeller into 
cells of different volume. The crescent-shaped cavity starts to form at 
the point of minimum rotor tip clearance and increases through the first 
180.degree. section which is where the inlet port is located thereby 
allowing air/vapour to be drawn into the pump to fill each cell as it 
expands. Through the other 180.degree. section of the crescent the volume 
of each cell decreases thereby imparting a pumping action which expels the 
air/vapour from the outlet port located in this section of the pump. It 
will be appreciated that sufficient fuel should always be stored in the 
pump at all times in order to maintain the liquid-ring until air/vapour 
has been sucked from the fuel inlet pipe and pump prime achieved with fuel 
then being pumped to the aircraft engines by a further bladed impeller 
usually mounted on the same motor-driven shaft as the ring pump eccentric 
bladed impeller. 
The air/vapour expelled from the liquid-ring pump will usually be fed back 
to the fuel tank. 
These liquid-ring pumps operate satisfactorily until the local pressure 
within the pump drops so that the fuel forming the liquid-ring boils and 
the pumping action of the pump fails due to vapour blockage. 
According to the present invention as broadly conceived a liquid-ring pump 
in an aircraft or other fuel pumping arrangement is arranged to function 
as an air/vapour compressor by restricting the normal air/vapour outlet 
port of the pump. By using the liquid-ring pump as an air/vapour 
compressor the fuel within the liquid-ring will have a higher static 
pressure due to the compressive action of the pump and this higher static 
pressure will prevent the liquid ring from boiling and thereby causing 
failure due to vapour blockage. 
In carrying out the present invention air/vapour drawn into the liquid-ring 
pump, preferably from the fuel tank of an aircraft, through the normal air 
inlet point of the pump is compressed by the pump whilst being expelled 
through the normal air outlet port of the pump due to the restrictive jet 
of a jet pump which provides the suction for drawing and expelling 
air/vapour from the fuel inlet line. The back pressure exerted on the 
liquid-ring raises the static pressure and thereby prevents boiling of the 
liquid-ring. Incoming fuel having air/vapour removed therefrom, is then 
pumped to the aircraft engine by the impeller of a prime pump preferably 
driven by the shaft of the liquid-ring pump.

Referring to the drawing the fuel pumping arrangement illustrated is 
actually located within an aircraft fuel tank 1 and comprises a 
liquid-ring pump 2 arranged to be driven by an electric motor 3 through a 
driving shaft 4 to which a prime pumping impeller 5 is also connected. The 
liquid-ring pump 2 is constructed as already described having a bladed 
impeller 6 mounted eccentrically within a cylindrical pump body bore 7 and 
provides by centrifugal action a liquid fuel ring in response to rotation 
of the impeller. As will be seen from the drawing, however, air/vapour 
inlet 8 to the liquid-ring pump 2 instead of being connected to draw 
air/vapour from a fuel inlet line 9 is connected in the present example to 
draw air/vapour from the fuel tank space above the fuel level 10, but it 
could alternatively be drawn from some other non hazardous source of air. 
The air/vapour drawn into the ring pump 2 is expelled through the normal 
air outlet port 11 of the pump but the flow of expelled air is restricted 
by the jet 12 of a jet pump 13. The restrictive effect of the orifice of 
the jet 12 on the ring pump 2 serves to create a back pressure at the ring 
pump outlet 11 which causes the static pressure of the liquid-ring to be 
raised and thereby prevent boiling of the fuel within the ring pump and 
consequential pump failure due to vapour blockage. The air/vapour expelled 
through the jet 12 of the jet pump 13 causes air/vapour in the fuel 
entering the overall pump 14 through the fuel inlet line 9 to be drawn 
through the pump and exhausted into the fuel tank whilst the air/vapour 
free fuel is pumped to the aircraft engine or engines by the prime pump 
impeller 5 over a fuel outlet line 15. 
As will be appreciated, the air vapour in the fuel inlet line 9 during 
initial fuel lift an engine start up and any air vapour in the fuel, 
especially during boiling of the fuel in the fuel tank 1 which may take 
place at altitudes of about 40,000 feet and above, will be removed by the 
jet pump 13 with the ring pump 2 acting as a compressor rather than a 
suction pump to prevent the liquid fuel ring from boiling whilst driving 
the jet pump with its expelled air/vapour.