Fuel Pressure Gauge instead of Fuel Level?

So here's my dumb question for the week guys :huh:

When old time race cars (and perhaps even modern ones, I don't know, or planes for that matter), use fuel pressure rather than fuel level, how does this work? I mean how do you interpret the information?

At what point in pressure drop do you run out of fuel, Zero? How do you gauge at any particular time how much pressure equals how many miles you have left?

Also, as I am about to start the gauge installation, and the original P4 had a fuel pressure gauge (and as I would like to stay as per original), what are the benefits of the pressure gauge over more normal fuel level gauges?

One idea I did have was to replicate the face of a pressure gauge, but have the dial actually give level readings. I suppose the needle at the far left reports empty either way?

PS. Next time I'll try use less words to get my point across!

TIA

Mark

Both my race cars, the T70 and Z, have fuel pressure gauges. But it isn't for fuel level, it is diagnostic tool. Fluctuating fuel pressure can alert you to problems in a variety or situations and noting where/when the pressure fluctuates can be a great help in solving the problem.

Aha, so it's nothing to do with range then. The technicians know how many laps x amount of fuel should do and time their stops accordingly? I was thinking that x pounds of fuel pressure meant x amount of fuel in the system.

If that's the case I will stick with plan A and make a fuel level gauge look like a pressure gauge.

Thanks for the explanation Ron.

Fuel pressure could in theory be used for level measurement, If a pressure transmitter was connected to the bottom of the tank then the hydrostatic pressure exerted on the transmitter would be linear to the fuel quantity in the tank ( assuming the shape was linear) , This type of level measurement it used a lot in industry but generally with a vessel which has a far larger head of material 2-3 Meters upwards.

So in theory you are correct but in reality would not be very accurate in this type of installation.

Hope this helps.

Aircraft use densitometers in the fuel tanks to give level, and fuel flow measurements to give an indication of usage. Fuel pressure is only used to give an indication of fuel pressure leaving the pump, that way we know which pumps are producing the correct pressure and which ones are not. However, on most aircraft this is not a pressure reading but rather like the oil light in your car, if it turns yellow its bust.

Hi all

Mark

Well, on my car are two tanks and two pumps.
One left, one rigth.
So the main pump is on the left side.
If the needle of the pressure gauge is moving downwards, so i switch off the left pump and switch on the rigth pump. Now its time to refuel. Very easy and every time some liters of reserve fuel in the tank. Had no problems with this .

Cheers

Mike S.