......you sure you got that right Noel......

Yes

Lazy answer, no cookie for you...

Pat, you were entirely correct, I was being lazy, having re-read your post it’s obvious you’ve put a lot of time into it and the cocky tone of it demands a response.

As I said, I wrote a reply on the night but thought better of posting it, below is an edited version of that.

You said this….

A 33ft column of water is one atm, or 14.7 psi, one foot height of water generates a pressure of 14.7/33, or 0.44 psi pressure.

….and that's wrong. Not the arithmetic, but how you apply it.

You say that if a 33ft column of water exerts pressure of 14.7 psi, therefore 1/33 of that height will exert 1/33 of the pressure, being 0.44psi. So, by that reasoning, if you removed the last foot of water, atmospheric pressure becomes zero at sea level, where did the 14.7psi disappear to? If this was the case planes couldn't get off the ground and toilets wouldn't flush. You agree that 14.7 psi is atmospheric pressure at sea level on one hand then set about disproving it on the other.

Atmospheric pressure is caused by gravity but doesn't act like it, it’s inescapable, non-selective, multi directional. For the purpose of this discussion, it’s everywhere, from oil tankers to fuel bowls. Perhaps if you visualise it as placing an object underwater it’s easier to understand.

The mistakes you made were not understanding the reference to the column of water, confusing zero with absolute zero (The “zero” used for measuring and to which instruments and gauges are set is actually 14.7 psi), the relationship between gravity and pressure, doubling up on the arithmetic, suggesting that different objects are subject to different amounts of pressure, for example, you say pressure on the outside of the fuel line at 5000ft is 12.2 psi yet the pressure inside the line is 0.09! You don’t seem to grasp that pressure is the same everywhere. Then there’s the weird premise that atmospheric pressure at sea level is actually 33’ above it and the mish mash of calculations that flowed from it, and finally, throwing in a few red herrings, like flow rate, flow resistance and altitude that have nothing to do with anything in the context of this discussion.

Certainly head pressure changes depending how full the tank is but the minimum can't be less than 14.7, that is the starting point with the lowest possible fuel level!

You calculated the fuel line pressure (which is open to the atmosphere and is the same as in the bowl) of a gravity fed FJ fuel system to be somewhere around 0.01psi, if that were so, by what action does fuel get from the carby to the cylinder?

A: Bernoulli’s principle

B: Pat’s principle

C: Atmospheric pressure

D: The sucking principle

So Pat, just answer me that one question above about how fuel gets to the cylinder. If you can answer that (and understand it), the flaw in your calculations will become glaringly and instantly obvious.

Noel