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## Re: [TR] What is the correct way to measure fuel pressure

 To: "'Michael Porter'" , "'Sujit Roy'" , "'Triumphs'" Re: [TR] What is the correct way to measure fuel pressure "Randall" Mon, 21 Oct 2019 21:02:15 -0700 mharc@autox.team.net triumphs@autox.team.net <2E75E051C17D4893B10A381E3652D5BE@RYPC> <4552b246-f8b1-3ea2-18db-ae9f06b4c113@dfn.com> AdWIh/r61Uy0awCSQZWrURkbDM9T5gAA/UEQ SSwn2GiHQa9xwZmcPNwf3Dd+VpANURNQ++qvbkI/O7RAhNuNPm6eHE8hItrwww3tpM5CoEZ8EgTX5bImqm85qjwtTARpiOm76qZnxCwSJUjWvZh85zadZEqY
 ```> Umm, this might confuse a couple of principles.  Yes, lifting > a column of liquid by atmospheric pressure limits the column > to 34 feet (of water, or the equivalent), and the figures > above reflect that for the lower density of gasoline.  But, > the fuel system is not pumping against atmosphere.  It's a > closed system (at least when the float valve is closed), and > with the gauge directly connected to the fuel line, it's > definitely a closed system from pump outlet to gauge.  And, > by definition, the gauge reads PSIG, i.e., pressure above > atmospheric, regardless of ambient air pressure. True, but regardless of whether there is atmosphere on top, the pressure goes down as you get higher along a column. In effect, the weight of the fuel (or whatever) inside the column is sitting on top of the pressure at the bottom, so pressure goes down as you go up. > In a closed system, pressure equalizes at all points in the > system, so, > 2.7 psi at the pump would be 2.7 psi at the gauge. I disagree. If, for example, you set up the system I suggested with a 6' length of pipe, 2 psi at the bottom and no fuel coming out the top; then you plug the top with a pressure gauge, the pressure does not magically increase just because there is a plug there. The gauge still reads 0 psig. Normally, this effect is too small to notice, because we work with much higher pressure in hydraulic systems. 3 or 4 psi in a system that works at hundreds of psi (like a clutch) doesn't make enough difference to notice. -- Randall ** triumphs@autox.team.net ** Archive: http://www.team.net/pipermail/triumphs http://www.team.net/archive tox.team.net ```
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