There are 2 kinds of pressure in the fuel line. There is
static pressure (when the fluid in the line is not moving). When the pressure is set with
no movement, (like when using an electric fuel pump with engine shut off) the pressure will read the same at both gauges. (Assuming both are calibrated exactly the same) Think of the garden hose, if you close the nozzle, you can feel the pressure build in the hose and the pressure is the same thoughout the length of the hose.
Then there is
flow pressure (when the fluid is moving through the line). This is where you will see differences between the gauges. Again assuming that both are calibrated exactly the same. The gauge closest to the pump source will read higher than the gauge farther away from the pump. It's called
friction loss, or loss of pressure due to friction. As the fluid moves through the lines, it loses pressure as it encounters the inside of the lines and bends in the lines. That is why the water department has pump stations all throughout the water system, to overcome this friction loss. There are other factors also. The smaller in diameter the lines, the
more pressure it takes to overcome the friction. In other words, if your have one gauge one a 1/2" line and the next one on a 1/4" line, the
flow pressure will be lower on the 1/4" line gauge. There are a couple of other less important factors also, but these are the biggies...... Hope this helps a little.......
