What would stop freon from flowing into the low pressure port during a needed recharge-the clutch is engaged on the compressor and the max air is on-gauge shows low pressure but freon won't flow?
If the clutch is engaged & turning, there should be no problem getting freon into the system, unless the orifice tube is plugged.
1 : the pressure on a surface at which a flowing fluid is brought to rest in excess of the pressure on it when the fluid is not flowing 2 : the quantity of air measured by most airspeed instruments and equal to the product 1⁄2 ρV2 where ρ is the density of the air and V is the relative speed of the air
There really isn't any statistics. A naturally flowing well must have a well head pressure sufficiently above atmospheric to be able to flow into the separator. A well under natural pressure depletion and flowing conditions will have a declining wellhead pressure, but if artificial lift is installed, the well head pressure can markedly increase.
Does a water meter only measure the time that the water is flowing past it assuming that the water is always flowing at a constant pressure?
No. Most water meters are of the positive displacement type. They meter actual volume, and are pressure independent. Also note that water flow and pressure are not the same thing. You can have high flow with low pressure, and also low flow with high pressure, depending on the size of the pipe and/or openings (such as valves) and the pressure.
Voltage is the force that causes current to flow through a circuit. In a similar way it isn't pressure that flows through a pipe - it is the fluid flowing through a pipe due to a difference in pressure at the entry and exit of the pipe that causes the fluid to flow through, no pressure flowing through a pipe.
Airplane wings, generally, are flat on bottom and curved on top. The reasoning to this is because the wing is curved on top, the air flowing over the wing is forced to move faster than the air flowing under the wing. This causes a lower air pressure above the wing, than the pressure beneath it casing the wing to be pushed to the lower pressure, lifting the wing.