If the oil level in the tank is 4' below the fuel unit and 10' away, what is the approximate vacuum?

To determine the approximate vacuum created when oil is drawn from a tank located 4' below the fuel unit and 10' away, it's essential to understand the principles of fluid dynamics and the factors affecting the vacuum.

When oil is drawn from a tank located below the fuel unit, gravity works against the pump, creating a vacuum in the fuel line as the pump tries to lift the liquid. The height of the oil level creates a pressure difference, and in this case, a height of 4' translates to a specific measurement of vacuum.

The general rule is that for every foot of elevation change in a liquid fluid, there is approximately 1 inch of mercury (inHg) vacuum created. Given that the tank is 4 feet below the fuel unit, this can directly relate to a vacuum measurement using the conversion that roughly equals 4 inches of mercury. However, since there is also a horizontal distance of 10', and friction loss in the line must be accounted for, it adds more complexity.

In practice, the summed effect of vertical drop and horizontal distance leads to a need to approximate the theoretical vacuum considering both the height and some internal resistance to flow due to the horizontal run. This often results in the need to consider a slightly higher vacuum