Flow through a venturi meter (TEL)

[SherlockOhms]

Homework Statement

I recently completed an experiment which analysed flow through a venturi meter. We were then asked to plot the total energy line, velocity head line and pressure head line across 11 piezometers connected to the pipeline.

Homework Equations

$\frac{P_1}{\rho g} + z_1 + \frac{v^2_1}{2g} = \frac{P_2}{\rho g} + z_2 + \frac{v^2_2}{2g}$

The Attempt at a Solution

Seeing as $z_1 \approx z_2$, they can be neglected. My problem is, that when plotting the TEL it decreases, then increases a bit before finishing at a point lower than it's initial height. I know that it should decrease along the flow and never increase. Does it make any sense that i's behaving this way? The dynamic head and pressure head lines behave as expected. The pressure head line decreases to a min at the throat and increases again to a point lower than it's initial point. The velocity head line increases to a max at the throat and then decreases to a min. So, both the velocity head and pressure head lines make sense, but not the TEL. I've been calculating the total head using: $$\frac{P}{\rho g} + \frac{v^2}{2g}$$ ignoring $z$ seeing as it won't make a difference when looking at the changes in the TEL. $$Pressure Head: \frac{P}{\rho g}$$
This is read from the piezometer. Velocity Head: $$\frac{v^2}{2g}$$ This was calculated using the areas given on the venturi meter itself and the measured flow rate, to get the velocity. g is a constant. So, am I doing anything wrong or is this just down to experimental error?

 

[SherlockOhms]

This is a rough sketch of what the lines look like.

 

[SherlockOhms]

Bump.