HGL vs EGL

[GoldDredger]

I am trying to recalculate the HGL of a simple run of pipe after adding 3 more cfs into the system that it wasn't originally designed for. (Original design used wrong C factor in rational formula) I have a known elevation of the HGL and velocity at any given point along the stretch of pipe.

We know that the EGL = HGL + velocity head ((V)(V)/2g).

If I start at a point where the HGL is known, lets say it's 2-ft above the crown of the pipe. I also know the velocity at this point, say 5 ft/s. So in calculating the EGL = 2-ft + (5)(5)/2g = 2.38 ft.

Now if we introduce an additional 3 cfs into the pipe, the new velocity through the pipe increases, (v=q/a) which makes the velocity head also increase.

Subtracting the new velocity head from the calculated EGL, the new HGL is lower than the old HGL.

So there must be something wrong with my approach. Adding more fluid into the system couldn't lower the HGL, it would have to raise it.

What am I doing wrong here?

Maybe by adding the 3 cfs and increasing velocity, I also add to the frictional losses that determine the HGL in the first place. So while the velocity head grows, so does the frictional loss. Making the overall HGL rise?

 

[cvg]

yes

 

[elev8848]

You must have realized it already.
Assuming additional 3 cfs flowing through the same pipe means you (unknowingly) changed both the HGL and EGL.
So you just start again from scratch. Re-calculate both HGL, velocity and EGL.
Thanks