Total Head when discharge pipe is above fluid level

[PalomaP]

When pump working between two tanks, and we apply the bernoulli equation, we normaly consider v1 (suction) and v2 (discharge) = 0 (the area of the tanks very big, so velocities will come very small)
However if the discharge pie is above the liquid level in the discharge tank, i should consider the velocity head?

i.e For suction lift pump, suction tank open atmosphera
discharge tank open atmosphera but discharge pipe above the liquid level.
According to Bernoulli,
Htotal= Hatm1-h1-hf1-v1^2/2g+Hatm2+h2-hf2+v2^2/2g
Hatm1=Hatm2
h1= from liquid level of suction tank to centerline pump
hf1=all friction suction side
v1=0
h2= from centerline discharge pipe to centerline pump
hf2=all friction discharge side
v2=???
Should i take the term v2^2/2g as positive?
so, if i take the velocity head in account as positive value I will add v2^2/2g to the total head. However when calculating friction loss as sudden enlargemente at the end of the discharge line, i will add v2^2/2g but in negative (friction loss).
Could someone confirm it?
Thanks a lot

 

[BigInch]

Don't consider the v2 term of the sudden enlargement of the outlet pipe as a velocity head. It is a fitting loss that is (both conveniently and confusingly) proportional to velocity head, but its not a velocity head, per say. Simply calculate the friction loss for sudden enlargement and sum it into the sum of all pipe and fitting and valve losses. Treat the actual outlet velocity at the outlet of the pipe as the v^2/2/g term and then either ignore velocity head completely or include it if you like, as explained in your previous post.

The pump curve showing TOTAL PUMP DIFFERENTIAL HEAD vs FLOW for the pump includes as a small part of the total, the differential change in velocity head from the pump's inlet to the pump's outlet, so the velocity head is already included for you where it is needed (when you consider the pumping element).

So, on the discharge side of the pump, you will be working with a Total Head in all cases, since the manufacturer included it for you in the curve. If you ignored adding the velocity head on the suction side to the pump diff head from the curve, you would be adding pump diff head (both static diff and velocity diff head) to your static suction head (where you might not have included v^2/2/g) and the result would be a total discharge head that is still actually a little bit less (v suction^2/2/g less) than what you really have in the discharge, so you still would be a little conservative.

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