Friction head positive or negative?

[PEinOHIO]

in my reference book (MERM book, page 18-6), they are analyzing a pipe system and show the friciton head on the suction side of a pump as negative (this makes sense to me, since the friction is taking some of the head away from the fluid). but on the discharge side, they show the friction head as positive. this is confusing to me, especially since they then find the total head added by the pump, which is discharge head minus suction head, which gives you positive frition heads for both the suction and dicharge side. can someone clarify?

 

[IRstuff]

postive_head - negative_head = 2 * positive_head

TTFN

FAQ731-376

 

[DLite30]

Think about the total head the pump needs to provide including the head loss due to flow losses on the suction side and the discharge side in able to get the desired pressure at the end of the line.

TDH = discharge head + discharge loss - suction head - suction loss.

You also have to be concious of where in the system the head values are taken (either at the pump or at the ends of the lines).

 

[BigInch]

Hydraulic calculation usually reduces to finding either the head available at some downstream point, or the head required at some upstream point. Friction head always reduces the downstream head available and always increases the upstream head required. Use the appropriate sign to make that statement true for whichever side of the equation friction happens to appear.


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