Head

The energy a liquid possesses at a given point or that a pump must supply to move a liquid to a given location. Head is expressed in feet. Any head term can be converted to pressure by using Equation 

p = P x h

Where p = pressure, (lb/ft 2 )
P = density (lb/ft 3 )
h = head (ft)

  1. Cut-off head: the head at which the energy sup- plied by a pump and the energy required to move the liquid to a specified point are equal and no discharge at the desired point will occur.
  2. Friction head : the amount of energy in feet that is necessary to overcome the resistance of flow, which occurs in the pipes and fixtures (i.e., fittings, valves, entrances, and exits) where the liquid is flowing.
  3. Pressure head : the vertical distance a given pressure can raise a liquid. For example, if a liquid has a pressure of 1 lb per square inch, the liquid will rise to a height of 2.31 ft. 
  4. Pump head : the energy in feet that a pump supplies to the fluid. 
  5. Static head : the energy in feet required to move a fluid from the supply tank to the discharge point 
  6. Total head : the total energy in feet required to move a liquid from the supply tank to the discharge point, taking into account the velocity head and the friction head 
  7. Velocity head : the energy in feet required to maintain a given speed in the liquid being moved. If the pump inlet nozzle and discharge nozzle are of equal size, then this term is normally zero.
     Where V = liquid velocity in a pipe G = gravity acceleration, influenced by both altitude and latitude. At sea level and 45° latitude, it is 32.17 ft/sec/sec.
  8. Suction head : the total head in feet on the suc- tion or supply side of the pump when the supply is loaded above the center of the pump. 
  9. Discharge head : the total head in feet on the discharge side of the pump. 
  10. Suction lift : the total head in feet on the suction or supply side of the pump when the supply is located below the center of the pump.
  11. Total differential head : the difference between the discharge head and the suction head, expressed in feet or meters.

Source: Handbook of water and wastewater treatment plant operations

Wikipedia:  https://en.wikipedia.org/wiki/Hydraulic_head