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HEAD OF WATER -- vertical depth of water measured in feet or in pressure per unit or area. In
hydraulics, head always represents pressure and it is expressed interchangeably in feet of
water or pounds per square inch and sometimes in inches of depth of mercury.
STATIC HEAD -- the pressure that is exerted by a stationary column of water of a given height
or depth.
TOTAL HEAD OR TOTAL DYNAMIC HEAD -- the maximum height above the source of supply
to which the pump would elevate the water plus all the resistance to flow in the pipe or hose
line.
DISCHARGE HEAD -- the pressure measured at the discharge outlet of a pump.
SUCTION HEAD -- the positive pressure measured at the suction entrance of a pump (when
pumping from an elevated tank or hydrant).
VELOCITY HEAD -- the equivalent pressure represented by fluid in motion as measured by
means of a Pitot Gage.
STATIC LIFT -- the vertical height of the center of the pump above the source of supply (when
pump from draft).
TOTAL SUCTION LIFT -- the static lift plus the friction in suction line plus entrance losses.
NET PUMP PRESSURE -- the total dynamic head of the pump.
EFFECTIVE NOZZLE PRESSURE -- the pump discharge pressure minus hose friction plus or
minus the difference in elevation above or below pump.
WATER HORSEPOWER - the theoretical power required to deliver a given quantity of water
per minute against a given head.
BRAKE HORSEPOWER -- Actual power as delivered by a motor or engine to a driven
machine.
PUMP EFFICIENCY -- The quotient of the water horsepower divided by brake horsepower
required to produce it.
WATER HAMMER -- a series of shock waves produced in a pipeline or pump by a sudden
change in water velocity. A sudden change in flow velocity can result from rapid closure of
valves. A pressure wave is set up which travels back and forth in the water column at
extremely high speed producing rapid vibrations that may be violent and destructive if the
water column is long.
THE MAXIMUM THEORETICAL LIFT of a pump is 34 feet, which is the pressure of the
atmosphere at sea level. The maximum practical total lift at sea level is 20 to 25 feet
(depending on the type and condition of the pump) and this decreases with drops in
barometric pressure.
Prepared by: EAP
Approved by: MCR
DEFINITIONS
1
Rev. #:1
Date: 1/29/07
1200510
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