Machinery's Handbook, 31st Edition
PUMPS
2805
Hydraulic Kilowatt In the equations that follow, Q is in l/s; m · is in kg/s; and V
· is in m 3 /s.
h t m · 1000 ------ 9.81 h =
h t Q SG ( ) 1000 ----------- 9.81 =
t V ·
where h t is in meters
SG ( )
=
9.81
KW
∆ pm · 1000 SG ( ) -------------
∆ pQ 1000 ------
∆ pV ·
where D p is in kPa
=
=
=
KW
Wm · 1000 ------
WQ SG ( ) 1000 -----------
WV ·
where W is in J/kg
SG ( )
=
=
=
KW
Hydraulic Horsepower In the equations that follow, Q is in gal/min; m · is in lbm/s; and V
· is in ft 3 /s.
h t V · SG ( ) 8.814 -----------
h t m · g 550 g c -------
h t Q SG ( ) 3956 -----------
where h t is in feet
=
=
=
HP
∆ pV · 3.819 -------
∆ pm · g 238.3 SG ( ) g c ----------------
∆ pQ 1714 ------
where D p is in psi
=
=
=
HP
∆ pV · 550 ------
∆ pm · g 34320 SG ( ) g c -----------------
∆ pQ 246800 ---------
where D p is in psf
=
=
=
HP
WV · SG ( ) 8.814 -----------
Wm · 550 -----
WQ SG ( ) 3956 -----------
where W is in ft-lbf/lbm
=
= =
HP
For centrifugal pumps, a change in impeller diameter or speed results in a change in power according to the affinity laws discussed in Affinity and Similarity on page 2808. Required power for centrifugal pumps is directly proportional to the specific gravity of the liquid being pumped. It is influenced also by viscosity. Pump Efficiency: Pump efficiency is the ratio of the actual power delivered by the pump driver (usually a motor) and the power the pump ideally delivers to the fluid. Losses occur in the system due to friction between the fluid and the pump, as well as friction and/or slip within the pump mechanism. Since hydraulic power is a function of mass flow rate, efficiencies of pumps are often given in terms of flow rate, speed, or specific speed. Drive power to a pump is often called “brake horsepower” (bhp). Pump efficiency is defined by the following equation: η p P hydraulic P brake = ------------ where P hydraulic is the power delivered to the fluid, and P brake is the drive power to the pump. For positive displacement pumps, volumetric efficiency is often used to measure perfor mance. This is the ratio of volumetric flow rate input to displacement per unit time deliv ered by the pump. Torsional efficiency is also commonly used for positive displacement pumps. This is the ratio of actual to ideal torque required to drive the pump. Overall efficiency of a positive displacement pump is the ratio of actual energy delivered, to the input power to the pump.
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