Pumps, Fans and Turbines - Horsepower

[Esam]

[h=Definition of British Horse Power for pumps, fans and turbines - how to convert to other common units]2[/h]Horsepower Horsepower is the imperial (British) unit of power. A horsepower is the ability to do work at the rate of

• 33,000 ft.lb per min or
• 550 ft.lb per second

Note that Power is "Work per unit time" and work is "Force through distance". In gravity systems Force is Weight - mass multiplied with gravity.
The total horsepower developed by water falling from a given height is the product of the mass flow rate in pounds per minute times the falling height in feet divided by 33,000. It can be expressed as:

P_hp = m_min h g / 33000 (1)
where

P_hp = power (horsepower, hp)

m_min = mass flow rate per minute (lb_m/min)
h = head or height (ft)

g = acceleration of gravity (32 ft/s²)

(1) can alternatively be expressed as:

P_hp = m_sec h g / 550 (1b)
where
m_sec = mass flow rate per second (lb_m/s)

(1) can also be expressed as:

P_hp = γ Q h / 33000 (1c)
where
Q = volume flow rate (ft³/min)

γ = specific weight (lb_f/ft³) (weight is force)

[h=Water Horsepower for Flow in gal/min]4[/h] Water horsepower for flow in gal/min can be expressed as:

P_whp = SG Q_gal h / 3960 (1d)
where
Q = volume flow rate (gpm)
SG = specific gravity

h = head (ft)