در رابطه فوق راندمان موتور نیز باید منظور شود. علاوه بر آن راندمان پمپ فاکتور ثابتی نیست و در صورت تک سرعته بودن، راندمان ماکزیمم تنها در آن سرعت اتفاق می افتد.
Hydraulic Work Done (kW) = Pu = (ρgQH) / 1000
ρ = density (kg/m³)
g = gravitational constant = 9.81 (m/s²)
Q = volumetric flow rate (m3/s)
H = Total head rise across the pump (m)
Input power to pump shaft: -
Pp = ρgQH / ηp
ηp = pump efficiency
Input power to motor: -
Pgr = ρgQH / ηp ηm
ηm = motor efficiency
A fixed speed pump can only operate at head/flow combinations described by its pump curve. The pump curve is a characteristic of the pump.
A pumping main or system has a series of possible head/flow combinations described by its system curve. The system curve is a characteristic of the pumping main/system.
When a fixed speed pump is pumping into a system, it will operate at the point at which its pump curve intersects the system curve.
A pump that is designed to run solo is selected to have its best efficiency point at the solo operating point.
Note: Not all pumps are designed to run solo. Pumps can also be designed to run in parallel and can be selected to have their best efficiency point at a parallel pumping operating point.