Centri fugal pumps design
fluid flow in a centrifugalpump
Design based on the following parameters
• Capacity range of liquid to be moved
• Differential head required
• Shape of head capacity curve
• Pump speed
• Liquid characteristics
Differential head required:
The head to be generated by the pump is determined from the system losses for various flow rates. For any
desired flow rate, the head to be generated by the pump or pumps, can be read directly (Figures 1-1
Shape of head capacity curve:
unstable or hooked curves (Figure 1-4) where the maximum developed head is at some flow greater than zero
are undesirable in applications where multiple pumps operate in parallel. In such applications, zero flow head
may be less than system head, making it impossible to bring a second pump on line. It is also possible for pumps
to deliver unequal flow with the discharge pressure from one pump determining the flow rate from another.
It should be noted that this tendency of instability is normally confined to the lower range of specific
speeds. As specific speed increases, the H-Q curve becomes more stable.
Pump speed may be suggested by the user to match electric frequency or available driver speed. The pump
manufacturer, however, has the ultimate responsibility and must confirm that the desired speed is compatible
with NPSHA and satisfies optimum efficiency selection.
Having intimate knowledge of the liquid to be pumped, the user will often specify materials to the pump
manufacturer. When the pump manufacturer is required to specify materials, it is essential that the user supply
all relevant information. Since liquids range from clear to those that contain gases, vapors, and solid material,
essential information includes temperature, specific gravity, pH level, solid content, amount of entrained air
and/or dissolved gas, and whether the liquid is corrosive.
As liquid flows through a pump, the hydrodynamic losses are in