Question 1

What is Total Dynamic Head (TDH)?

Accepted Answer

TDH is the total equivalent height the pump must lift the fluid, including: static head (actual elevation change), friction head (pipe losses), pressure head (tank pressure requirements), and velocity head (usually negligible). TDH determines the pump's operating point on its curve.

Question 2

How do I choose between different pump types?

Accepted Answer

Pump type depends on specific speed (Ns): Ns < 30 = radial/centrifugal (high head, low flow), Ns 30-80 = mixed flow (medium head/flow), Ns > 80 = axial flow (low head, high flow). Centrifugal pumps are most common for general industrial applications.

Question 3

What is NPSH and why does it matter?

Accepted Answer

Net Positive Suction Head (NPSH) is the absolute pressure at the pump inlet above vapor pressure. NPSHa (available) must exceed NPSHr (required by pump) to prevent cavitation. Cavitation causes noise, vibration, reduced performance, and impeller damage.

Question 4

How do I improve low NPSH conditions?

Accepted Answer

To increase NPSHa: 1) Raise the liquid source level, 2) Reduce suction pipe friction (larger diameter, shorter length), 3) Lower liquid temperature, 4) Increase suction tank pressure, 5) Use a pump with lower NPSHr, or 6) Install a booster pump or inducer.

Question 5

What pump efficiency should I expect?

Accepted Answer

Typical centrifugal pump efficiency ranges: Small pumps (<5 kW): 50-65%, Medium pumps (5-50 kW): 65-80%, Large pumps (>50 kW): 75-88%. Efficiency varies with operating point - best efficiency point (BEP) should match your design flow.

Question 6

How does pump curve relate to system curve?

Accepted Answer

The pump curve shows head vs. flow at constant speed. The system curve shows head required vs. flow (static + friction). The operating point is where they intersect. For variable flow, use VFD to shift pump curve rather than throttling, which wastes energy.