How to read the performance curve of a slurry pump?

A pump performance curve is a graphical representation of a pump's operational characteristics under a constant speed. For slurry pumps, understanding this curve is critical for proper selection, ensuring efficient operation, and preventing premature wear or failure. It answers the fundamental question: "For a given flow rate, what head will the pump generate, how much power will it require, and at what efficiency will it operate?"

1. The Purpose of the Performance Curve

The curve describes the relationship between the pump's Flow Rate (Q) and its key performance parameters:

Head (H)

Efficiency (η)

Power Input (P)

Required Net Positive Suction Head (NPSHr)

These relationships are established using clear water as the pumped liquid and must be corrected for the actual slurry properties.

2. Understanding the Axes: Flow vs. Head

X-Axis: Flow Rate (Q)

Units: Typically cubic meters per hour (m³/h), liters per second (L/s), or US gallons per minute (US gpm).

Meaning: The volume of fluid delivered per unit of time.

Y-Axis (Left): Head (H)

Units: Meters (m) or feet (ft).

Meaning: The energy imparted to the liquid by the pump, expressed as the height of a column of that liquid. It is used to overcome system pressure, elevation gain, and friction losses.

The Core Relationship: The Q-H curve is the descending curve showing that as flow increases, the pump generates less head.

3. Key Curves and Information on the Chart

a) Efficiency Curve (η)

Shape: An inverted U-shaped curve.

Meaning: Represents the ratio of hydraulic power output to mechanical power input. Its peak is called the Best Efficiency Point (BEP).

Importance: Operating at or near the BEP ensures minimal energy consumption, reduced wear, and stable operation. Pump selection should always target a duty point as close to the BEP as possible.

b) Power Input Curve (P)

Shape: A curve that rises with increasing flow.

Meaning: The mechanical power required at the pump shaft.

Critical Warning for Slurry Pumps: The power curve is rising, meaning power is lowest at shut-off (zero flow). Therefore, slurry pumps must NEVER be started against a closed discharge valve, as it will cause motor overload. This is a crucial difference from many clean-water centrifugal pumps.

c) Required NPSH Curve (NPSHr)

Shape: A steeply rising curve, often plotted on a secondary Y-axis.

Meaning: The minimum absolute pressure required at the pump inlet to prevent cavitation. A lower NPSHr indicates better cavitation resistance.

Rule: The Net Positive Suction Head Available from the system (NPSHa) must be greater than the pump's NPSHr, typically by a safety margin of 0.5 - 1.5 meters. If NPSHa < NPSHr, cavitation occurs, damaging the pump and degrading performance.

d) Iso-Efficiency Curves

Shape: concentric, elliptical curves surrounding the BEP.

Meaning: They connect points of equal efficiency, allowing you to see the efficiency at operating points away from the main efficiency curve.

4. A Step-by-Step Guide to Reading the Curve

Let's assume a system requires a pump to deliver 100 m³/h at 50m of Total Dynamic Head (TDH).

Locate the Flow: Find 100 m³/h on the X-axis and draw a vertical line upward.

Find the Head: Where this vertical line intersects the Q-H curve, draw a horizontal line to the Y-axis. This gives the head produced at that flow (e.g., 52m).

Conclusion: The pump produces 52m of head, which is sufficient for the system requirement of 50m. The actual operating point will be where the pump curve and the system curve intersect.

Check the Efficiency: From the same intersection point, determine the efficiency. It may lie directly on the η curve or between iso-efficiency lines (e.g., 72%). Compare this to the BEP (e.g., 75%).

Conclusion: An efficiency of 72% is excellent and close to the BEP, indicating a well-sized pump.

Determine the Power Draw: From the intersection point, draw a horizontal line to the Power (P) axis (often on the right). Read the power value (e.g., 22 kW).

Motor Sizing: The motor must be sized to handle this power, plus a safety margin (often 10-20%). A 30 kW motor would be a appropriate selection.

Check for Cavitation: Find the NPSHr value at the same flow rate (e.g., 4.5m).

System Check: You must calculate the NPSHa for your system. It must be greater than 4.5m (e.g., >5.5m). If not, the pump installation must be modified.

5. The Critical Difference: Clean Water vs. Slurry Performance

This is the most important concept in slurry pump selection. The published curve is for water. Slurry properties (specific gravity, solids concentration, size, and type) drastically alter performance.

Head Ratio Factor (HRF): Slurry produces lower head than water.

Slurry Head, H_s = H_w × HRF (where HRF < 1)

Efficiency Ratio Factor (ERF): Pump efficiency is reduced when handling slurry.

Slurry Efficiency, η_s = η_w × ERF (where ERF < 1)

Slurry Power Calculation: The required power increases due to higher density and performance deration.

The accurate formula is: P_s = P_w × (ρ_s / ρ_w) × (HRF / ERF)

A common simplification is: P_s ≈ P_w × Specific Gravity of Slurry × HRF

These correction factors (HRF, ERF) are provided by the pump manufacturer based on slurry characteristics and test data.

Therefore, the correct slurry pump selection process is:

Select a pump based on the clear water performance curve.

Apply the slurry correction factors to find the pump's actual slurry performance (H_s, η_s, P_s).

Verify that these corrected values meet your system requirements.

Size the motor based on the corrected slurry power (P_s).

If you need know more detailed Curve about Warman AH pump , you can keep going on :

Warman AH SLURRY PUMP