In slurry transportation systems, pump head is one of the key parameters used to determine the appropriate slurry pump.

Many people simply understand pump head as “how high a pump can lift slurry,” but the actual situation is more complex. Pump head represents the energy gained by a unit weight of liquid as it passes through the pump. In an actual conveying system, the head that the pump needs to provide is related to the liquid levels, pipeline losses, pressure conditions, and operating conditions of the system.

It is also important to note that slurry pump manufacturers generally provide performance curves based on clear water performance. However, the actual fluid being transported is usually slurry containing solid particles. Therefore, a clear-water performance curve cannot be directly considered the final pump performance under actual slurry operating conditions.

This article explains the basic concept of slurry pump head, pump head calculation, how to read clear-water performance curves, and the main factors that need to be considered when selecting a slurry pump for actual slurry service.

1. What Is Slurry Pump Head?

Pump head is the energy gained by a unit weight of liquid as it passes through the pump, and it is normally expressed in meters of liquid column (m).

Based on the total head at the pump inlet and outlet, pump head can be expressed as:

H = H₂ − H₁

Where:

• H — Pump head (m)

• H₂ — Total head at the pump outlet (m)

• H₁ — Total head at the pump inlet (m)

Therefore, pump head is not simply equal to the vertical lifting height.

In an actual slurry transportation system, the energy that the pump needs to provide is also related to the friction head losses, local head losses, and outlet velocity head loss in the inlet and outlet pipelines.

2. How Are the Inlet and Outlet Total Heads Determined?

According to slurry pump technical data, the inlet total head can be determined from the inlet pipeline conditions, including the following factors:

• Friction head loss in the inlet pipeline (m)

• Total local head loss in the inlet pipeline (m)

• Inlet liquid level height

For a horizontal pump, the inlet liquid level height is measured from the pump shaft centerline to the suction liquid level. If the liquid level is below the pump shaft centerline, the value is negative.

For a vertical pump, the reference point is the outer end of the impeller blade inlet edge. If the liquid level is below the impeller inlet edge, the value is negative.

Similarly, the outlet total head is determined by:

• Friction head loss in the outlet pipeline (m)

• Total local head loss in the outlet pipeline (m)

• Outlet velocity head loss

• Outlet liquid level height

For a horizontal pump, the outlet liquid level height is measured from the pump shaft centerline to the discharge liquid level.

For a vertical pump, it is measured from the outer end of the impeller blade inlet edge to the discharge liquid level.

From an engineering perspective, this means that pump head calculation cannot be based only on the elevation difference. The complete hydraulic conditions at the pump inlet and outlet must be considered.

3. What Is the Difference Between Pump Head and Pressure?

Head and pressure are not the same parameter.

Pump head is normally expressed in meters of liquid column, while pressure is commonly expressed in Pa, kPa, bar, or other pressure units.

The relationship between pressure difference and pump head can be expressed as:

ΔP = ρgH

Where:

• ΔP — Pressure difference

• ρ — Density of the transported medium

• g — Gravitational acceleration

• H — Pump head

Therefore, at the same pump head, fluids with different densities will produce different pressure differences.

This is particularly important for slurry pumps because slurry density is generally higher than that of clear water.

However, it is important to understand that:

An increase in slurry specific gravity does not mean that pump head will increase proportionally.

Slurry specific gravity mainly affects pressure and power requirements, while actual slurry performance is also affected by solids concentration, particle size, viscosity, and particle characteristics.

4. What Is Total Dynamic Head (TDH)?

Pump head is the head actually provided by the pump under a specific operating condition, while Total Dynamic Head (TDH) is the total head required by the conveying system at a specific flow rate.

Simply put:

• TDH indicates how much head the system requires.

• Pump head indicates how much head the pump can provide.

During slurry pump selection, the pump must be capable of meeting the required TDH at the target flow rate.

5. What Is the Difference Between Clear-Water Performance and Actual Slurry Performance?

Clear-water performance curves and actual slurry performance can differ.

Clear water is commonly used for pump performance testing and performance verification. Therefore, CNSME® performance curves are generally based on clear-water performance.

When expressed as liquid head, pump head mainly represents the unit-weight energy provided by the pump. Under the same pump type, speed, and flow conditions, a change in fluid density does not cause pump head to change proportionally.

However, when the transported medium changes from clear water to slurry containing solid particles, factors such as slurry concentration, particle size, viscosity, particle shape, and settling characteristics can affect the actual operating performance of the pump.

In general, when pumping high-concentration or coarse-particle slurry, the actual pump head and efficiency may be lower than the clear-water performance. The abrasiveness of the slurry, meanwhile, mainly affects the wear and service life of wet-end components.

Therefore, the clear-water performance curve is an important basis for slurry pump selection, but it should not be directly regarded as the final pump performance under actual slurry operating conditions.

For example, the CNSME 4/3 AH slurry pump performance curve is marked:

PERFORMANCE FOR CLEAR WATER

This means that the curve represents the basic performance of the pump under clear-water conditions, including:

• Flow Rate

• Head

• Speed (RPM)

• Efficiency

• NPSHr

However, the actual operating medium is usually mineral slurry, tailings, or other slurry containing solid particles.

The following slurry characteristics can affect actual pump performance:

• Slurry Specific Gravity (Sm)

• Solids Concentration

• Solid Particle Size

• Viscosity

• Particle Shape and Characteristics

• Settling Characteristics

Compared with clear water, pumping high-concentration, coarse-particle slurry may result in a significant reduction in actual pump head and efficiency.

For some fine-particle slurries, pump efficiency may increase under specific conditions.

Therefore:

The clear-water performance curve is an important basis for slurry pump selection, but it cannot be directly regarded as the final performance under actual slurry operating conditions.

Actual pump selection should evaluate slurry performance according to the specific slurry properties and operating conditions.

6. How to Read a 4/3 AH Slurry Pump Performance Curve

The CNSME 4/3 AH slurry pump performance curve is used here as an example.

The curve helps users understand the basic performance relationships of a slurry pump.

Flow Rate

The horizontal axis represents flow rate, normally expressed in m³/h.

It indicates the conveying capacity of the pump under the corresponding operating conditions.

Head

The vertical axis represents pump head, expressed in m.

At the same speed, flow rate and pump head normally have a corresponding relationship. As the operating flow changes, the head that the pump can provide also changes.

Therefore, you should not look only at the maximum head of a pump. Instead, you should determine how much head the pump can provide at the required flow rate.

RPM

The performance curve contains pump performance data at different rotational speeds.

After determining the target flow rate and required head, the appropriate operating speed can be identified from the performance curve to match the required duty point.

Efficiency

The efficiency areas on the curve indicate pump efficiency under different operating conditions.

During actual selection, the pump should operate within a reasonable operating range. Efficiency, wear, NPSH, and potential system changes should all be considered rather than simply pursuing the highest efficiency point.

NPSHr

The 4/3 AH performance curve contains markings such as:

3 m, 4 m, 6 m, 8 m, 10 m

These values correspond to NPSHr (Net Positive Suction Head Required) data.

During actual pump selection, the pump's NPSHr should be compared with the NPSHa available from the system, with an appropriate engineering margin provided to reduce the risk of cavitation.

NPSHa represents the effective net positive suction head available from the system, while NPSHr represents the net positive suction head required by the pump under a specific operating condition.

Clear Water Performance

One final point is particularly important:

The 4/3 AH performance curve is a clear-water performance curve.

If the actual application involves high-concentration mineral slurry, coarse-particle slurry, or other special slurry conditions, the clear-water performance shown on the curve should not be directly treated as the actual operating performance.

7. What Is the Pump Duty Point?

The pump duty point is normally determined by:

Flow Rate + Head

For example, a slurry transportation system may require:

• A specified target flow rate

• A corresponding system head at that flow rate

This combination of flow rate and head represents an important duty point for pump selection.

In an actual system, pump performance must match the system requirements.

Therefore:

The maximum head of a pump is not the same as its actual operating head.

A pump may be capable of achieving a relatively high maximum head, but it may not be able to provide the same head at the target flow rate.

This is why slurry pump selection must consider both Flow Rate and Head.

8. How to Select a Slurry Pump Based on Flow Rate and Head

Slurry pump selection can generally follow the steps below.

① Determine the Required Flow Rate

First, determine the required conveying capacity of the system:

Q = Required Flow Rate

② Calculate the Required System Head

Calculate the required system head according to the inlet conditions, outlet conditions, and pipeline system.

Key factors include:

• Liquid level height

• Pipeline length

• Pipe diameter

• Friction losses

• Local losses

• Pressure conditions

③ Determine the Duty Point

Define:

Flow Rate + Required Head

as the primary duty point for pump selection.

④ Perform Preliminary Matching Using the Performance Curve

Use the manufacturer's performance curve to determine the pump type and operating speed capable of covering the target duty point.

⑤ Evaluate Actual Slurry Performance

The clear-water performance curve can only be used as a preliminary basis for selection.

Actual selection should also consider operating parameters such as:

• Slurry specific gravity (Sm)

• Solids concentration

• Maximum particle size

• Viscosity

• Particle characteristics

• Settling characteristics

These parameters are used to evaluate pump performance under actual slurry conditions.

⑥ Confirm the Mechanical Configuration

After determining the flow rate, head, and slurry conditions, the pump's mechanical configuration must also be confirmed, including:

• Impeller

• Wet-end components

• Pump frame/bracket

• Bearing assembly

• Shaft

• Drive arrangement

• Motor power

For horizontal slurry pumps, the pump bracket and bearing assembly must be matched to the mechanical load capacity, shaft diameter, drive configuration, and operating conditions.

Therefore, the pump bracket is also part of the final pump selection, rather than something that can be determined solely from the pump inlet and outlet sizes.

9. Why Can't Slurry Pump Selection Be Based Only on Head?

“Choose a pump whose maximum head reaches the required number of meters” is a common approach, but this method cannot guarantee that the pump will meet the actual operating conditions.

Slurry pump performance is closely related to flow rate, head, speed, slurry properties, and the mechanical configuration of the pump.

For the same flow and head requirements, different slurry concentrations, particle sizes, and abrasive characteristics may require completely different pump types, operating speeds, impellers, and wet-end components.

Therefore, slurry pump selection should consider:

Flow Rate + Head + Slurry Properties + Pump Performance + Mechanical Configuration

rather than selecting a pump simply according to its maximum head.

10. What Data Should Be Provided for Slurry Pump Selection?

If you need a slurry pump manufacturer to perform pump selection, it is recommended that you provide the following basic operating data:

The more complete the operating data, the easier it is for the manufacturer to determine the appropriate pump type, operating speed, wet-end components, pump bracket, and motor configuration.