GH 150 High‑Head Gravel Pump Critical Velocity Calculation for Long‑Distance Sand Transport: Preventing Sedimentation Blockage

Subtitle: Flow below critical velocity causes sand settling and pipe blockage – critical velocity formula, parameter values, and minimum flow requirements for different pipe diameters

Introduction

The GH 150 is a high‑head gravel pump in the GH series (150mm discharge), with single‑stage head up to 60‑80 meters. It is widely used in river sand mining, long‑distance sand transport, and reclamation. When transporting sand‑water mixtures over long pipelines, if the velocity is too low, sand particles settle at the pipe bottom due to gravity, gradually forming a sand bed and eventually blocking the pipeline. Blockage not only interrupts transport but is difficult to clear and can damage the pump and pipeline.

Preventing sedimentation requires maintaining the transport velocity above the critical velocity – the minimum velocity at which sand particles remain suspended. Critical velocity depends on particle size, density, pipe diameter, and concentration. Hebei Xingou Machinery Equipment Co., Ltd., based on classical two‑phase flow theories (Durand, Wilson) and field data from GH 150 pumps, has developed a simplified critical velocity calculation method. This article provides the formula, parameter tables, and a quick reference of minimum safe flow rates for different pipe diameters to help users avoid sedimentation blockage.

1. Sedimentation Mechanism and Hazards

1.1 Sedimentation Process

In a horizontal pipe, sand particles are subject to forward drag force and downward gravity. At sufficiently high velocity, turbulence keeps particles suspended. When velocity falls below a critical value, gravity dominates, and coarse particles begin sliding, saltating, and eventually forming a stationary sand bed.

1.2 Hazards of Blockage

• Sudden pressure rise, pump overload trip

• Shutdown for pipe cutting and cleaning – hours to days

• Repeated deposition and restart accelerate pipe wall erosion

• Severe cases may rupture pump casing or pipeline

2. Critical Velocity Calculation Basis

The behavior of solid particles in pipes is complex. Empirical formulas are commonly used in engineering. This article uses simplified forms of the Durand formula (for coarse particles, high concentration) and Wilson formula (for fine particles, low concentration).

2.1 General Critical Velocity Formula

For sand‑water mixtures transported by GH 150 pumps (particle size 0.1-5 mm), the following simplified formula applies:

Vc = FL × √[2g × D × (ρs - ρw) / ρw]

Where:

• Vc = critical velocity (m/s)

• FL = empirical coefficient (depends on particle size and concentration, typically 0.8-1.2)

• g = gravity acceleration (9.81 m/s²)

• D = pipe inner diameter (m)

• ρs = sand density (kg/m³, quartz ~2650)

• ρw = water density (1000 kg/m³)

For typical sand mining, a simplified form is:

Vc = Coefficient × √D

The coefficient ranges from 5.0 to 7.0 (D in m, Vc in m/s). More precise values are given in the table below.

3. Parameter Values and Corrections

3.1 Empirical Coefficient FL

3.2 Safety Margin

To avoid fluctuations near the critical point, design velocity should be 15%-20% above Vc:

V_design = (1.15 ~ 1.20) × Vc

4. Quick Reference: Critical Velocity and Minimum Flow for Common Pipe Sizes

Example: Quartz sand (ρs=2650 kg/m³), medium particle size (d50=1 mm), volumetric concentration Cv=15%.

Note: GH 150 pump discharge is 150 mm, optimal flow range 200-400 m³/h. Using DN150 pipe, the minimum safe flow (190 m³/h) is below the pump's lower optimal flow, so normal operation avoids sedimentation. However, if DN200 pipe is used, a flow of 395 m³/h is needed – which may exceed pump capability.

5. Pipe Selection Recommendations for GH 150

Key principle: Pipe ID should not be two or more sizes larger than the pump discharge, otherwise sedimentation is very likely at low flow.

6. Field Calculation Example

Case: A sand mining site uses a GH 150 pump with a 150 mm ID pipe. Sand particle size d50 = 0.8 mm, volumetric concentration Cv = 12%. Calculate critical velocity and safe flow.

Steps:

1. From table, take FL = 0.95 (medium sand, moderate concentration).

2. Calculate critical velocity:
   Vc = 0.95 × √(2×9.81×0.15×(2650-1000)/1000) = 0.95 × √(2×9.81×0.15×1.65) ≈ 0.95 × √4.86 ≈ 0.95 × 2.20 = 2.09 m/s.

3. Design velocity: V_design = 2.09 × 1.15 = 2.40 m/s.

4. Minimum safe flow: Q = V × A = 2.40 × (π×0.15²/4) × 3600 ≈ 2.40 × 0.01767 × 3600 ≈ 153 m³/h.

5. Conclusion: Pump flow should be maintained above 150 m³/h. GH 150's normal operating range fully meets this.

7. Early Warning Signs and Operating Procedures

7.1 Early Signs of Sedimentation

7.2 Operating Procedures to Prevent Sedimentation

• Start with clean water, then gradually add sand.

• Before shutdown, flush the pipeline with clean water for 5-10 minutes to empty sand.

• Install pressure taps along long pipelines to monitor pressure gradient.

• For low‑flow periods, use intermittent transport or recirculation flushing.

Conclusion

For long‑distance sand transport with GH 150 high‑head gravel pumps, preventing pipeline sedimentation blockage requires keeping flow velocity above the critical velocity. The Durand‑type empirical formula Vc = FL × √[2gD(ρs-ρw)/ρw] provides a quick calculation. In design, add a 15%-20% safety margin above Vc, then select pipe diameter and operating flow accordingly. With GH 150 pump (150mm discharge) and DN150 pipe, normal operating flows of 200-400 m³/h are well above the critical flow, giving low sedimentation risk. Hebei Xingou Machinery Equipment Co., Ltd. offers pipeline system design consulting and GH series pump support. Contact us for critical velocity calculation spreadsheets.