Pump Selection Helper

Pump Selection Helper

A practical decision-tree tool for selecting the appropriate pump type based on operating conditions, flow requirements, head, and fluid properties.

Pump Type Overview

Centrifugal Pumps (Dynamic)

Radial Flow (Centrifugal)

• Flow range: 10 - 100,000 gpm (0.6 - 6,300 L/s)
• Head range: 50 - 5,000 ft (15 - 1,500 m)
• Specific speed (Ns): 500 - 4,000 (US units)
• Applications: General purpose, high head, moderate to high flow
• Advantages: Simple, reliable, low maintenance, handles solids
• Limitations: Poor efficiency at low flow, not suitable for high viscosity

Mixed Flow

• Flow range: 500 - 20,000 gpm (30 - 1,260 L/s)
• Head range: 20 - 200 ft (6 - 60 m)
• Specific speed (Ns): 4,000 - 9,000 (US units)
• Applications: Irrigation, flood control, water supply
• Advantages: Good efficiency, handles moderate flow and head
• Limitations: Limited head capability

Axial Flow (Propeller)

• Flow range: 2,000 - 100,000 gpm (125 - 6,300 L/s)
• Head range: 5 - 50 ft (1.5 - 15 m)
• Specific speed (Ns): 9,000 - 15,000 (US units)
• Applications: Circulation, cooling water, drainage
• Advantages: Very high flow, compact
• Limitations: Low head only, sensitive to flow variations

Positive Displacement Pumps

Gear Pumps

• Flow range: 1 - 1,500 gpm (0.06 - 95 L/s)
• Pressure range: Up to 3,000 psi (200 bar)
• Viscosity range: 1 - 1,000,000 cP
• Applications: Lubrication oils, fuel transfer, hydraulics
• Advantages: Self-priming, handles viscous fluids, constant flow
• Limitations: Cannot handle abrasives, pulsating flow

Piston/Plunger Pumps

• Flow range: 0.1 - 5,000 gpm (0.006 - 315 L/s)
• Pressure range: Up to 50,000 psi (3,400 bar)
• Viscosity range: 1 - 100,000 cP
• Applications: High-pressure cleaning, oil/gas, chemical injection
• Advantages: Very high pressure, accurate metering
• Limitations: Pulsating flow, high maintenance, expensive

Diaphragm Pumps

• Flow range: 0.1 - 800 gpm (0.006 - 50 L/s)
• Pressure range: Up to 1,000 psi (70 bar)
• Applications: Corrosive chemicals, slurries, hazardous fluids
• Advantages: Seal-less, handles abrasives and solids
• Limitations: Limited pressure, pulsating flow

Screw Pumps (Progressive Cavity)

• Flow range: 1 - 2,000 gpm (0.06 - 125 L/s)
• Pressure range: Up to 1,500 psi (100 bar)
• Viscosity range: 1 - 1,000,000 cP
• Applications: Viscous fluids, slurries, shear-sensitive fluids
• Advantages: Non-pulsating, handles high viscosity, gentle pumping
• Limitations: Wear on rotor/stator, limited to moderate pressure

Specialty Pumps

Turbine Pumps (Vertical)

• Flow range: 50 - 10,000 gpm (3 - 630 L/s)
• Head range: 50 - 1,000 ft (15 - 300 m)
• Applications: Deep wells, booster stations, cooling towers
• Advantages: Space-efficient, handles high head
• Limitations: Complex installation, difficult maintenance

Jet Pumps

• Flow range: 5 - 100 gpm (0.3 - 6.3 L/s)
• Head range: 50 - 300 ft (15 - 90 m)
• Applications: Shallow/deep wells, remote locations
• Advantages: No moving parts in fluid, simple
• Limitations: Low efficiency (25-35%)

Airlift Pumps

• Flow range: 10 - 5,000 gpm (0.6 - 315 L/s)
• Applications: Wells, wastewater, sand/gravel
• Advantages: Simple, handles solids and corrosives
• Limitations: Very low efficiency, requires air compressor

Selection Criteria

1. Flow Rate Requirements

• Low flow (< 10 gpm / 0.6 L/s): Positive displacement preferred
• Medium flow (10 - 1,000 gpm / 0.6 - 63 L/s): Centrifugal or PD
• High flow (> 1,000 gpm / 63 L/s): Centrifugal (mixed or axial flow)

2. Head Requirements

• Low head (< 50 ft / 15 m): Axial flow centrifugal or PD
• Medium head (50 - 500 ft / 15 - 150 m): Radial centrifugal or PD
• High head (> 500 ft / 150 m): High-speed centrifugal or piston pumps

3. Specific Speed (Ns)

Specific speed determines the pump impeller type:

US Units: Ns = N × √Q / H^0.75 SI Units: Ns = N × √Q / H^0.75

Where:

• N = rotational speed (rpm)
• Q = flow rate (gpm or m³/h)
• H = head (ft or m)

Classification:

• Ns < 2,000: Radial flow (high head, low flow)
• Ns = 2,000 - 5,000: Francis vane (medium head/flow)
• Ns = 5,000 - 10,000: Mixed flow
• Ns > 10,000: Axial flow (low head, high flow)

4. Fluid Viscosity Effects

Low viscosity (< 100 cP):

• Centrifugal pumps work well
• No significant correction needed

Medium viscosity (100 - 1,000 cP):

• Centrifugal efficiency drops
• Consider positive displacement
• Apply viscosity corrections

High viscosity (> 1,000 cP):

• Positive displacement required
• Gear, screw, or piston pumps
• Centrifugal pumps ineffective

5. NPSH Requirements

Net Positive Suction Head prevents cavitation:

• NPSHa (Available) = Atmospheric pressure + Static head - Vapor pressure - Friction losses
• NPSHr (Required) = From pump curve (manufacturer data)
• Requirement: NPSHa > NPSHr + Safety margin (3-5 ft)

High NPSHr concerns:

• Use double suction impeller
• Lower pump speed
• Use inducer or booster pump
• Positive displacement (self-priming)

6. Efficiency Considerations

Best Efficiency Point (BEP):

• Centrifugal: Operate within 70-120% of BEP flow
• Peak efficiency: 60-85% for centrifugal
• PD pumps: 70-90% (less flow-dependent)

Energy cost calculation: Annual cost = (BHP × 0.746 × Operating hours × kWh rate) / Efficiency

7. Cost Factors

Initial Cost:

• Centrifugal: $$ (lowest)
• Gear/Screw: $$$ (moderate)
• Piston/Plunger: $$$$ (highest)

Operating Cost:

• Energy consumption
• Maintenance frequency
• Spare parts availability

Life Cycle Cost = Initial + Installation + Energy + Maintenance + Downtime

Decision Tree for Pump Selection

START
  |
  ├─ Is fluid viscosity > 1,000 cP?
  |    YES → POSITIVE DISPLACEMENT
  |           ├─ High pressure (> 1,000 psi)? → PISTON/PLUNGER
  |           ├─ Shear-sensitive? → SCREW PUMP
  |           ├─ Abrasive/corrosive? → DIAPHRAGM
  |           └─ General viscous? → GEAR PUMP
  |
  NO ↓
  |
  ├─ Is constant flow required despite pressure changes?
  |    YES → POSITIVE DISPLACEMENT (Gear, Piston, or Screw)
  |
  NO ↓
  |
  ├─ Calculate Specific Speed: Ns = N × √Q / H^0.75
  |
  ├─ Ns < 500? (Very high head, low flow)
  |    YES → TURBINE or HIGH-SPEED CENTRIFUGAL
  |
  ├─ Ns = 500 - 4,000? (High head, moderate flow)
  |    YES → RADIAL CENTRIFUGAL
  |           ├─ Deep well? → VERTICAL TURBINE
  |           └─ Surface? → HORIZONTAL CENTRIFUGAL
  |
  ├─ Ns = 4,000 - 9,000? (Moderate head, high flow)
  |    YES → MIXED FLOW CENTRIFUGAL
  |
  ├─ Ns > 9,000? (Low head, very high flow)
  |    YES → AXIAL FLOW (PROPELLER)
  |
  └─ Special Conditions?
       ├─ Self-priming required? → PD or JET PUMP
       ├─ No electricity available? → ENGINE-DRIVEN
       ├─ Solids > 10% by volume? → DIAPHRAGM or SCREW
       └─ Metering accuracy critical? → PISTON or DIAPHRAGM

Application-Specific Recommendations

Water Supply

• Municipal: Horizontal split-case centrifugal (high reliability)
• Wells: Vertical turbine or submersible
• Booster: Multistage centrifugal
• Typical: Q = 100-5,000 gpm, H = 50-500 ft

HVAC/Cooling

• Chilled water: End-suction or inline centrifugal
• Condenser water: Horizontal split-case
• Typical: Q = 50-2,000 gpm, H = 30-150 ft

Chemical Processing

• Corrosive: Lined centrifugal or diaphragm
• Viscous: Gear or screw pumps
• Metering: Diaphragm or piston
• Typical: Q = 1-500 gpm, P = 50-500 psi

Oil & Gas

• Transfer: Centrifugal or screw
• Injection: High-pressure piston
• Crude oil: Screw pumps (viscous)
• Typical: Q = 10-1,000 gpm, P = 100-5,000 psi

Wastewater

• Raw sewage: Submersible non-clog centrifugal
• Sludge: Progressive cavity (screw)
• Chemical feed: Diaphragm metering
• Typical: Q = 50-5,000 gpm, H = 20-200 ft

Agriculture/Irrigation

• Surface water: Horizontal centrifugal
• Wells: Vertical turbine
• Drip irrigation: Centrifugal with filtration
• Typical: Q = 100-5,000 gpm, H = 50-300 ft

Mining/Slurry

• Heavy slurry: Horizontal slurry pump (rubber-lined)
• Abrasive: Hard-metal or ceramic-lined
• Dewatering: Submersible or horizontal centrifugal
• Typical: Q = 100-10,000 gpm, H = 50-500 ft

Food & Beverage

• Sanitary: Centrifugal (polished, 3A certified)
• Viscous products: Lobe or screw pumps
• CIP/Cleaning: Centrifugal
• Typical: Q = 10-500 gpm, P = 50-150 psi

Usage Guide

Using selector.py

Run the interactive selector:

python selector.py

Or use programmatically:

from selector import select_pump, calculate_specific_speed

# Example 1: Water supply
result = select_pump(
    flow_rate=500,      # gpm
    head=200,           # ft
    viscosity=1,        # cP
    fluid_type="water",
    speed=1750          # rpm
)
print(result)

# Example 2: High viscosity
result = select_pump(
    flow_rate=50,
    head=100,
    viscosity=5000,
    fluid_type="oil",
    temp=100            # °F
)
print(result)

Quick Selection Guidelines

1. Start with flow and head - These are primary factors
2. Check fluid properties - Viscosity, corrosiveness, abrasiveness
3. Calculate specific speed - Determines centrifugal type
4. Verify NPSH - Ensure adequate suction conditions
5. Consider operating range - Pump should operate near BEP
6. Evaluate life cycle cost - Not just initial cost
7. Check maintenance access - Space for service
8. Review manufacturer curves - Verify actual performance

Common Mistakes to Avoid

• ❌ Oversizing pumps (reduces efficiency, increases cost)
• ❌ Ignoring viscosity effects on centrifugal pumps
• ❌ Insufficient NPSH margin (causes cavitation)
• ❌ Operating far from BEP (premature wear)
• ❌ Selecting based on initial cost only
• ❌ Not considering future expansion needs
• ❌ Ignoring system curve changes

References

See reference.md for:

• Detailed pump selection charts
• Specific speed ranges from industry standards
• Manufacturer selection guides
• Performance curve examples
• NPSH calculation methods