| name | pump-selection-helper |
| description | Decision tree for selecting pump type based on flow, head, and fluid properties |
| category | helpers |
| domain | mechanical |
| complexity | basic |
| dependencies | [] |
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
result = select_pump(
flow_rate=500,
head=200,
viscosity=1,
fluid_type="water",
speed=1750
)
print(result)
result = select_pump(
flow_rate=50,
head=100,
viscosity=5000,
fluid_type="oil",
temp=100
)
print(result)
Quick Selection Guidelines
- Start with flow and head - These are primary factors
- Check fluid properties - Viscosity, corrosiveness, abrasiveness
- Calculate specific speed - Determines centrifugal type
- Verify NPSH - Ensure adequate suction conditions
- Consider operating range - Pump should operate near BEP
- Evaluate life cycle cost - Not just initial cost
- Check maintenance access - Space for service
- 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
