How to Select a Submersible Sewage Pump

1. Clarify Medium Characteristics: Determine Pump Structure and Material Based on Sewage Composition

• Solid particle content and size
  If sewage contains solids like sand, gravel, silt, or construction debris (e.g., construction site drainage, river dredging), choose an impeller with cutting/tearing capabilities (such as vortex impellers or single/double-blade cutting impellers) to prevent clogging. For particles larger than 50mm, ensure the flow passage diameter is at least 1.5 times the maximum particle size.
  Example: When pumping sewage with 20–30mm gravel, select a cutting-type pump with a flow passage diameter of ≥40mm.
• Fibers and viscous substances
  For wastewater with high levels of long fibers (e.g., hair, cloth strips, pulp in domestic sewage or dyeing wastewater), use anti-clogging impellers (e.g., open impellers, spiral impellers). Optimize the gap between the impeller and pump casing (typically ≤3mm) to reduce blockages from fiber entanglement.
• Corrosiveness and temperature
  For sewage containing acids/alkalis (e.g., chemical or electroplating wastewater) or high temperatures (over 60°C), upgrade materials accordingly:
  • Mild corrosion (pH 6–8): Cast iron pump body + stainless steel impeller.
  • Moderate corrosion (pH 4–10): All stainless steel (304 grade).
  • Severe corrosion (pH <4 or >10): Special alloys (e.g., 316L) or rubber/lined plastic.
  • High-temperature sewage (60–100°C): Use a high-temperature motor (insulation class ≥F) and replace standard rubber seals with fluororubber.
• Density and viscosity
  If sewage density exceeds 1.2g/cm³ (e.g., sludge-rich slurry) or viscosity exceeds 50cP (e.g., food processing wastewater), adjust head and power based on “actual medium density/water density” (typically increasing power by 10%–20%).

2. Calculate Core Parameters: Flow Rate (Q) and Head (H) Precisely

1. Flow rate (Q): Determine using “maximum drainage volume + margin”

• Continuous drainage (e.g., sewage treatment plants): Calculate as “average hourly drainage × 1.2” (the 1.2 margin accounts for sudden volume spikes).
• Intermittent drainage (e.g., basement sump wells): Use “effective sump volume ÷ maximum allowed drainage time.” Example: A 50m³ sump requiring emptying in 30 minutes needs a flow rate of ≥100m³/h.
• Special cases: For systems handling both “daily drainage” and “storm emergencies,” calculate flow for both scenarios and select the higher value (or use a variable-frequency pump).

2. Head (H): Account for “total losses,” not just lifting height

• Lifting height: Vertical distance from the pump’s suction inlet to the discharge outlet (m).
• Pipeline friction loss: Friction along the pipeline (varies by material, diameter, and length). Example: A DN100 steel pipe loses ~5–8m of head per 100m.
• Local resistance loss: Resistance from elbows, valves, or tees (typically 20%–30% of friction loss).
• Safety margin: Add 10%–15% to account for pipeline aging or debris buildup.

3. Adapt to the Installation Environment: Scenario Dictates Installation and Protection

• Installation space
  • Small sumps (diameter <1.5m): Choose vertical submersible pumps (compact footprint).
  • Large tanks or open areas: Horizontal submersible pumps (easier to maintain).
  • Deep tanks (>5m): Check the pump’s maximum submersion depth (typically ≤10m) and ensure the cable length matches water depth + 1–2m.
• Protection and explosion resistance
  • Humid environments: Motor protection rating ≥IP68 (waterproof).
  • Explosive environments (e.g., methane-rich sewage wells): Use explosion-proof submersible pumps (rating ≥Ex d II BT4).
  • Outdoor installation: Add a rain cover to prevent motor overheating from direct sunlight.
• Mounting method
  • Temporary drainage or small pumps (<7.5kW): Free-standing (ensure a stable base to avoid shaking).
  • Long-term use: Equip with an automatic coupling system (connects the pump to rails for easy lifting during maintenance, no need to enter the tank).

4. Match Power and Additional Features: Avoid Waste or Underperformance

1. Power selection: Align with flow and head

• Avoid “underpowered pumps for heavy loads”: May cause motor burnout.
• Avoid “overpowered pumps for light loads”: Reduces efficiency (increases energy use by 30%+) and risks impeller cavitation.

2. Additional features: Choose only what you need

• Agitation function: For sewage with heavy sludge (e.g., septic tanks), select pumps with bottom agitating impellers to prevent sludge buildup.
• Automatic control: For unmanned areas (e.g., basements, remote pump stations), add level sensors (float or ultrasonic) to start/stop the pump at high/low levels and prevent dry running.
• Overload protection: Pumps with thermal relays or motor protectors automatically shut down during overloads or jams.
• Dual-pump systems: For high-flow scenarios (e.g., municipal pipelines), use “one active, one standby” setups to ensure continuous drainage during failures.

5. Key Mistakes to Avoid

1. Mismatched pipe and pump sizes: The pump’s outlet diameter should ≤ pipe diameter (e.g., 4-inch pump → 5-inch pipe) to prevent excessive resistance.
2. Ignoring temperature limits: Standard pumps handle ≤40°C; high-temperature models handle ≤80°C. Exceeding limits ages motor insulation.
3. Choosing unqualified brands: Prioritize certified brands (with ISO or sewage pump-specific certifications) to avoid issues like impeller breakage or seal leaks.

Summary: Submersible Sewage Pump Selection Steps

1. Analyze sewage composition (particles, fibers, corrosiveness, temperature) → Choose material and impeller type.
2. Calculate flow (with margin) and total head (with losses) → Match core parameters.
3. Determine installation method and protection level based on space and environment.
4. Select power and features (agitation, automation) → Optimize cost-effectiveness.