Sewage Lift Station Pump: Dry-Pit and Submersible Design

Sewage lift stations pump wastewater from lower to higher elevation in municipal and industrial sewer systems. These stations handle raw sewage with solids, debris, and corrosive gases, requiring non-clog pumps and reliable controls. This guide covers lift station design, dry-pit vs submersible pumps, wet well design, and pump selection.

Sewage Lift Station Types

Critical: Submersible vs Dry-Pit

Critical: Non-Clog Pump Design

• Impeller types: (1) Vortex (recessed) impeller — impeller recessed in volute, large free passage (75–100mm), fluid moves by vortex, BEST for debris/rags, but lower efficiency (45–60%), (2) Single-channel impeller — one large channel, good solids handling, efficiency 60–75%, (3) Multi-channel (2/3 vane) — higher efficiency (70–85%), smaller passage, more clogging risk, (4) Chopper/cutter impeller — cuts solids, for heavy debris, but higher power, wear. Our submersible sewage pumps offer vortex and channel impellers.
• Free passage: Minimum 75–100mm for municipal sewage (passes 75mm sphere). Critical for non-clog. NEVER use standard clean-water impeller for sewage.
• Shaft seal: Submersible = double mechanical seal (silicon carbide/carbon) with oil chamber (lubrication + leak detection). Seal failure = water enters motor → burnout. Seal leak detection (electrode) standard. Our submersible pumps have double seals + leak detection.

Critical: Wet Well Design

Critical: Flow and Peak Factor

• Average dry weather flow (ADWF): Base sewage flow (per capita 150–250 L/day × population + industrial + infiltration).
• Peak factor: Peak flow / average flow. Typical: (1) small residential 3–5×, (2) medium municipal 2–3×, (3) large 1.5–2×. Pump station must handle peak flow without surcharge (sewer backup).
• Staging: Multiple pumps stage on as level rises: Pump 1 (duty) starts at level 1, Pump 2 at level 2 (peak), Pump 3 at level 3 (extreme/backup). Alternating duty equalizes wear.
• Infiltration/inflow (I/I): Rainwater enters sewer (cracks, connections) → flow increases dramatically during storms. Design for I/I (often 2–5× ADWF). Critical for combined sewers.

Critical: Head Calculation

• Static head: Elevation difference between wet well low level and discharge point (force main to gravity sewer or treatment plant).
• Friction head: Force main friction (Darcy-Weisbach or Hazen-Williams). Sewage force mains 100–500mm, velocity 0.6–2.5 m/s (minimum 0.6 m/s to prevent sediment, maximum 3 m/s to prevent wear). C-factor: ductile iron C=130, PVC C=150, concrete C=120.
• Minor losses: Entrance, exit, bends, valves, check valve. Check valve significant (0.5–2m). Use low-loss check valve (nozzle check) for large stations.
• TDH: Static + friction + minor. Sewage lift pumps typically 10–60m head.

Critical: Materials and Corrosion

Critical: Common Problems

• Problem 1: Pump clogs (rags, wipes, debris). Modern sewage has "flushable" wipes, rags, plastic → clog impeller. Solution: vortex impeller (large passage), chopper pump, inlet screen,定期 cleaning. Our vortex non-clog pumps minimize clogging.
• Problem 2: Seal failure (submersible motor burnout). Double mechanical seal fails → water enters motor → burnout. Solution: quality double seal (SiC/carbon), oil chamber, leak detection,定期 inspection, proper cable entry. Our submersible pumps have reliable seals.
• Problem 3: Wet well septicity / H2S. Long retention, warm temp → septic → H2S gas → odor, crown corrosion, safety hazard. Solution: minimize wet well volume (but not below cycling limit), forced main flushing, H2S monitoring, ventilation, chemical dosing (iron salts, nitrate). Our designs minimize septicity.
• Problem 4: Excessive cycling (wet well too small). Small wet well → pumps start/stop frequently → motor thermal stress, reduced life. Solution: wet well volume ≥5× flow/starts, proper level hysteresis. Our designs size wet wells correctly.
• Problem 5: Vortex / air entrainment. Low level → vortex → air + sewer gas ingestion → cavitation, vibration, gas in force main. Solution: minimum submergence, anti-vortex plates, baffles. Our wet well designs prevent vortices.
• Problem 6: Force main sedimentation (low velocity). Velocity ＜0.6 m/s → solids settle → pipe blockage, septicity. Solution: minimum velocity 0.6 m/s (1 m/s preferred),定期 flushing, proper pipe sizing. Our designs maintain scouring velocity.

Selection Summary

1. Small-medium station (most common): Submersible non-clog pump (vortex or single-channel impeller, 75–100mm passage, 10–2000 m³/h, 10–50m, double seal + leak detection, guide rail + hoist, 2–4 pumps N+1)
2. Large municipal / high head: Dry-pit horizontal or vertical pump (500–50,000 m³/h, high head, easy maintenance, ventilation, non-clog impeller)
3. Package station (small/commercial): Prefabricated submersible in fiberglass tank (5–500 m³/h, complete with controls)
4. Heavy debris / rags: Chopper pump or vortex impeller (cuts/passes large solids)
5. Industrial corrosive sewage: 316SS/d duplex or fluoroplastic pump (chemical resistance)
6. Critical: sewage lift = RAW SEWAGE (solids, rags, debris, H2S gas, corrosive) → non-clog impeller (vortex = best for debris, 75–100mm passage), submersible (most common, self-priming, compact) vs dry-pit (large, easy maintenance), wet well design (volume, anti-vortex, ventilation, H2S), peak flow (2–5× average, staging), force main velocity 0.6–2.5m/s (prevent sediment), double mechanical seal + leak detection, all = sewer reliability + flood prevention
7. Our submersible sewage pumps, split case dry-pit pumps, and fluoroplastic pumps cover sewage lift stations. For lift station design, talk to our wastewater engineers with your ADWF, peak factor, TDH, and station type.