Sewage Screw Pump: What Operating Factors to Consider for Selection? Can Clogging Be Effectively Avoided?

1. Sewage Screw Pump Selection: What Core Operating Conditions Must Be Evaluated First?

When selecting a sewage screw pump, ignoring key operating conditions often leads to low efficiency, frequent failures, or even equipment damage. So, what core operating conditions must be evaluated first to ensure the pump matches the actual working scenario?

First, sewage viscosity and solid content are non-negotiable factors. For domestic sewage with low viscosity (similar to water) and solid content <5%, a standard single-screw pump with a flow passage diameter of 50-80mm is sufficient; for industrial sewage with high viscosity (e.g., containing sludge, grease) and solid content 5%-15%, a double-screw pump with a larger flow passage (≥100mm) and wear-resistant rotor material (such as nitrided steel) should be preferred. Taking a municipal sewage treatment plant as an example, its inlet sewage has a solid content of about 8% and contains small gravel. After selecting a double-screw pump with a 120mm flow passage, the pump's operating efficiency remained above 90% for 6 months, with no obvious wear.

Second, medium temperature and corrosiveness directly affect material selection. If the sewage temperature is 0-60℃ and non-corrosive (pH 6-8), cast iron pump bodies can be used to control costs; if the temperature exceeds 60℃ (e.g., industrial wastewater from chemical plants) or is corrosive (pH <4 or >10), stainless steel (304 or 316L) pump bodies and fluorine-lined rotors are necessary to prevent corrosion and deformation. A chemical factory once used a cast iron screw pump for acidic sewage (pH 2-3) with a temperature of 70℃; the pump body was corroded and leaked after only 1 month of use, and the replacement of a 316L stainless steel pump solved the problem.

Finally, lift and flow requirements determine the pump's model specifications. It is necessary to calculate the actual required lift (including pipeline resistance loss) and flow based on the sewage transportation distance and treatment capacity. For example, if the sewage needs to be transported 50 meters horizontally and 10 meters vertically, the calculated total lift is about 15 meters (adding 20% pipeline resistance), and the required flow is 50m³/h. At this time, a screw pump with a rated lift of 20 meters and a rated flow of 60m³/h should be selected to avoid overload caused by insufficient lift.

2. Sewage Screw Pump Clogging: What Are the Main Causes and Can They Be Effectively Avoided?

Clogging is one of the most common problems in sewage screw pump operation, which not only reduces efficiency but also increases maintenance costs. What are the main causes of clogging, and can they be effectively avoided through targeted measures?

The main causes of clogging include: ① large solid particles (e.g., plastic bags, branches) exceeding the flow passage diameter; ② long-fiber substances (e.g., hair, fabric scraps) winding around the rotor; ③ high-viscosity sludge accumulating in the flow passage and hardening.

In view of these causes, three-level prevention measures can be taken to effectively avoid clogging. The first level is pre-filtering: install a grid filter (aperture 10-20mm) at the pump inlet to intercept large particles and long fibers. For example, a food processing factory installed a 15mm aperture grid at the inlet of its sewage screw pump; the filter is cleaned once a day, and the pump has not been clogged for 1 year. The second level is structural optimization: choose screw pumps with anti-winding rotors (e.g., with spiral grooves on the rotor surface to cut long fibers) and self-cleaning flow passages (e.g., inclined flow passages to prevent sludge accumulation). A slaughterhouse replaced its ordinary screw pump with an anti-winding double-screw pump; the rotor's spiral grooves can cut hair and animal fibers into small segments, and the clogging frequency was reduced from once a week to once every 3 months. The third level is regular maintenance: formulate a maintenance plan according to the sewage quality—for high-viscosity sewage, clean the flow passage and rotor with high-pressure water (0.8-1.2MPa) every 2 weeks; for sewage with high fiber content, check the rotor winding situation every week and remove attachments in time.

A sewage treatment equipment manufacturer conducted a comparative test: two identical screw pumps were used to transport the same sewage (containing 10% solid content and long fibers). One pump adopted the three-level prevention measures, and the other did not. The results showed that the non-prevention pump was clogged 8 times in 1 month, with an average maintenance time of 2 hours each time; the pump with prevention measures was only clogged once, and the maintenance time was reduced to 30 minutes. This proves that clogging can be effectively controlled through scientific measures.

3. Sewage Screw Pump Selection: How to Match the Pump Type with Specific Application Scenarios?

Different application scenarios (e.g., municipal sewage, industrial wastewater, rural septic tanks) have very different sewage characteristics. How to accurately match the screw pump type with specific application scenarios to ensure stable operation?

For municipal sewage treatment plants (large flow, continuous operation, medium solid content), large-flow multi-screw pumps (flow range 100-500m³/h) with frequency conversion speed regulation functions are suitable. The frequency conversion function can adjust the speed according to the inlet sewage volume, avoiding energy waste, and the multi-screw structure has strong anti-clogging performance, which is suitable for 24-hour continuous operation. For example, a municipal sewage plant in a first-tier city uses 4 multi-screw pumps with a flow rate of 300m³/h and frequency conversion control; the average daily sewage treatment capacity reaches 7,000m³, and the energy consumption is 15% lower than that of ordinary pumps.

For small industrial workshops (small flow, intermittent operation, high corrosiveness), small single-screw pumps with compact structure and corrosion-resistant materials (e.g., 316L stainless steel) are more appropriate. These pumps have a small footprint (usually <0.5㎡), are easy to install, and can be started and stopped intermittently according to production needs. A small electroplating workshop produces 10m³ of acidic sewage per day; after selecting a single-screw pump with a flow rate of 15m³/h and a 316L pump body, it can complete the daily sewage transportation in 1 hour, with stable operation and no corrosion problems.

For rural septic tanks (small flow, low temperature, easy solid sedimentation), self-priming screw pumps with a built-in agitator are the best choice. The self-priming function avoids the need for manual priming, and the agitator can stir the precipitated sludge to prevent it from accumulating at the pump inlet. A village in the suburbs promoted self-priming screw pumps for 50 households' septic tanks; the pumps have a self-priming height of 5 meters and an agitator speed of 300r/min, which can effectively transport sludge with a solid content of 10%, and the maintenance frequency is only once every 6 months.

4. Sewage Screw Pump Operation: What Daily Monitoring Measures Can Prevent Unexpected Failures?

Even if the pump is correctly selected, improper daily monitoring may lead to sudden failures (e.g., motor burnout, rotor jamming). What daily monitoring measures can be taken to prevent unexpected failures and extend the pump's service life?

First, real-time monitoring of key parameters is essential. Install sensors to monitor the pump's inlet and outlet pressure, motor current, and medium temperature. If the inlet pressure drops suddenly (indicating possible blockage at the inlet), the outlet pressure rises abnormally (indicating blockage in the pipeline), or the motor current exceeds the rated value (indicating overload), the control system should issue an alarm in time and automatically stop the pump if necessary. A paper mill installed a parameter monitoring system for its sewage screw pumps; when the inlet was blocked by paper scraps once, the system alarmed within 30 seconds and stopped the pump, avoiding motor burnout.

Second, regular inspection of vulnerable parts cannot be ignored. The vulnerable parts of screw pumps include rotor seals, bearings, and stator rubber. For rotor seals, check for leaks every week; if there is sewage seepage, replace the seal ring in time (preferably using fluorine rubber seals with good wear resistance). For bearings, check the temperature and vibration every month; if the bearing temperature exceeds 70℃ or there is abnormal noise, it indicates wear and needs to be replaced. For stator rubber, check for cracks or deformation every 3 months; if the rubber is hardened (due to high temperature or corrosion), replace the stator to prevent reduced sealing performance.

Finally, record and analyze operation data to predict maintenance needs. Establish an operation log to record the pump's daily operating time, flow, pressure, and abnormal conditions. By analyzing the data, we can predict the service life of vulnerable parts. For example, if the motor current gradually increases by 10% within 1 month, it may indicate that the rotor is worn and needs to be overhauled in advance. A sewage treatment enterprise used this method to predict the replacement of a stator 2 weeks in advance, avoiding unexpected downtime and reducing economic losses by about 5,000 yuan.