Frequent Overloading & Sludge Leakage of Screw Press? TNW Shares Operation Guidelines for Screw Dewatering Machines

Frequent Overloading & Sludge Leakage of screw press? TNW Shares Operation Guidelines for Screw Dewatering Machines

Wastewater plant operators often encounter a troublesome issue: brand-new screw presses run smoothly at first, yet several months later, faults such as blocked stack plates, rising torque, drier sludge cake degradation and turbid filtrate with sludge leakage emerge one after another. Many operators assume the equipment has quality defects. In fact, most malfunctions stem from improper daily operation and maintenance accumulated over time.

As core sludge dewatering equipment, screw presses boast prominent advantages over plate-and-frame and belt filter presses: 24-hour continuous operation, small footprint and low energy consumption. Nevertheless, moving/fixed rings and spiral shafts are precision components requiring standardized operation and regular maintenance. As a screw press manufacturer providing maintenance services for all brands, TNW Environmental has dealt with numerous on-site failure cases. Based on years of field service experience, we sort out practical operation precautions to help operators reduce breakdowns and extend equipment service life.

1. Critical Operations During Startup

Inspect equipment status before startup

Check for hardened sludge or debris jamming between moving and fixed rings. Verify spray nozzle patency and reducer oil level. Do not start the machine until all components are confirmed normal. Direct no-load startup without clearing internal blockages easily causes excessive stress on the spiral shaft and triggers overload alarms.

Follow standard startup & shutdown sequence

Startup sequence: Turn on spray system → Start screw press main unit → Activate dosing system → Switch on sludge feed pump.

Feeding sludge prior to activating sprays and the main unit will harden sludge rapidly inside ring gaps and cause blockage within a short time.

Shutdown sequence: Stop sludge feed pump first, keep spraying to fully discharge internal sludge, then shut down the main unit. Emergency power-off shutdown is prohibited.

Reduce feed volume for initial commissioning or restart after long shutdown

Do not run at full load immediately after prolonged downtime. Conduct low-load trial operation for 30 minutes, gradually increase sludge flow, monitor filtrate status and torque, and adjust PAM dosage according to flocculation performance.

2. Key Control Points During Operation to Prevent Persistent Faults

Prioritize flocculation effect; proper chemical dosing is essential

Approximately 70% of dewatering performance depends on flocculation. Fine flocs and poor solid-liquid separation should not be addressed simply by increasing chemical dosage. Excessive PAM consumption raises operating costs and causes sludge accumulation within ring gaps. Adjust chemical type and dosage via lab tests timely when sludge characteristics fluctuate due to rainy seasons or process modifications.

Prevent hard grit from entering the machine

Sand-laden sludge from sand washing projects, river dredging and certain industrial wastewater contains massive grit. Abrasion between grit and stack plates/spiral shafts accelerates component wear. Install screens for pre-treatment to intercept hard impurities. Investigate upstream processes immediately if substantial sediment is detected in filtrate.

Monitor operating torque continuously; avoid waiting for alarms

Track torque readings on the control panel during routine inspections. Gradually rising torque usually indicates sludge buildup on stack plates; increase spray intensity or shut down for cleaning if necessary. Unstable torque fluctuations are generally caused by inconsistent sludge concentration or poor floc formation.

Avoid prolonged overloaded operation

During rainy seasons with increased sludge output, many plants force screw presses to operate at full or overloaded capacity. Long-term overload accelerates wear of transmission systems, back pressure plates and seals, significantly raising failure risks.

3. Common Pitfalls in Routine Maintenance

Online spraying cannot replace thorough disassembly cleaning

Many operators rely solely on continuous spraying without periodic disassembly. Sprays only remove surface sludge, while hardened sludge trapped inside gaps leads to gap deformation over time. Arrange quarterly or annual deep cleaning according to working conditions.

Carry out lubrication on schedule without delay

Grease the reducer, bearings and transmission chains regularly. Maintenance conducted only after abnormal noise appears means irreversible internal wear and higher repair costs. Keep maintenance records of lubrication time and grease specifications.

Inspect consumables regularly; replace them before complete failure

Moving rings, fixed rings, sealing gaskets and back pressure plates are wear parts. Regularly check for deformation, corrosion and warping of stack plates, and calibrate back pressure plate clearance promptly. Mixing new and old rings results in uneven gaps and continuous sludge leakage; replace the full set whenever possible.

4. Protection Measures for Long-term Shutdown

Do not leave the machine unattended after simple rinsing during factory shutdowns or prolonged idle periods.

Standard procedure: Stop feeding and discharge sludge → Thoroughly flush all residual sludge from stack plates → Loosen back pressure plates to release pressure on the spiral shaft.

In humid environments, run the machine briefly at intervals to prevent sludge hardening and component jamming. Drain all pipeline water in cold winter to avoid pipe cracking caused by freezing.

5. Common Misconceptions

❌ Misconception 1: Tighten back pressure plates repeatedly to stop sludge leakage

Blind compression can dry sludge cake temporarily yet sharply increase torque and accelerate component abrasion. Clearance adjustment must match sludge properties.

❌ Misconception 2: Force restart after overload alarms

Repeated forced startup may damage the main shaft and reducer. Shut down first to clear blockages and identify root causes.

❌ Misconception 3: Randomly mix different types of PAM

Cationic and anionic flocculants cannot be mixed. Incorrect chemical selection leads to unsatisfactory dewatering performance regardless of equipment parameter adjustment.

Conclusion

Most screw press faults originate from long-term non-standard operation. Comprehensive control over startup, operation and shutdown plus regular maintenance can drastically cut repair frequency and spare part expenses.

TNW Environmental manufactures TNW series screw dewatering machines, and provides maintenance, emergency repair services for all brands of screw presses as well as wholesale of moving & fixed ring components.

If you encounter problems including sludge leakage, overload and insufficient sludge cake dryness during commissioning or daily operation, contact our technical team for solutions.