叠螺式污泥脱水机：结构与工作原理详解Screw-press (volute) sludge dehydrator: structure and working principle

1. Core structure

The body consists of a filter cylinder built from alternating fixed rings and moving rings, with a screw shaft running through it. The screw pitch decreases from the feed end (thickening section) to the discharge end (dewatering section), and a back-pressure plate sits at the outlet.

The moving rings are driven eccentrically by the rotation of the screw shaft, producing continuous relative movement between rings - this is exactly why the machine resists clogging and self-cleans.

2. Working process

• Flocculation: sludge first reacts thoroughly with flocculant (usually cationic PAM) in the mixing tank, forming large flocs.
• Gravity thickening: flocs enter the front of the cylinder and free water drains quickly through the ring gaps under gravity.
• Press dewatering: as the pitch narrows and volume shrinks, sludge is progressively compressed and filtrate continues to escape through the gaps.
• Back-pressure discharge: cake reaches the back-pressure plate, overcomes its resistance and is extruded. Cake moisture is set by the plate gap together with the duty conditions.

3. Why it handles low-concentration sludge

Compared with belt presses and filter presses, the volute gap structure resists blockage, so it can treat relatively low-concentration sludge directly (commonly from around 2,000 mg/L - follow the machine specification), removing the need for a separate thickener tank.

Other characteristics: low speed, low noise and vibration, small rinse-water consumption, continuous unattended operation and a relatively small footprint.

4. Four parameters needed for sizing

• Dry solids load (kgDS/d): the daily dry solids production, the primary basis for sizing. A common calculation is flow multiplied by the difference between inlet and outlet suspended solids, divided by 1,000.
• Feed concentration: too low a concentration forces an oversized model; thicken first if needed.
• Daily operating hours: hourly capacity differs threefold between 8-hour and 24-hour operation.
• Target cake moisture: commonly about 75% to 85%; the stricter the target, the higher the demands on flocculant and operation.

Leave a suitable margin above the calculated value to absorb fluctuations in water quality and future capacity growth.

5. Ancillary equipment

A complete dewatering system usually also includes an automatic flocculant preparation and dosing unit, a feed pump (a progressive cavity pump is common), cake conveying (screw conveyor or belt conveyor), filtrate return piping, a rinse water line and the electrical control cabinet.

6. Troubleshooting

• Cake too wet: check flocculant grade and dose first (the most common cause), then feed concentration, back-pressure plate gap, and wear of the screw flights and rings.
• Turbid filtrate, solids carry-over: poor flocculation - run jar tests to redefine flocculant grade and dose; reduce feed if it exceeds capacity.
• Gap clogging: strengthen upstream screening and grit removal when the feed contains fibres, hair or grit; always rinse before shutdown.
• Poor cake discharge: back-pressure gap too small or cake too dry, screw wear, or a foreign object jamming.
• Abnormal noise or vibration: check bearing lubrication, screw shaft alignment and fasteners.

7. Routine maintenance

• Rinse the cylinder before start-up and always rinse clean before stopping.
• Inspect screw flights and rings for wear periodically.
• Add grease and check gearbox oil at the intervals in the manual.
• Keep flocculant make-up concentration stable to avoid lumps and dosing swings.

Send us the flow, feed concentration, suspended solids data, operating hours and target cake moisture and we will help produce a model recommendation with the accessory list.