Selection Guide: How to choose the right W-type single-screw pump for high viscosity solid-containing media?

The structural characteristics of W-type single screw pumps, why can they be adapted to high viscosity solid-containing media?

The core of the W-type single-screw pump consists of a screw and a bushing. The spiral sealing cavity formed by the two is the key to its adaptation to special media. During operation, the screw rotates to push the continuous conveying of the medium in the sealing chamber. This volumetric conveying method can effectively avoid the "slip" or flow interruption problems caused by high viscosity media (such as paste and gelatinous materials) during pumping. At the same time, its runner is smooth and has no complicated corners, which can reduce the collision and retention of solid particles (such as ore powder and fiber impurities) during transportation and reduce the risk of blockage. In addition, the gap between the pump body and the media contact part can be adjusted according to the size of the solid particles, further improving the adaptability to the solid-containing medium, which is also its core advantage that distinguishes it from traditional pump types such as centrifugal pumps and gear pumps.

What are the characteristics of high viscosity solid-containing media that directly affect pump type selection?

The three major characteristics of high viscosity solid-containing media need to be considered carefully and directly determine the selection direction of W-type single-screw pump. First of all, the viscosity range. Media with different viscosity (usually 500-1000000 cP) need to match screws with different pitches and speeds. For example, high viscosity (>1000000 cP) media need to choose large pitch screws to reduce the flow resistance of the medium in the cavity; low viscosity solid media need to optimize the sealing structure to prevent media leakage. The second is the solid particle parameters, including particle size (common 0.1-50mm), concentration (volume proportion of 5%-60%) and hardness. When the particle size is large or the concentration is high, a pump type with a widened flow channel must be selected, and the bushing must be made of wear-resistant materials; particles with high hardness (such as quartz sand) need to strengthen the wear resistance of the screw surface. Finally, the media is corrosive. Acid and alkaline media need to choose contact parts made of corrosion-resistant materials to avoid damage to parts caused by long-term use.

When determining flow and head requirements, what type of selection misunderstandings should be avoided?

Flow and head are the core parameters of W-type single-screw pump selection. If the calculation deviation can easily lead to inefficiency or damage to the equipment, two major misunderstandings need to be avoided. The first misunderstanding is "select according to the maximum flow rate of the theory". In actual working conditions, high-viscosity media will reduce the actual flow rate due to viscous resistance. If selected according to the theoretical value, the actual output of the pump may be much lower than the demand. The theoretical flow rate needs to be corrected based on the media viscosity coefficient (usually, you need to check the viscosity-flow correction curve provided by the pump manufacturer). For example, when the viscosity is 10,000 cP, the actual flow rate may only be 60%-70% of the theoretical value. The second misunderstanding is "ignoring the reasonable setting of the head margin". In the transportation of solid-containing media, the pipeline resistance will increase due to particle friction. If the head is calculated only based on the ideal pipeline, it is easy to cause insufficient actual head of the pump. Usually, the margin of 10%-15% is required based on the calculated value to ensure stable transportation.

For high viscosity solid media, how to choose the material for key components of the pump body?

The key components of the W-type single-screw pump in contact with the medium need to be selected according to the characteristics of the medium to balance wear resistance, corrosion resistance and cost. For non-corrosive, high-hard solid-containing media (such as ore slurry, coal powder), the screw can be quenched with No. 45 steel surface (hardness up to HRC55 or above) or sprayed with tungsten carbide, and the bushing is made of nitrile rubber (NBR) or polyurethane (PU). The former is wear-resistant and elastic, which can reduce the impact of particles on the screw; for weakly corrosive solid-containing media (such as acidic fruit pulp in food processing), the screw can be 304 or 316 stainless steel, and the bushing is fluoroelastic (FKM), which takes into account both corrosion resistance and food safety; for strongly corrosive solid-containing media (such as acid and alkali sludge in the chemical industry), the bushing is made of Hastelloy and polytetrafluoroethylene (PTFE) bushings. Although the cost is high, it can ensure long-term stable operation and avoid leakage or failure caused by component corrosion.

How to match the speed and power of W-type single-screw pump according to the characteristics of the medium?

The reasonable matching of speed and power requires the characteristics of high viscosity solid medium to avoid the problems of "big horse pulling a small cart" or "small horse pulling a large cart". In terms of speed selection, high-viscosity media need to reduce the speed (usually 200-600 r/min), because high-speed rotation will aggravate the internal friction of the medium, causing the pump body to rise, and even destroy the medium structure (such as some polymers); media containing large particles (>10mm) also need to reduce the impact wear of particles on the bushing. Low viscosity solid-containing media can appropriately increase the rotation speed (600-1500 r/min) and improve the conveying efficiency, but it must be controlled within the rated rotation speed range of the pump. Power matching needs to be calculated based on the corrected actual flow, head and medium density. The formula is usually: Power (kW) = (flow m³/h × head m × medium density kg/m³ × gravity coefficient 9.8)/ (3600 × pump efficiency × transmission efficiency). The pump efficiency needs to refer to the performance curve provided by the manufacturer. On this basis, solid media usually require an additional 10%-20% power headroom to deal with instantaneous load fluctuations.

How to pass the trial operation after selection and verify whether the W-type single-screw pump is suitable for working conditions?

The trial operation after the selection is a key step in verifying adaptability. The four major indicators need to be monitored and the deviations are adjusted in a timely manner. The first is the flow rate and pressure stability. It is continuously monitored through the flowmeter and pressure gauge for 30 minutes. If the flow rate fluctuates more than ±5%, the pressure drops sharply or fluctuates frequently, it may be that the gap between the screw and the bushing is improper (too large leads to leakage, too small leads to increase friction resistance), and the gap needs to be disassembled and adjusted. The second is the temperature and noise of the pump body. During normal operation, the surface temperature of the pump body should not exceed the ambient temperature + 40℃. If the temperature is too high, it may be that the speed is too high or the media viscosity exceeds the adaptation range; the operating noise should be controlled within 85 decibels. Abnormal noise (such as metal friction sounds, vibration noise) may be stagnant of solid particles or bearing wear, and the machine needs to be shut down for inspection. Finally, the medium conveying state is to observe whether the outlet media has obvious particles crushing, layering or deterioration. If so, it is necessary to re-evaluate whether the screw structure and speed are in line with the characteristics of the medium to ensure that the conveying process does not destroy the original properties of the medium.