Depamu Customized Automatic Industrial Single Screw Pump for Liquids of Various Viscosity
Abstract
Industrial fluid handling is increasingly defined by variability — feedstocks shift, product formulations change, and a single production line may be called upon to move fluids ranging from water-thin condensates to semi-solid pastes within the same shift. Centrifugal pumps, the traditional workhorse of fluid transfer, lose efficiency sharply once viscosity exceeds approximately 300 cSt, with documented head losses of 8 meters or more and efficiency reductions of 20% at viscosities approaching 800–1,000 cP. Above this threshold, positive displacement technology becomes the rational choice. Among positive displacement designs, the single screw pump — also known as the progressive cavity (PC) pump — has emerged as the reference technology for viscous, solids-laden, and shear-sensitive media. Depamu (Hangzhou) Pumps Technology Co., Ltd., founded in 2003 and drawing on advanced German engineering principles, has developed a platform of customizable, automation-ready single screw pumps engineered for precisely this operational reality: liquids of various viscosity, handled reliably and precisely across the full industrial spectrum. This article examines the technical foundations, customization dimensions, and automation capabilities that position the Depamu single screw pump as a viscosity-agnostic solution for modern process industries.
1. The Viscosity Challenge and the Case for Positive Displacement
Viscosity is not a single operating point; it is a continuum. In petrochemical operations alone, a refinery may process crude slates whose physical properties vary from thin condensates to vacuum residues exhibiting viscosities exceeding 100,000 cP at ambient temperature. Pulp slurries in paper manufacturing range from 3% to 18% consistency, with viscosities that can surpass 1,000,000 mPa·s. Toothpaste, a non-Newtonian fluid, typically falls between 30,000 and 150,000 cP and carries abrasive particles that challenge conventional pump internals. Sewage sludge combines 1% to 12% solids with grit and fibrous material, producing an abrasive, non-uniform medium whose flow behavior defies simple characterization.
A pump intended for such diversity cannot rely on velocity-based energy transfer. The Depamu single screw pump operates on the positive displacement principle. Its pumping element consists of a precision-machined, single-helix metallic rotor that rotates eccentrically within a double-helix elastomer stator. As the rotor turns, a series of sealed cavities forms along the axis of the rotor–stator assembly; these cavities progress continuously from the suction end to the discharge end, carrying a fixed volume of fluid with each rotation. Because the sealing line between rotor and stator is maintained under both static and dynamic conditions, the pump generates differential pressure without check valves or complex reciprocating mechanisms.
The consequence for viscosity handling is decisive: flow rate is directly proportional to rotational speed and essentially independent of discharge pressure and fluid viscosity. A centrifugal pump confronted with a viscosity increase migrates away from its best efficiency point and may cease to deliver useful flow entirely. The Depamu PC pump delivers the same volumetric displacement per revolution whether the medium resembles water or molasses. This viscosity-independent volumetric behavior is the foundational reason the technology can serve as a single, configurable platform across an exceptionally wide viscosity spectrum — from 1 mPa·s to 1,000,000 mPa·s, and in specific configurations up to 2,000,000 cP.
2. Customization: Engineering the Pump to the Fluid
A single screw pump that is merely “capable” of a wide viscosity range is not the same as a pump that is optimized for a specific duty point. Depamu’s approach to customization begins with the recognition that viscosity, while central, is never the only variable. Solids content, particle size, chemical aggression, temperature, shear sensitivity, and lubricity all interact with viscosity to define the true operating envelope. The customization process therefore addresses four interdependent dimensions: hydraulics, materials, drive, and instrumentation.
Hydraulic and geometric customization. The rotor–stator geometry — pitch length, eccentricity, and interference fit — determines the pump’s pressure capability and its tolerance for solids. Depamu single screw pumps accommodate solids concentrations up to 60% and maximum particle diameters of 10 mm or more in standard petrochemical configurations, with sludge-duty variants capable of conveying incompressible materials up to 80 mm in diameter. For high-viscosity, low-flow metering duties, a longer-pitch geometry may be selected to reduce shear while maintaining pressure; for high-solids sludge, a shorter-pitch, larger-clearance geometry minimizes clogging risk. Flow capacities span 30 liters per hour to 150 cubic meters per hour, with discharge pressures reaching 4.8 MPa or higher depending on configuration, and the platform can be extended to 3,000 m³/h in larger industrial frames.
Materials customization. The stator is the component most directly exposed to the combined effects of viscosity, abrasion, and chemical attack. Depamu offers stator elastomers including nitrile rubber (NBR) for hydrocarbon and general industrial service, and fluoroelastomer (FPM) for elevated temperatures and aggressive chemistries; for particularly aggressive media, PTFE or advanced polymer linings can be specified. Rotors are typically manufactured from stainless steel or specialized alloys, with AISI 316L stainless steel available for wetted components where chloride, sulfide, or organic acid corrosion is a concern. This material matrix allows the same fundamental pump architecture to be deployed in food-grade, sanitary, chemical, and heavy industrial contexts without compromise.
Temperature and environmental customization. Depamu single screw pumps operate across a pumped-fluid temperature range of −12°C to +150°C, covering ambient chemical transfer as well as elevated-temperature process streams. The pumps are self-priming with a suction lift of up to 8 meters of water column, eliminating the need for auxiliary priming equipment and simplifying installation in sump, tank, and pit applications. Flexible mounting configurations and multi-modular structural combinations further allow the pump to be integrated into skid-mounted dosing packages, mobile transfer units, or fixed process lines.
3. Automation: From Transfer Device to Controlled Process Element
The “automatic” dimension of the Depamu platform is not an afterthought; it follows directly from the physics of positive displacement. Because flow rate is proportional to rotational speed, the single screw pump becomes a controllable, repeatable flow source when paired with a variable frequency drive (VFD). A single pump can serve simultaneously as a transfer device and a Metering Pump, eliminating the need for separate flow control valves with their associated pressure drop, erosion, and maintenance burden.
This capability is realized through several levels of automation integration. At the simplest level, VFD control allows manual or remote speed adjustment, providing a turndown range that accommodates changing viscosity without hardware modification. At the next level, closed-loop control uses feedback from flow, pressure, pH, or conductivity sensors to adjust pump speed automatically, maintaining a target flow rate or dosing ratio even as fluid properties drift. Depamu’s dosing packages incorporate programmable logic controllers (PLCs) that can interface with a plant distributed control system (DCS) or host computer, transmitting status and fault signals and accepting remote start/stop and setpoint commands. For polymer dosing in wastewater treatment, where the polymer-to-sludge ratio directly affects both dewatering performance and chemical cost, the PC pump’s pulsation-free, low-shear flow combines with VFD control to deliver precise, repeatable dosing while preserving the molecular integrity of shear-sensitive polyelectrolytes.
The automation capability extends to protection and diagnostics. Dry-run protection and overpressure protection are recommended for dosing duties, preventing damage during abnormal operation. Because wear in abrasive service is influenced by speed, operators can reduce pump speed during high-solids excursions to extend rotor and stator life — an operational strategy that is only feasible when the pump is under variable-speed control.
4. Application Envelope: Viscosity Diversity in Practice
The practical value of a customizable, automated single screw pump is best understood through the range of duties it addresses.
Petrochemical high-viscosity slurry transfer. Depamu stainless steel sanitary single screw pumps handle bitumen, pitch, heavy vacuum gas oil, catalyst slurries, polymer solutions, and oil–water emulsions. The sanitary designation refers to polished product-contact surfaces, absence of dead spaces, and compliance with FDA and EU 1935/2004 materials regulations — design principles that in petrochemical service translate into reduced cross-contamination risk, easier cleaning, and extended service life by minimizing corrosion initiation sites.
Pulp and paper. Pulp conveying demands low-shear handling to preserve cellulose fiber length and final paper strength. The PC pump’s laminar, non-pulsating action moves the fibrous mass without beating or macerating it, while the absence of narrow clearances accommodates long fibrous strands that would clog centrifugal alternatives.
Sewage sludge and polymer dosing. In wastewater treatment, the same pump platform serves two distinct viscosity regimes: abrasive, high-solids sludge transfer from clarifiers to digesters and dewatering equipment, and low-viscosity, shear-sensitive polymer dosing where molecular degradation would compromise flocculation effectiveness.
Food and pharmaceutical high-viscosity products. Toothpaste at 30,000–150,000 cP, with abrasive silica or calcium carbonate particles, requires hygienic construction, precise metering, and gentle handling — a combination the Depamu single screw platform addresses through sanitary materials, VFD-controlled flow, and low-shear cavity transport.
5. Conclusion
The Depamu customized automatic industrial single screw pump is not a single product but a configurable engineering platform built around a stable physical principle: positive displacement through progressing cavities delivers volumetric flow that is independent of viscosity and proportional to speed. Customization — in rotor–stator geometry, elastomer and alloy selection, temperature capability, and mounting configuration — adapts this principle to the specific fluid and process environment. Automation — through VFD control, PLC/DCS integration, and closed-loop feedback — transforms the pump from a passive transfer device into an actively controlled process element capable of maintaining precision as viscosity and other fluid properties vary. For industries where a single pump must move liquids across a viscosity range spanning six orders of magnitude, from water-like to semi-solid, the value proposition is not merely technical capability but operational continuity: one pump architecture, engineered to the duty, controlled to the requirement.