Durable Twin-Screw Pumps for Handling Viscous and Chemically Aggressive Fluids

Chemical processing systems often need to transfer fluids that are difficult to pump consistently. High viscosity, poor lubricity, corrosive characteristics, suspended impurities, temperature changes, and fluctuating pressure can all place additional demands on fluid-handling equipment. In these applications, selecting a pump based only on nominal flow is rarely sufficient.

A twin-screw pump provides a positive-displacement conveying principle that can address many of these requirements within a properly engineered chemical processing system. The non-contact screw arrangement allows the pump to handle selected fluids with limited lubricity or corrosive characteristics, while variable speed and reversible operation provide flexibility for different stages of production.

For chemical solutions and complete equipment systems, the pump should be considered together with storage tanks, mixing vessels, pipelines, valves, heating or cooling equipment, filtration, and other process units. The objective is to create a transfer system that remains stable as product properties and operating conditions change.

Why Chemical Fluids Require a Different Pumping Approach

Chemical fluids can behave very differently from conventional low-viscosity liquids. Some remain relatively free-flowing, while others become highly viscous or difficult to move as concentration, temperature, or formulation changes.

Some process media may also have poor lubricating properties. In a conventional pump design, inadequate lubrication between moving components can increase wear or restrict the range of suitable applications.

The SLGP twin-screw pump addresses this challenge through two screws that rotate without direct contact with each other or the pump casing. Product is transported through continuously formed cavities as the screws rotate, creating a positive-displacement conveying action.

This design can be applied to selected chemically aggressive or poorly lubricating fluids when the wetted materials, seals, temperature, pressure, and operating conditions are appropriately specified.

Non-Contact Screws for Demanding Fluid Transfer

The absence of direct contact between the screws and pump housing is an important characteristic when handling fluids that do not provide effective lubrication.

Instead of relying on sliding contact to transfer the product, the twin screws create a controlled conveying volume inside the pump chamber. This allows the pump to handle fluids across a broad viscosity range while reducing direct mechanical contact between the primary rotating components.

The stated viscosity capability of the SLGP series extends up to 500,000 cSt. This figure should be evaluated together with the selected pump model, screw configuration, operating speed, pressure differential, and product temperature. A pump suitable for a highly viscous chemical formulation at one operating point may require a different configuration when the process conditions change.

The same principle applies to corrosive media. Pump material selection and seal compatibility must be matched to the actual chemical composition rather than assuming that one construction is suitable for every chemical product.

Managing Viscosity Across the Process

Viscosity can become one of the main variables in chemical fluid transfer. Concentration, temperature, formulation, and mixing conditions may all affect how easily a product moves through the process line.

The SLGP pump provides a broad speed range, with the overall design capable of reaching up to 3,600 rpm. This gives process engineers flexibility to adjust the transfer rate according to the actual fluid condition.

However, maximum speed is not necessarily the optimum speed for a high-viscosity chemical product. A suitable operating point should consider suction conditions, required flow, pressure differential, product temperature, pipeline resistance, and the selected screw geometry.

This approach allows the pump to become part of a controlled process rather than simply acting as a high-capacity transfer device.

Handling Fluids with Poor Lubricity or Impurities

Certain chemical process fluids may contain impurities, suspended particles, or components that make conventional pumping more complicated.

The SLGP design can accommodate particles up to 40 mm in diameter under suitable conditions. Actual capability depends on particle hardness, concentration, shape, viscosity, screw configuration, and other process variables.

This can make the twin-screw principle relevant to selected chemical formulations containing suspended or soft solid particles.

The non-contact screw arrangement is also useful when the product itself provides limited lubrication. Instead of requiring the process fluid to act as a lubricant between contacting components, the screws operate with clearance between the rotating elements and surrounding surfaces.

Reversible Operation for Integrated Chemical Systems

Chemical production systems frequently involve multiple transfer stages. A pump may need to move material from a preparation vessel to a holding tank, circulate product through process equipment, or assist with recovery from a transfer line.

The SLGP pump supports forward and reverse operation by changing the direction of shaft rotation. This allows the conveying direction to be changed without mechanically rebuilding the pump.

For complete chemical processing equipment, reversible operation can provide additional flexibility when connecting multiple vessels or managing product recovery. It may also help simplify certain circulation arrangements where the same pump needs to serve more than one process direction.

The actual system configuration should determine how reverse operation is used, particularly when valves, filters, heat exchangers, or other directional components are included in the line.

Building the Pump into a Complete Chemical Processing Solution

A chemical pump rarely works as an isolated component. Its performance depends heavily on the surrounding equipment.

A complete system may include raw-material tanks, mixing vessels, dosing equipment, sanitary or process piping, valves, filtration units, heating or cooling systems, intermediate tanks, and filling or packaging equipment.

The twin-screw pump can be positioned within this system to provide controlled transfer between process stages. Variable speed can help accommodate different production requirements, while reversible operation can provide additional flexibility for selected transfer and recovery sequences.

For highly viscous fluids, the relationship between the pump and suction pipeline is particularly important. A long or restrictive suction line can increase resistance before the product reaches the pump. Tank outlet geometry, pump position, pipe diameter, product temperature, and valve selection should therefore be evaluated as part of the complete engineering design.

Temperature and Pressure Influence Pump Selection

Chemical products can change significantly with temperature. Some become easier to transfer when heated, while others require strict temperature control because their chemical or physical properties may change outside a specified range.

The SLGP pump is specified for media temperatures up to 130°C under the stated product configuration. Cleaning temperatures can reach 140°C, where the selected construction and operating conditions permit.

The pump can also be configured with standard or jacketed construction. A jacketed arrangement can be considered when maintaining product temperature around the pump is important for stable processing.

Pressure is another key selection factor. The supplied product information specifies a maximum differential pressure of 16 bar for applicable configurations. Actual operating pressure must be determined according to the selected model and complete system conditions.

Seal Selection Matters in Chemical Applications

Chemical compatibility extends beyond the pump casing and screws. Shaft seals are directly exposed to the operating environment and therefore need to be selected according to the fluid, temperature, pressure, cleaning conditions, and chemical compatibility requirements.

The SLGP series can be configured with single mechanical seals, double mechanical seals, rubber shaft seals, or packing seals.

The appropriate sealing arrangement depends on the specific process. For chemically aggressive fluids, engineers should evaluate the compatibility of all wetted materials and sealing components with the actual chemical formulation rather than selecting the seal solely according to pressure or temperature.

A System-Level Approach to Chemical Fluid Handling

Durability in chemical pumping is not determined by pump construction alone. Reliable operation depends on matching the pump to the fluid and integrating it correctly into the complete process.

The SLGP twin-screw pump provides several useful characteristics for demanding chemical applications: non-contact screw operation, positive-displacement conveying, broad viscosity capability, variable speed, reversible flow, and flexible sealing configurations.

For chemical solutions and complete equipment systems, these features can support the transfer of viscous, poorly lubricating, or selected chemically aggressive fluids when the pump materials and operating conditions are correctly specified.

The most effective selection process begins with the actual chemical properties and process requirements: viscosity, chemical compatibility, temperature, pressure, solids content, required flow, suction conditions, and cleaning method. From there, the pump configuration, screw geometry, seals, materials, and surrounding equipment can be matched to create a reliable fluid-handling system rather than treating the pump as a standalone component.