Alfa Laval offers several rotary lobe pump ranges, each targeting a different balance of performance, hygienic level and budget. Understanding the distinctions helps you match the right lobe pump to your process line.

SRU — the versatile workhorse

The Alfa Laval SRU rotary lobe pump is available in six gearbox sizes, each with two pump-head displacements. It offers flow rates up to 106 m³/h and pressures up to 20 bar. The universally mounted gearbox lets you switch between vertical and horizontal porting by repositioning the foot. Rotor options include stainless-steel tri-lobe, stainless-steel bi-lobe and non-galling-alloy bi-lobe — the latter providing tighter clearances and higher volumetric efficiency on lower-viscosity products. Temperature ratings range from 70 °C to 200 °C depending on rotor clearance selection.

OptiLobe — cost-effective and EHEDG certified

The Alfa Laval OptiLobe range targets general applications that require gentle product treatment and easy service. Five gearbox sizes provide flow rates up to 77 m³/h at pressures up to 8 bar. Like the SRU, the OptiLobe switches easily between vertical and horizontal porting. It is certified by EHEDG as fully CIP cleanable and conforms to 3-A with FDA-compliant media-contacting components.

SX and SX UltraPure — hygienic and aseptic rotary lobe pumps

The Alfa Laval SX pump range uses a four-lobe (multi-lobe) stainless-steel rotor optimised for maximum efficiency, reduced shear and smooth pumping. Seven gearbox sizes deliver flow rates up to 115 m³/h and pressures up to 15 bar. All media-contacting elastomers are controlled-compression joints that prevent leakage to atmosphere. The SX is EHEDG certified, 3-A compliant and FDA conforming.

For pharmaceutical and biotech processes, the SX UltraPure variant adds USP Class VI elastomers, ASME BPE and GMP compliance, and a complete Q-doc documentation package with full material traceability. This makes it the go-to positive displacement rotary lobe pump for high-purity liquid handling.

Rotary lobe pumps serve a broad spectrum of hygienic process industries. Their ability to pump shear-sensitive media, handle suspended solids and operate bi-directionally makes them indispensable in complex production lines.

Upstream and downstream process integration

In a typical dairy process line, a rotary lobe pump sits between storage or balance tanks and downstream process steps such as pasteurisation, separation or filling. It replaces centrifugal pumps whenever the fluid viscosity exceeds approximately 800 cP, or when shear-sensitive products such as yoghurt and cultured cream must maintain their texture. During fermentation in breweries, rotary lobe pumps transfer yeast at low speeds — typically 100 to 400 rev/min — to preserve delicate cell structures.

In confectionery production, Alfa Laval rotary lobe pumps handle chocolate, biscuit cream, glucose and fruit-pie fillings with particulate matter. Heated or cooled pump casings are available for temperature-sensitive products that could crystallise or solidify. For pharmaceutical lines, the SX UltraPure meets the stringent demands of validation, qualification and process control, backed by its Q-doc documentation.

How requirements differ by industry

Dairy and food plants prioritise EHEDG or 3-A certification and CIP cleanability. Pharmaceutical buyers need full material traceability according to GMP and ASME BPE, plus USP Class VI elastomers. Confectionery and sugar operations focus on handling highly viscous, sometimes abrasive products with heated casings and hard seal faces. Breweries value low-shear, bi-directional flow. In every case, a lobe pump delivers the controlled, volumetric displacement these industries depend on.

For more insight into how pumps support cleaning processes, see our guide on CIP pumps and cleaning in place.

Operating principle and key components

A rotary lobe pump is a positive displacement pump. It directly displaces fluid from the inlet port to the outlet port in discrete volumes. Two counter-rotating rotors turn inside a precision-engineered rotor case. A gear train housed in the pump gearbox synchronises the rotors so they never touch each other or the casing — this non-contact design eliminates metal-to-metal wear inside the pump head.

As the rotors separate at the inlet side, an expanding cavity forms. Atmospheric or system pressure forces fluid into this cavity. The fluid is then carried around the rotor-case wall in the space between the rotor dwell and the casing interior. When the rotors mesh again at the outlet side, a diminishing cavity displaces the trapped volume into the discharge port. Each revolution delivers a fixed displacement, which is why flow rate scales linearly with speed.

The main components of a rotary lobe pump are:

Rotor case — the stainless-steel housing that forms the pumping chamber together with the rotor-case cover. Product-wetted surfaces are typically AISI 316L or Werkstoff 1.4404.

Rotors — available in tri-lobe (SRU, OptiLobe), bi-lobe (SRU) or multi-lobe (SX) profiles. Material is AISI 316L stainless steel or, for applications demanding tighter clearances, non-galling alloy ASTM A-494.

Gearbox — contains the timing gears that synchronise rotor rotation. Stainless-steel construction (AISI 304) supports hygienic external finish.

Shafts — support the rotors through the gearbox bearings. Duplex stainless steel (AISI 329 / grade 1.4462) is used on SX models and higher-pressure SRU configurations for added strength.

Mechanical seals — single, single-flushed or double-flushed variants protect against leakage. Seal-face materials include carbon, stainless steel and silicon carbide, paired with EPDM, FPM or FFPM elastomers depending on duty.

How to select the right rotary lobe pump

Choosing the correct lobe pump for your process line depends on several factors. The table below summarises the key decision criteria.

Viscosity is the single most important parameter. At viscosities above roughly 1,000 cP, volumetric efficiency can reach 95–99 %, meaning almost all theoretical displacement converts into actual flow. At low viscosities and higher pressures, internal leakage (slip) increases, and speed must rise to compensate. In such cases, a circumferential piston pump like the DuraCirc may offer better efficiency thanks to its closer clearances.

Temperature influences rotor clearances. The SRU range offers three clearance settings — 70 °C, 130 °C and 200 °C — so the pump can be matched to both product temperature and CIP temperature. The SX uses a single 150 °C rating. Always confirm that the maximum CIP cycle temperature falls within the pump's clearance rating.

Solids handling varies by rotor form. Bi-lobe rotors (SRU) allow the largest particle sizes — up to 37 mm on the SRU6/353. Multi-lobe rotors (SX) handle up to 28 mm on the largest frame. Tri-lobe rotors on the OptiLobe manage up to 16 mm. When pumping shear-sensitive media such as yeast or yoghurt, keep speeds between 100 and 400 rev/min to avoid cell damage.

Rotary lobe pump compared to alternative approaches

A lobe pump vs gear pump comparison highlights several differences. External gear pumps can be compact and efficient on clean, low-viscosity fluids, but they generally lack the hygienic certifications (EHEDG, 3-A) that process industries require. Internal gear pumps handle higher viscosities but are less suited to fluids with particulate matter. Rotary lobe pumps excel on both counts — they combine gentle solids handling with certified hygienic design.

Compared to circumferential piston pumps (e.g. the Alfa Laval DuraCirc), rotary lobe pumps are typically more cost-effective for medium-viscosity, moderate-pressure duties. Circumferential piston pumps outperform on low-viscosity, high-pressure applications because their closer clearances minimise slip. Twin screw pumps (e.g. the Alfa Laval OS) offer the widest process flexibility, handling both product and CIP in one unit, but at a higher price point.

In short, the rotary lobe pump occupies the middle ground — robust enough for demanding duties, gentle enough for sensitive products, and certified for the strictest hygienic environments.