Hygienic and aseptic circumferential piston pumps

Alfa Laval offers two circumferential piston pump families that cover standard hygienic and aseptic duties. Choosing between them depends on your cleaning regime, sterility requirements, and operating pressure.

The DuraCirc range spans five gearbox frame sizes (30–70) with a total of thirteen volumetric displacements, whilst the DuraCirc Aseptic is available in five pump head sizes. Both share the same gearbox platform, so upgrading from standard to aseptic configuration requires no pipework changes. All media-contacting elastomers use controlled-compression joints to prevent leakage to atmosphere.

For applications where a hygienic centrifugal pump cannot deliver the required discharge pressure or where shear-sensitive handling is essential, a positive displacement piston pump is the preferred choice.

In which industries is a circumferential piston pump used?

Where do piston pumps fit in your process line?

Piston pumps typically sit between a supply vessel or balance tank and downstream process stages such as heat exchangers, fillers, mixers, or pressurised storage tanks. Upstream, the pump draws product through a suction line — often under flooded-suction conditions — whilst downstream it pushes the fluid through valves, pipework, and other resistance elements at the required discharge pressure.

Because circumferential piston pumps generate flow that is largely independent of system back-pressure, they maintain a stable flow rate even as line conditions change. In a typical dairy or beverage line, a DuraCirc circumferential piston pump can replace or complement a centrifugal pump where higher pressures or viscous products exceed centrifugal capabilities. It connects to the same standard port fittings (ISO/DIN clamp or flange) and can be driven by a geared electric motor with a frequency converter for variable-speed operation. During CIP cycles, a differential pressure of 2–3 bar across the pump is recommended to promote effective cleaning.

For aseptic lines, the DuraCirc Aseptic provides sterile barrier flushing, making it suitable for installation after UHT treatment or sterile filtration stages. Hygienic pumps in these positions must withstand SIP temperatures of approximately 145 °C and provide validated seal integrity — requirements that the DuraCirc Aseptic meets through its integrated flush housing and controlled-compression elastomers.

What is a piston pump?

A piston pump is a type of positive displacement pump that moves fluid by trapping a fixed volume in a chamber and displacing it from inlet to outlet. In the context of hygienic process industries, the term most commonly refers to circumferential piston pumps — rotary units in which two winged rotors (pistons) rotate around the circumference of a channel in the pump casing. Each rotation generates a partial vacuum at the suction port, drawing fluid into the chamber, and then displaces it into the discharge port as the rotors re-mesh.

Unlike reciprocating piston pumps found in hydraulic or high-pressure industrial systems, circumferential piston pumps operate with smooth, low-pulsation flow. The rotors are synchronised by a gear train in the gearbox and never contact each other, the casing, or the casing cover. This non-contact principle reduces wear, keeps the pump CIP-capable, and protects shear-sensitive products such as dairy cream or yoghurt.

Circumferential piston pumps matter in hygienic pump applications because they combine high pressure capability (up to 40 bar) with high volumetric efficiency across a broad viscosity range. Their construction from AISI 316L stainless steel and FDA-conforming elastomers ensures compliance with 3-A, EHEDG, and other international hygiene standards, making them a dependable choice for food, dairy, beverage, and pharmaceutical processing.

How does a conventional and a circumferential piston pump work?

A conventional (reciprocating) piston pump uses a piston moving back and forth inside a cylinder. On the intake stroke the piston retracts, creating a low-pressure zone that opens an inlet valve and draws fluid into the cylinder. On the discharge stroke the piston advances, closing the inlet valve and forcing fluid out through a discharge valve. This action produces pulsating flow and requires check valves to control direction.

A circumferential piston pump works on a fundamentally different principle. Two wing-shaped rotors are mounted on parallel shafts and driven by a synchronised gear train so they contra-rotate without touching. As the rotors un-mesh at the suction port, an expanding cavity generates a partial vacuum that pulls fluid into the pump. The fluid is then carried around the circumference of the casing channel by the rotor wings. When the rotors re-mesh at the discharge port, the fluid is displaced into the outlet. The result is smooth, nearly pulse-free flow in either direction — reversing the drive shaft rotation reverses the flow.

This rotary displacement method eliminates the check valves and pulsation dampeners that reciprocating units need. Combined with the close running clearances of the non-galling alloy rotors, it delivers the high volumetric efficiency and gentle product handling that dairy, food, and beverage processors require.

What are the differences between a circumferential piston pump and a gear pump?

Both circumferential piston pumps and gear pumps belong to the positive displacement family, yet they differ significantly in rotor geometry, clearance design, and suitability for hygienic applications. In a gear pump, two meshing gears trap fluid between gear teeth and the casing, then carry it from inlet to outlet. Internal and external gear variants exist, but both rely on close metal-to-metal mesh contact.

A circumferential piston pump uses two wing-shaped rotors (pistons) that contra-rotate within a channel in the pump casing. The rotors are synchronised by a gear train in the gearbox, so they never touch each other or the casing. This non-contact design eliminates metal-to-metal wear in the pump head, extends service life, and makes the pump fully CIP-capable — a requirement that conventional gear pumps struggle to meet.

Key practical differences include pressure capability, shear, and cleanability. The Alfa Laval DuraCirc circumferential piston pump reaches up to 40 bar discharge pressure and maintains 95–99 % volumetric efficiency at viscosities as low as 15 cP, thanks to its non-galling alloy rotors with very small clearances. Gear pumps can achieve similar pressures but typically generate higher shear and are harder to clean to hygienic standards. For dairy, food, and beverage processes where product integrity and sanitary compliance matter, circumferential piston pumps are the preferred choice.