Not all fluids can be moved through a pump without consequence. For water, acids, alkalis, and most low-viscosity chemicals, the mechanical forces generated by a centrifugal or gear pump are inconsequential — the fluid enters, is moved, and exits unchanged. For a growing range of industrially important fluids, this is not the case. Certain fluids respond to the mechanical energy of pumping by breaking down: emulsions separate, polymer chains fragment, cell membranes rupture, or particle structures are destroyed. These are shear-sensitive fluids, and the pump type used to move them determines whether the fluid arrives at its destination intact or permanently damaged.
What Shear Sensitivity Means
Shear is the force applied to a fluid when different layers of it are made to move at different velocities relative to each other. In a centrifugal pump, the impeller spins at high speed and subjects the fluid to intense shear forces as it accelerates from the centre of the impeller to the outlet. In a gear pump, the meshing of gear teeth creates localised zones of very high shear. In a screw pump, the shear is lower but still significant at the contact points between the screw flights and the casing.
A shear-sensitive fluid has internal structures — polymer networks, emulsion droplets, biological cells, or loosely bound particle aggregates — that are disrupted or destroyed when subjected to these forces. Once disrupted, the structure does not recover. The damage is permanent.
Which Fluids Are Shear-Sensitive
The category is broader than many engineers initially assume. Polymer solutions — particularly long-chain polymers used as flocculants in water treatment — lose viscosity and performance when their polymer chains are sheared and fragmented. Oil-in-water and water-in-oil emulsions, including cosmetic creams, food emulsions, and some lubricant formulations, separate or coarsen when subjected to high shear, producing a product that is out of specification. Biological suspensions including cell cultures, yeast slurries, and fermentation broths contain living cells whose membranes are damaged by high shear, reducing viability and yield. Loosely structured aggregates such as flocculated sludge, latex suspensions, and certain paint pigments can be permanently broken down by high shear, producing a finer, less functional dispersion.
In food production, shear sensitivity is a common concern with sauces, dressings, dairy products, and any product where texture is determined by an emulsion or gel structure. In chemical manufacturing, polymer solutions, adhesives, and specialty coatings fall into this category. In water treatment, flocculant polymer solutions are routinely damaged by pump shear, reducing their effectiveness and increasing chemical dosing costs.
Why AODD Pumps Are the Preferred Solution
An air-operated double diaphragm pump moves fluid by the reciprocating action of two flexible diaphragms driven alternately by compressed air. The fluid is drawn into one chamber as the diaphragm retracts and pushed out of the other chamber as the opposing diaphragm advances. The action is gentle, progressive, and entirely free of the rotating components — impellers, gears, screws — that generate high shear in other pump types.
The maximum shear experienced by the fluid in an AODD pump is at the check valves, where the fluid is briefly accelerated through the valve seat. This shear is localised, brief, and orders of magnitude lower than the shear generated by a centrifugal impeller at equivalent flow rates. For the vast majority of shear-sensitive fluids, AODD pumping is gentle enough to leave the fluid structure intact through the entire pumping cycle.
AODD pumps also handle high-viscosity fluids well — the diaphragm action can move thick, viscous materials that would stall or cavitate a centrifugal pump — and they are inherently self-priming, able to run dry without damage, and capable of handling entrained solids or fibrous material that would damage gear or impeller mechanisms. These characteristics make them broadly applicable across the range of process industries where shear sensitivity is a concern.
Fluimac AODD Pumps for Shear-Sensitive Applications
The Fluimac range of AODD pumps covers a wide variety of body materials, diaphragm materials, and size configurations to suit different chemical compatibilities, flow rates, and pressure requirements. For shear-sensitive applications, the correct diaphragm material selection is important alongside the pump design: PTFE for chemically aggressive fluids, Santoprene for general-purpose applications, and other elastomers where specific compatibility is required.
For industrial and process applications in Malaysia where fluid integrity through the pump is a critical requirement, Fluimac AODD pumps provide the combination of gentle pumping action, material versatility, and operational reliability that shear-sensitive fluid handling demands.
To discuss pump selection for your specific fluid and application, contact us at info@autoflotechnology.com.