Most AODD pump specifications stop at chemical compatibility and pressure rating. When the fluid being transferred is a flammable solvent, that is not enough. The casing material’s electrical conductivity — or lack of it — determines whether static charge generated by fluid movement has a discharge path to ground, or accumulates until it finds one on its own. When it finds its own path, it may do so as a spark.
Conductive plastic casings exist specifically to solve this problem, and in flammable solvent applications and ATEX-rated environments, they are not optional.
How Static Charge Builds Up in Plastic Pump Casings
Fluid moving through a plastic casing generates static electricity through the triboelectric effect — contact and separation between the fluid molecules and the plastic surface creates charge separation. In metal pump casings, this charge dissipates immediately through the metal body to the grounded pipework and frame. In standard plastic casings — polypropylene, PVDF, acetal — the casing is an electrical insulator. The charge has nowhere to go.
As fluid continues to flow, charge accumulates on the plastic surfaces and in the fluid itself. The rate of charge generation depends on fluid resistivity, flow velocity, and the turbulence of the flow through the pump’s wetted path. Low-conductivity fluids — organic solvents such as hexane, toluene, acetone, IPA, ethyl acetate — are among the worst for static charge generation precisely because they do not conduct the charge away as polar solvents and aqueous solutions do.
When the accumulated charge exceeds the breakdown voltage of the surrounding air or vapour, it discharges as an electrostatic spark. In a normal environment, this is a nuisance. In an environment where flammable vapours are present — as they almost certainly are when you are pumping solvents — it is an ignition source.
What “Conductive” Actually Means for Plastic Materials
A conductive plastic is a standard polymer matrix — PP, PVDF, or similar — loaded with conductive additives, typically carbon black or carbon fibre, during the moulding process. The additive creates a conductive network through the polymer matrix, giving the material a surface and volume resistivity in the range of 10⁴ to 10⁶ ohms — sufficient to provide a continuous discharge path for static charge without compromising the material’s chemical compatibility or mechanical strength.
The critical distinction is that the chemical compatibility of conductive PP is essentially the same as standard PP, and conductive PVDF performs identically to standard PVDF in chemical service. Choosing conductive material does not require trading chemical resistance — it adds grounding capability to an otherwise unchanged material specification.
Conductive plastics are not the same as antistatic plastics. Antistatic materials reduce surface charge accumulation by modifying the surface energy to attract moisture — they provide limited and humidity-dependent protection. Conductive plastics provide a direct, permanent discharge path regardless of humidity conditions. For ATEX-rated environments and flammable fluid applications, only conductive — not antistatic — materials are acceptable.
The Grounding Path Must Be Complete
A conductive pump casing is necessary but not sufficient. For static charge to discharge safely to earth, there must be a continuous, unbroken conductive path from the fluid inside the pump, through the casing, through the pipework connections, and to a verified earth point.
This means every component in the path must be conductive or bonded. A conductive pump casing connected to standard PVDF piping through a plastic union provides no protection — the conductive casing cannot discharge through the non-conductive pipe. In solvent transfer systems designed for ATEX compliance, conductive plastic piping or metal pipework with proper bonding straps is required throughout, not just at the pump.
Bonding and earthing are distinct. Bonding connects all conductive elements of the system together so they are at the same potential — preventing sparks between components. Earthing connects the bonded assembly to a verified earth point, discharging the accumulated static to ground rather than allowing it to build. Both are required. Bonding without earthing still allows the entire system to accumulate charge together and discharge to an unconnected element or person.
How to Verify Groundability
Verifying that a pump installation is correctly grounded is a simple resistance measurement. Connect one probe of an ohmmeter to the earth point and the other probe to the fluid path — typically through the pump inlet connection. The resistance should be below 10⁶ ohms (1 megohm). Above this value, the conductive path is insufficient for reliable static dissipation.
If the measurement fails, check each connection in the path systematically — pump to pipework connection, pipework to earthing strap, earthing strap to earth point. The failure is almost always at a threaded connection where non-conductive thread tape (PTFE tape) has been used to seal the joint, breaking the conductive path. Use conductive thread sealant, or metal compression fittings without PTFE tape, at all connections in the grounding path.
Periodic re-verification is necessary. Vibration and thermal cycling can loosen connections and increase contact resistance over time. Include a grounding continuity check in your regular maintenance schedule for all solvent transfer systems.
When to Specify Conductive Casing
The criteria are straightforward. Specify conductive casing whenever the fluid has a flash point below 60°C, or whenever the operating environment is classified as Zone 1 or Zone 2 under ATEX or IECEx. Flammable solvents — hydrocarbons, alcohols, ketones, esters, ethers — almost all fall below the 60°C threshold. If you are uncertain about your fluid’s flash point, treat it as requiring conductive material until confirmed otherwise.
For aqueous process fluids, acids, alkalis, and other polar chemicals without significant vapour pressure at operating temperatures, standard plastic casing is generally acceptable. The triboelectric effect is less severe, the fluid’s conductivity assists charge dissipation, and there is no vapour to ignite. Where there is any doubt, confirm with your facility’s safety and electrical classification documentation.
The Fluimac Phoenix range is available in conductive PP and conductive PVDF configurations for solvent and ATEX applications. The conductive versions carry the same model designations with a -C suffix and are dimensionally identical to the standard versions — grounding capability is added without requiring pipework modifications or changes to service procedures.
Related reading: PVDF Material for AODD Pumps: When to Specify It and Why It Matters, Why Diaphragm Material Matters More Than Casing Material in Aggressive Chemical Transfer, PVDF AODD Pump: When Is It the Right Choice of Material?.
If you are handling flammable solvents and are unsure whether your current AODD pump installation meets the grounding requirements for your site classification, contact Autoflo at info@autoflotechnology.com. We can help you review the full path from pump to earth point and confirm compliance.