Daihatsu Perodua Engine Manufacturing was already a customer of ours — we had been supplying them Dosatron units for mixing their metalcutting fluid — so when I visited one day and asked, as I usually do, whether they also use AODD pumps, the conversation went somewhere interesting. Yes, they said. And they asked if we had one that doesn’t break down often.
When I asked what was happening, the answer was that their diaphragm was failing repeatedly, with intervals of less than six months. The pump was a 1/2″ SS body unit with a PTFE diaphragm, which is a specification many people would consider the premium choice. PTFE has a reputation in this industry as the safest, most chemical-resistant, most durable diaphragm material — the one you specify when you want the best. It is not an unreasonable instinct. But it turned out to be the wrong one for this application.
What the Pump Was Actually Doing
The application was removing waste oil from the sump of CNC machines, to be collected and disposed of. CNC machining generates metal chips — small, hard fragments of the workpiece material, in this case engine components — and these chips inevitably find their way into the sump along with the cutting oil. The fluid being pumped was not chemically aggressive. It was mechanically aggressive. It was an abrasive slurry, effectively, even if it looked like oil.
PTFE is an extraordinarily chemically inert material. It resists almost every acid, solvent, and oxidising agent you can put through a pump, which is why it has the reputation it does. But chemical resistance and mechanical resistance are different things entirely, and PTFE is notably soft and weak against abrasion. When an abrasive particle passes over a PTFE surface under pressure repeatedly, it wears through it. Metal chips in a sump oil stream do exactly that on every pump stroke — the diaphragm flexes, the fluid moves across its surface, and the chips abrade the material progressively until the diaphragm fails. The less than six months interval they were experiencing is consistent with this mechanism. It was not a chemical compatibility problem. It was a wear problem.
The right material to consider for abrasion resistance is one that is harder and tougher against mechanical wear. NBR (nitrile rubber) is a material that many people associate with “basic” or “entry-level” — if PTFE is perceived as the premium diaphragm, NBR is often perceived as the cheap alternative you use when you don’t want to spend on a proper material. That perception is wrong, or rather, it is only valid when you are evaluating chemical resistance to oils and solvents in combination with mechanical durability. For abrasion specifically, NBR’s rubber elasticity and surface hardness make it significantly more resistant to abrasive wear than PTFE’s relatively soft fluoropolymer structure. The same principle applies to pump body and casing materials: there is no universally superior material, only the most suitable one for the specific chemistry and mechanical conditions of the application.
The Change and the Result
We recommended switching from PTFE to NBR for the diaphragm. The pump body remained SS316, which was appropriate for the application and not the source of the problem. The change was only to the diaphragm material.
That was in 2020. The diaphragm ran for three years without needing replacement — compared to the previous interval of less than six months. Same pump, same installation, same fluid. A different material specification based on what the application actually required.
What This Keeps Reminding Me
The impulse to specify PTFE as the “safe” or “premium” choice is one I encounter regularly, and I understand where it comes from. If you are unsure of the chemistry or want to minimise the risk of a compatibility issue, PTFE is a reasonable default for chemical resistance. But it is only a default for chemical resistance, not for all conditions. There is no diaphragm material — and no pump material generally — that is best in all situations. Every specification needs to start with the actual properties of the fluid and the actual operating conditions: is it chemically aggressive? Is it abrasive? Is it hot? Does it contain solids, and if so, how hard are they?
In this case, the fluid was not particularly chemically aggressive, but it was abrasive. Specifying the most chemically resistant diaphragm and ignoring the abrasion question meant six months of service life where three years was achievable. The material hierarchy is not fixed. It depends entirely on what you are asking the material to withstand.
If you have a pump application involving abrasive fluids — waste oils with swarf, slurries, fluids with suspended solids — and you want to talk through the right material specification for your conditions, reach out to us at info@autoflotechnology.com.