My vacuum pump oil has turned milky white — what does it mean and can I save the pump?

Milky oil is water in the oil. The oil and the water have been whipped into an emulsion inside the pump chamber, and the pump is now running without a continuous oil film. The pump is usually still savable if you act in the same shift; what kills it is running it for weeks in that state.

Do this first, before changing anything: close the inlet, open the gas ballast fully, and let the pump run warm against a blank for 30 to 60 minutes. Gas ballast admits a controlled amount of air part-way through compression so that water vapour leaves with the exhaust instead of condensing into the oil. On a mild case the oil clears and you have found both the problem and the cure.

If it does not clear, drain it hot. Hot oil carries the water and the sludge out with it; oil drained cold leaves the worst of it sitting in the bottom of the reservoir. Refill, run for an hour, and drain again if the second charge discolours — a single flush rarely gets it all.

Then find where the water came from, because the oil will go milky again otherwise. The three usual sources are: pumping a wet process without gas ballast open, a chamber or line that was never dried after cleaning, and a cooling coil or heat exchanger leaking into the gas path. A pump that emulsifies within days of an oil change is telling you the process is wet, not that the oil was bad.

Judge the damage by what happens after the flush. If ultimate pressure comes back to spec, you got there in time. If it stays high, the vanes and the stator bore have already worn — water-emulsified oil is a poor lubricant and vane wear accelerates quickly. At that point a service kit alone will not restore performance; the vanes need measuring.

Send us the pump model, the serial number, the process gas and how long it ran milky. We will quote the oil, the service kit and, if the wear is beyond a kit, tell you so rather than sell you a kit that will not fix it.