What is a sealed gearbox on a floor machine?

What is inside it

A single-disc floor machine has to turn a fast motor into a slow, high-torque pad. That reduction happens in a gearbox sitting directly above the pad — the dirtiest, wettest position on the machine. POLIVAC's answer, fitted across the PV25, PV25TS, PV25HC, C25, C25TS, C27, C27RS, A23, A23HS and the Sandivac sanders, is the 'Polidrive': single-reduction helical gears running on deep-grooved ballraces in a housing that is sealed and filled with oil.

Helical gears mesh gradually rather than tooth-on-tooth, which is why POLIVAC describes the result as quiet positive power. Running them in oil inside a closed housing does two things at once: it keeps a lubricant film on the teeth permanently, and it keeps the grit, water and stripping chemical thrown up by the pad on the outside of the casting.

Sealed against what, exactly

Floor machines work in slurry. Stripper is caustic, scrubbing water carries suspended grit, and a sander is surrounded by abrasive dust. Any of the three will destroy an exposed gear train or a bearing running in grease — POLIVAC's own copy on the A23HS puts it as eliminating contamination from dust and chemicals for superior reliability and service life. The sealed housing is what allows the same casting to be scrubbing on Monday, stripping on Tuesday and sanding on Wednesday.

The current Gen2 machines — PV25GEN2, C25 GEN2, C27 GEN2 and the SV25/SV30 Gen II sanders — use a different arrangement to the same end: a triple-planetary HD 6.8:1 helical-cut industrial gear drive, which POLIVAC specifies for grinding and sanding loads.

When it matters

This is a specification to check when you are comparing machines on price and cannot see why one costs more. The gearbox is not visible, it is not on the box, and it is the single component that decides whether a floor machine is still working in fifteen years or is a warranty claim in three. Ask what the gearbox is, whether it is sealed, and what the warranty on it is separately from the warranty on parts — on the PV25 that is two years on motor and gearbox against one year on parts, which tells you where the manufacturer expects failure not to occur.

It matters most on machines that see stripper and slurry: scrubbers, strippers and any polisher that doubles as a scrubber. It matters least on a machine that only ever runs dry on a sealed floor.

What people get wrong is treating a sealed gearbox as a maintenance-free promise for the whole machine. It is not — brushes, pads, the clutch system, the lead and the vacuum still need attention on the normal schedule. The sealed housing removes one failure mode, and it is the expensive one.