The timing gears, which are not in the wetted end. They hold the rotors in phase so the rotors never touch. As they wear, backlash grows and the rotors drift together - and when they finally contact, the damage takes out rotors and often the casing at once.

Increasing noise and vibration are the early signs, and measured backlash is the definitive check. Gearbox oil condition and any metal in it are the other indicator. Because the gearbox is dry and out of sight, this check is regularly skipped, which is why rotor contact failures still happen.

By measuring clearances at strip-down - rotor to rotor and rotor to casing - against the manufacturer's limits. A rotor can look perfectly serviceable and still have lost enough material to cost significant capacity and priming performance, so visual inspection alone is not sufficient.

Normal elastomer ageing and compression set, chemical attack from the product or from cleaning chemicals, and heat. Cover O-rings are the usual first leak point and are a routine consumable. Where a seal fails repeatedly and early, the cause is usually chemical or thermal rather than mechanical.

No. Replacement elastomers on a sanitary pump must carry the same food-contact compliance as the originals, with documentation, because the hygiene system depends on it. A generic ring that fits perfectly is still a compliance failure and will be picked up at audit.

Worn bearings let the shafts deflect under load, and that deflection closes the running clearance between rotors and casing. A bearing failure therefore often presents as rotor contact damage, and replacing rotors without addressing the bearings simply repeats the failure.

Rebuild is usually economic while the casing bore is within limits, since rotors, seals, bearings and gears are all replaceable. Once the casing itself is worn or scored by a contact event, the cost of restoring clearances rises steeply and replacement becomes the better option.