Seals & Maintenance of Rotary Lobe Pumps: Extending Equipment Service Life in Sanitary Applications

A rotary lobe pump is a positive displacement pump: the two lobe-shaped rotors rotate synchronously in opposite directions driven by a separate timing gearbox isolated from the pump casing. The two rotors maintain a small clearance and do not contact each other, so there is no metal-to-metal friction inside the pump casing, no lubrication is required, and the product is not contaminated by oil. This is why lobe pumps preserve the structure of shear-sensitive fluids (cream, sauce, yogurt) and can handle high-viscosity fluids containing solid particles.

Although the pump casing wears very little, two locations do wear over time. The first is the mechanical seal at the point where the shaft passes through the casing — this is the boundary between the pumped fluid and the external environment, where continuous sliding contact occurs. The second is the rotor clearance: as the rotor edges and the inner casing surface gradually wear, the clearance widens, causing slip (back-flow) to increase and actual flow rate and achievable pressure to drop. Planning maintenance for a lobe pump therefore means monitoring these two components.

The mechanical seal is a deliberate wear component: it is designed to wear gradually and be replaced on a scheduled basis rather than allowing leakage. The OMAC lobe pump range offers several different mechanical seal types depending on application — high-temperature CIP/SIP capability, abrasion resistance for fluids with particles, or compliance with food sanitary requirements. For high-sanitary configurations meeting the 3-A standard on the BA/BB series, OMAC uses the 7KFO seal, combining a self-draining design so that fluid does not accumulate in the seal chamber after cleaning.

One notable point for maintenance is the seal arrangement. The OMAC C/CF series (EHEDG + 3-A + ATEX configuration) uses a front-loading seal: technicians replace the seal from the front of the pump without removing the rotors or disconnecting the pump from the pipeline. This approach reduces downtime and lowers the risk of recontamination when opening the pump — particularly significant for food and pharmaceutical lines that require re-sanitization after every intervention.

Rotor clearance is the gap between the rotor edges and the opposing rotor and the inner casing surface. This clearance is calculated to be small enough to limit back-flow, yet large enough to prevent the rotors from contacting each other during thermal expansion. Over time, the rotor edges and casing surface wear, causing the clearance to widen; the consequence is that at the same rotational speed, actual flow rate and pressure decrease — an early indicator that an overhaul is needed.

For thin, low-viscosity fluids, a widened clearance has a stronger effect (thin fluids slip back through the gap more readily). For high-viscosity fluids the impact is less pronounced, but monitoring is still advisable. The inspection procedure typically involves measuring clearance with a feeler gauge during scheduled maintenance, comparing against the manufacturer’s specified values, and adjusting or replacing the rotors/casing when the limit is exceeded. This should be logged to forecast the replacement schedule rather than waiting until output visibly drops before taking action.

The primary cause of rapid seal failure in sanitary pumps is prolonged dry running. Without fluid, the seal face lacks a lubricating and cooling film, generating localized heat that burns or cracks the seal face within a short time. It is therefore essential to prime the pump adequately before start-up, avoid running the tank dry, and install dry-run protection where risk exists.

Several other operating practices help extend service life: do not allow the pump to run above the design pressure (this creates large axial forces on the seal and rotors); keep CIP/SIP temperatures within the seal material limits; maintain the correct oil type and level in the timing gearbox; and when pumping large solid particles, select the appropriate series that accommodates the particle size rather than forcing the pump to handle oversized objects. Making use of the lobe pump’s reversibility for backflushing also reduces fluid accumulation in the seal chamber.