Progressive cavity pump (Progressive cavity pump)

A Progressive Cavity Pump is a positive-displacement pump that uses a helical metal rotor turning inside a double-helix elastomeric stator to convey fluid through a series of sealed cavities that advance axially from suction to discharge. The pump was invented by French engineer Rene Moineau in 1930, giving rise to the alternative name 'Moineau pump,' and is also called PCP, PC pump, or single-screw pump. As the rotor rotates eccentrically, the geometric mismatch between the single-helix rotor and the double-helix stator creates cavities whose volumes remain constant but whose position progresses smoothly along the pump axis. The result is a pulsation-free, near-constant flow that scales linearly with pump speed regardless of discharge pressure (within design limits).

Progressive cavity pumps excel at handling fluids that defeat other pump types: viscous liquids from 1 cP to over 1,000,000 cP, slurries containing up to 30% solids by volume with particles up to 30 mm, shear-sensitive fluids (microbial cultures, polyelectrolyte solutions, soft-floc digestate) that would be damaged by impeller pumps, and multi-phase mixtures with entrained gas. Indian CBG plants use PCPs in virtually every slurry duty: fresh feedstock pumping at 8–12% TS, digester recirculation, dewatered digestate transfer at 20% TS, and FOM slurry handling. The smooth, low-shear delivery preserves digester biology and prevents fibre breakup that would clog downstream separators.

Operational discipline around PCPs centres on three issues. First, stator wear — the rubber stator is the primary consumable, with service life of 6–24 months depending on feedstock abrasiveness; stator replacement cost is Rs 25,000–1.5 lakh per pump and typical Indian plant stocks 90 days of stators. Second, dry-run protection — running a PCP dry burns out the stator within minutes through frictional heat; standard protection includes dry-run sensors (thermistor in the stator), discharge pressure switches, and motor current monitoring. Third, cleaning protocols — fibrous biogas slurry can pack into the cavity during shutdowns, causing high starting torque that trips overloads; standard practice is to flush with water before any shutdown longer than 30 minutes. Indian vendors include Roto Pumps, Tushaco, NETZSCH, Seepex, and Mono — capital cost is Rs 1.5–8 lakh for typical CBG-scale models. PCP operating cost is dominated by stator replacement (60–70% of TCO) and energy (motor efficiency around 80–85% versus 75–80% for centrifugal at same duty), partly offset by the elimination of pre-treatment failures that would otherwise occur with centrifugal alternatives.