A peristaltic pump moves fluid by compressing a flexible tube with rotating rollers. As each roller sweeps along the tube, it pinches it shut and pushes a slug of fluid forward — the same mechanic your esophagus uses to swallow. The pumped fluid only ever touches the inside of the tube, never the pump mechanism. That single property makes peristaltic pumps dominant wherever contamination, sterility, or chemical compatibility matters.

How it works: A rotor with 2–4 rollers (or "shoes") rides against a curved raceway. The tube is trapped in the gap. Each roller creates an occlusion — a fully closed pinch — that traps a fixed volume between itself and the next roller. Rotation carries that volume from inlet to outlet. Flow is proportional to RPM, so speed control is trivial: it's a positive displacement pump with a linear flow-vs-speed curve down to a single drop per minute.

Why engineers reach for them:

• No seals, no valves, no contamination: The fluid path is a single disposable tube. Swap tubes between batches — no CIP cycle, no cross-contamination.
• Self-priming and dry-run tolerant: The occlusion always holds, so the pump lifts fluid from below and survives running empty.
• Handles nasty fluids: Slurries, abrasives, shear-sensitive cells, corrosive acids, blood. If it fits in the tube, it pumps.
• Reversible and metered: Reverse the motor, reverse the flow. Count rotations, count volume.

Real-world example: Every dialysis machine uses peristaltic pumps to move a patient's blood through the dialyzer and back. The blood touches only sterile disposable tubing — the pump itself is never sterilized. IV infusion pumps, lab dosing systems, brewing transfer pumps, and concrete admixture dosers all rely on the same principle.

Flow rule of thumb: Volume per revolution ≈ tube cross-section × occluded arc length between two rollers. For silicone tubing with 6 mm ID and a 100 mm arc between rollers on a 2-roller head:

• Slug volume ≈ π × (3 mm)² × 100 mm ≈ 2.8 mL per roller pass
• At 2 rollers × 60 RPM → ~340 mL/min

Watch out for: Tube fatigue is the killer. The tube is a wear part — it work-hardens, cracks, and eventually ruptures. Life is measured in roller passes, not hours. Silicone gives long life for benign fluids; Tygon, Norprene, and PharMed trade flexibility for chemical resistance. Also: pulsation. Two-roller pumps pulse hard; three or four rollers smooth it out at the cost of tube life. And check discharge pressure — most peristaltic pumps top out around 2–4 bar before tube collapse becomes irreversible.