Two rotors turn towards each other inside a casing, carrying fluid round the outside from inlet to outlet. External timing gears keep them in phase so they never touch each other or the casing. The close clearance between them forms the seal, and no surfaces rub.

Because nothing rubs, so no wear particles enter the product and the fluid is not sheared. Delicate products, fruit pieces and emulsions pass through intact. Sanitary designs also have no dead legs and strip quickly, so they can be cleaned in place to the standard those industries require.

Comparatively large ones. The open cavities between the rotors pass particles that would jam a gear or vane pump, which is why they are used for products containing fruit pieces, meat chunks and similar. The limit is set by the cavity size and by whether the solid can survive the passage undamaged.

Because the seal is a clearance rather than a contact. A thin fluid slips back through that gap from the high-pressure side to the low, and the thinner the fluid the more slips. Lobe pumps therefore work best on medium to high viscosity and lose capacity noticeably on water-like liquids.

Never. The fluid lubricates the clearance between rotors and casing, and without it the surfaces contact, gall and destroy the running clearances within moments. Dry-run protection is a standard fitting where the supply can be interrupted, and it is far cheaper than a rotor set.

Moderate compared with gear or screw pumps, because the clearance seal leaks more as pressure rises. Higher-pressure duty requires tighter clearances, which reduces solids handling and temperature tolerance. Where high pressure and thin fluid coincide, a different pump family is the correct answer.

Within limits, yes - they will draw a suction lift once wetted, which suits emptying tanks and totes. Priming performance depends on the clearances and on the fluid, and a worn pump primes noticeably worse, which is often the first symptom of wear that anyone notices.

Gear pump teeth mesh and contact, which seals better and handles higher pressure but shears the fluid and wears against it. Lobe rotors never touch, so they are gentler and cleanable but seal less well. Gear pumps suit oils and hydraulics; lobe pumps suit products that must not be damaged.

Fewer lobes give larger cavities and better solids handling with more pulsation; more lobes give smoother flow and better sealing with smaller passages. Bi-wing and tri-lobe are the common patterns, and the choice follows whether solids or flow smoothness matters more for the product.

Yes - reversing rotation reverses flow, which is useful for clearing a line or draining back to a tank. Note that reversing also reverses the pressure loading on seals and bearings, so sustained reverse running should be confirmed with the manufacturer rather than assumed from the fact that it works.