Piston pumps rely on ball valves, which must be protected with strainers and yet more valves.back-pressure valves, for example. Foot valves are needed to maintain prime. Valves are prone to clogging and breakdown.

Piston pumps are expensive to maintain, requiring disassembly for cleaning, which can still be difficult to achieve properly; with the result that contamination is a common problem.

Lobe pumps are difficult to clean because of dead spots in the casing. Mechanical seals need swabbing to verify cleaning procedures have been effective. Lobe pumps are not flexible and must be specifically designed for the application. Temperature changes, for example, can result in "galling", where flakes of metal from the lobes are released into the fluid, causing contamination.

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2011-03-22

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