Pump Families and Configurations

Two ways to move a liquid

Pumps fall into two families. A centrifugal pump (a rotodynamic pump) adds velocity to the liquid with a spinning impeller and turns that velocity into pressure. Its flow changes a lot when the system resistance changes. A positive displacement pump traps a fixed volume and pushes it out on every stroke or turn. Its flow stays almost the same when the pressure changes, so it must never run against a closed valve without a relief valve.

Centrifugal pumps are the most common pumps in process plants, water treatment and building services because they are simple, smooth and handle large flows. This course is about them, but you need to recognise the difference, because the rules for safe operation are not the same.

Centrifugal configurations

The petroleum, petrochemical and gas industry standard from the American Petroleum Institute, API 610, groups centrifugal pumps by configuration. Other industries use similar names. Three main groups exist:

• Overhung (OH): the impeller is on the end of the shaft, beyond the bearings. Examples include the end-suction pump (OH1, foot mounted; OH2, centreline mounted) and vertical in-line pumps.
• Between bearings (BB): the impeller or impellers sit between two bearing housings. Examples include axially split casings (BB1, BB3) and radially split barrel pumps (BB5) for high pressure.
• Vertically suspended (VS): the pump hangs into a sump or a can, such as a vertical turbine pump.