API 610 (Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries) is the reference standard for centrifugal pumps in hydrocarbon service. Before a datasheet gets to dimensions, materials or performance curves, it identifies the pump by a short type code — OH2, BB3, VS6 and so on. Knowing what that code means lets a buyer sanity-check a quote before it is even opened.
The three pump families
API 610 groups every centrifugal pump configuration into three families, based on where the bearings sit relative to the impeller:
OH — Overhung
The impeller is mounted on the end of a shaft that is supported by bearings on one side only (overhung), outside the pumped fluid. This is the simplest, most compact arrangement and covers the majority of single-stage process pumps in a plant.
BB — Between bearings
The impeller (or impellers, for multistage pumps) sits between two bearings, one on each side. This arrangement handles higher heads and supports multistage designs, making it the standard choice for high-pressure and high-head services such as boiler feedwater and pipeline boosting.
VS — Vertically suspended
The pump is mounted vertically, often with the impeller and part of the shaft suspended down into a sump, tank or barrel below grade. Used where the liquid source is below the pump's mounting level, such as vertical turbine or canned/barrel pumps for tank farms and cooling water intakes.
Overhung (OH) sub-types
| Type | Configuration | Typical use |
|---|---|---|
| OH1 | Horizontal, foot-mounted | General process service, lower cost |
| OH2 | Horizontal, centerline-mounted | The default single-stage refinery/process pump |
| OH3 | Vertical in-line, rigidly coupled | Where floor space is limited |
| OH4 | Vertical in-line, rigidly coupled, close-coupled | Compact in-line installations |
| OH5 | Close-coupled, vertical in-line | Small, compact services |
| OH6 | High-speed integral gear pump | Specialised high-head, low-flow duties |
Between-bearings (BB) sub-types
This is the family most buyers of boiler feedwater, pipeline and high-head process pumps deal with directly:
| Type | Configuration | Typical use |
|---|---|---|
| BB1 | Single stage, axially split casing | Moderate head, easy maintenance access |
| BB2 | Single stage, radially split casing | Higher pressure single-stage duty |
| BB3 | Multistage, axially split casing | High-head services such as boiler feedwater, pipeline boosting |
| BB4 | Multistage, radially split casing | Very high pressure multistage duty |
| BB5 | Multistage, radially split, double casing (barrel) | Highest pressure and temperature duty, where a barrel design contains pressure independently of the inner stack |
Vertically suspended (VS) sub-types
VS pumps range from single-casing diffuser and volute designs (VS1, VS2) through axial flow (VS3), line-shaft sump (VS4) and cantilever (VS5) designs to double-casing barrel-mounted vertical turbine pumps (VS6, VS7), used for deep sumps, cooling water intakes and tank farm transfer where NPSH available at grade would otherwise be insufficient.
What API 610 requires regardless of type
Whichever type code applies, API 610 imposes a common set of mechanical and testing requirements that go well beyond a general industrial pump standard:
- Bearing life — confirm the required rated life and load basis against the specified edition and purchaser requirements
- NPSH margin — a defined margin between NPSH available and NPSH required at the rated point
- Mechanical seals per API 682, with the seal flush plan (e.g. Plan 11, 23, 32) specified for the service
- Coupling per API 671 for special-purpose services, with a coupling guard
- Baseplate design suitable for grouting and alignment, with provision for jacking bolts
- Hydrostatic and performance testing to the agreed standard and acceptance criteria, with witnessing defined in the purchase order
Because requirements differ between the 10th, 11th and 12th editions, always confirm the exact edition referenced in your project specification before finalising a datasheet — a pump built to an older edition may not satisfy a newer one on bearing life, seal chamber dimensions or testing scope.
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Frequently asked questions
What does the API 610 type designation (e.g. BB3) mean?
The first two letters describe the bearing arrangement — OH (overhung), BB (between bearings) or VS (vertically suspended) — and the number identifies the specific configuration within that family, such as casing split (axial vs radial) and number of stages. BB3, for example, is a multistage pump with an axially split casing.
Which API 610 type is used for boiler feedwater service?
High-head, multistage boiler feedwater duty is typically served by BB3 (axially split, multistage) or BB4 (radially split, single casing) or BB5 (double-casing/barrel) pumps, depending on the discharge pressure. BB3 is common up to moderate-high pressures; BB5 barrel pumps are used where discharge pressure is high enough that an axially split joint is no longer suitable.
Is API 610 mandatory, or can a pump comply with a similar in-house spec?
API 610 itself is a voluntary industry standard, but most oil, gas and petrochemical operators reference it directly in their procurement specifications, so in practice it is a de facto requirement for critical pump services. Always confirm the exact edition (e.g. 11th or 12th) your project specification calls for, since requirements have tightened between editions.
Does API 610 cover the motor and coupling as well as the pump?
API 610 sets requirements for the coupling (typically referencing API 671 for special-purpose couplings) and for baseplate design, but the driver itself is usually specified separately — API 541 or API 547 for motors — while API 610 focuses on the pump, its bearings, seal chamber and testing.
