Comparing OH and BB Pump Configurations

The following guide from PumpWorks focuses on two widely used horizontal centrifugal pump types: Overhung (OH) and Between Bearings (BB).

API 610 Pump Classifications

API 610 defines three primary centrifugal pump configurations:

• OH (Overhung): The impeller is mounted at the end of a single shaft, cantilevered beyond the bearing housing.
• BB (Between Bearings): The impeller is positioned between two bearings for improved balance and support.
• VS (Vertically Suspended): The impeller and pump shaft are suspended vertically into the pumped fluid.

This article focuses on OH and BB configurations due to their relevance in horizontal installations.

Overhung (OH) Pumps

Description

Overhung pumps feature a design in which the impeller is supported on one end of the shaft. The bearing housing is located entirely outside the process fluid.

OH Subtypes

• OH1: Foot-mounted, end-suction pump with a separate bearing bracket.
• OH2: Centerline-mounted casing with separate bearing housing.
• OH3/OH4/OH5: Vertical inline configurations using close-coupled or separate driver arrangements.
• OH6: Integrally geared high-speed design, often used in light hydrocarbon or gas compression applications.

Benefits

• Smaller installation footprint
• Quicker mechanical seal replacement and inspection
• Preferred in moderate pressure applications with stable hydraulic conditions

Constraints

• Higher shaft deflection risk at large impeller diameters or pressures
• Limited suitability for high flow or elevated temperature systems

Common Uses

• Utility water
• Chemical feed
• Light hydrocarbon transfer

Between Bearings (BB) Pumps

Description

BB pumps place the impeller between bearings, providing symmetrical support and reducing dynamic shaft loading under high-pressure conditions.

BB Subtypes

• BB1: Axially split, single or double suction
• BB2: Radially split, single-stage
• BB3: Axially split, multistage
• BB4: Radially split, multistage with segmental construction
• BB5: Barrel-type, radially split, multistage

Benefits

• Greater shaft stability across varying load conditions
• Better suited for elevated pressures and process temperatures
• Reduced vibration and axial thrust due to symmetrical rotor design

Constraints

• Larger footprint and heavier construction
• Maintenance requires more disassembly, especially in multistage designs

Common Uses

• Boiler feed systems
• Pipeline transport
• Water injection and amine circulation

OH vs. BB Pump Configuration Comparison

Choosing the Appropriate Configuration

Select OH pumps for installations where space is restricted and the process involves clean, low-viscosity fluids under moderate hydraulic load. These pumps are also well-suited when maintenance accessibility is a priority.

Select BB pumps in scenarios involving high differential pressures, elevated temperatures, or flow stability under fluctuating operating conditions. The design accommodates multistage operation and extended run-times in continuous-duty systems.

About PumpWorks

PumpWorks engineers and manufactures API 610 compliant OH and BB centrifugal pumps for the petroleum, chemical, and gas industries. All units are engineered and assembled in the USA and hydrostatically tested in-house.

With decades of application experience and in-house CFD capabilities, PumpWorks offers tailored pump solutions to suit demanding operational conditions. Our field service teams provide inspection, troubleshooting, and lifecycle support.

Contact PumpWorks today to speak with an engineer or request a detailed technical proposal.

Explore some of our API 610 pumps:

• PWH OH2 Process Pump
• PWI OH3/OH4 In-Line Pump
• PWI-D Vertical In-line-Double Suction Impeller
• PWV VS1/VS6 Vertical Pump
• PWD BB1 Single-Stage Double
• PWR BB2 Pump
• PWM BB3 Multi-Stage Split Case Pump
• PWB BB5 Barrel Pump
• PW-11 OH2