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Explanation about the pump configurations within the API 610

The purpose of this article is to give you a explanation about the pump configurations within the API 610. The API is an abbreviation for American Petroleum Institute. It is the main U.S trade association for the oil and natural gas industry, representing about 400 corporations involved in production, refinement, distribution, and many other aspects of this industry. Centrifugal pumps are among the most common rotating equipment found in these industries. That’s why the American Petroleum Institute created a standard for this: the API 610.

API 610 provides a classification for various types of centrifugal pumps. The API 610 pumps are primarily divided in three groups: OH, BB and VS.

OHOverhung pumps – The impellers of these pumps protrude from the bearings. The support has to take care of all forces, e.g. the overhung mass and the rotor dynamic and hydraulic forces. The impellers of these pumps can be mounted either horizontally or vertically.

BBBetween bearing pumps – The impellers of BB pumps are suspended in between the supports. For all pumps of this type, the impeller is placed horizontally, in plane with the bearings.

VS – Vertically suspended pumps – VS pumps are supported above the medium to be pumped. The vertically oriented impellers are suspended below the support and are submerged into the medium.


(OH) Flexibly coupled – pumps feature a separate bearing assembly, in addition to the motor. Flexible couplings are usually used to transmit torque from one shaft to another when the two shafts can be slightly misaligned. They can accommodate angular misalignments up to 3° and parallel misalignment to a certain degree. In addition, they can also be used for vibration damping or noise reduction. In rotating shaft applications, a flexible coupling can protect the driving and driven shaft components (such as bearings) from the harmful effects of conditions such as misaligned shafts, vibration, shock loads, and thermal expansion of the shafts or other components.

(OH) Rigidly coupled –  pumps also feature a separate bearing housing. Rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts then hold the flanges together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined together. Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling’s performance as well as its life.

(OH) Close coupled –  pumps are directly mounted on an extended motor shaft. Therefore, no separate bearing assembly is needed and all forces are taken care of by the bearings in the motor. This type of construction is practical to do to dispense with the alignment problem. (OH5)

Horizontal – At right angles to the vertical; parallel to level ground.

Vertical – being in a position or direction perpendicular to the plane of the horizon.

(OH) In-line – a pump whose suction and discharge branches are arranged in line for direct installation into the pipework; special foundations are unnecessary, and the absence of shaft couplings eliminates alignment problems

(OH) Foot-mounted – A pump casing that is provided with feet designed for fastening the pump onto a fundamental or base plate

(OH) Centerline supported – The pump is supported on the centerline of its casing which provides for even thermal expansion on each side of the pump casing support (OH2)

(OH) Bearing bracket – These pumps have a bearing housing integral with the pump to absorb all pump loads. The driver is usually mounted on a support integral to the pump. (OH3)

(OH) High-speed integral geared – These pumps have a speed-increasing gearbox integral with the pump. The impeller is mounted directly to the gearbox output shaft. There is no coupling between the gearbox and pump; however, the gearbox is flexibly coupled to its driver. The pumps may be oriented vertically or horizontally.


(BB) 1 & 2 stage – One or two impellers and associated diffusers or volutes and return channels if required.

(BB) Multistage – A pump with three or more  impellers and associated diffusers or volutes and return channels if required. (BB3) (BB4) (BB5)

(BB) Axial split – Split of the pump casing with the principal joint parallel to the shaft centerline. (BB1) (BB3)

(BB) Radially split  Split of the pump casing with the principal joint perpendicular to the shaft centerline. (BB2)

(BB) Single Casing – The portion of the pump that includes the impeller chamber and volute / diffuser. This part contains a single part and is not enclosed in a pressure case or barrel. (BB4)

(BB) Double Casing – type of pump construction in which the pressure casing is separate from the pumping elements contained in the casing.
The function of the second casing in a BB construction is to resist higher pressures. NOTE Examples of pumping elements include diffuser, diaphragms, bowls and volute inner casings. (BB5)


(VS) Single Casing  The portion of the pump that includes the impeller chamber and volute / diffuser. This part contains a single part and is not enclosed in a pressure case or can. (VS1) (VS4) (VS5)

(VS) Double Casing – type of construction where the pump is enclosed in a second casing with a closed bottom, forming a liquid container. This effectively substitutes the wet pit, that is needed for single casing vertically suspended pumps, but still features the NPSH advantages of a submerged pump. (VS6)

(VS) Discharge through column – The discharge of the pump goes thru the same column pipe as the driven shaft for the impeller. (VS1)

(VS) Separate discharge – The discharge of the pump is a separate pipe than the column pipe where the driven shaft for the impeller goes thru. (VS4) (VS5)

(VS) Diffuser – A diffuser are stationary vanes, fitted in a diffuser casing . They convert velocity into pressure energy and guide the fluid to the impeller vanes of the subsequent stage (VS1) (VS6)

(VS) Volute – A volute is a spiral-like form such that as the liquid is discharged from the impeller into the volute casing, the volute areas increase at a rate proportional to the discharge of liquid from the impeller and a constant velocity exists around the periphery of the impeller

(VS) Axial flow The fluid is pushed in a direction parallel to the shaft of the impeller, that is, fluid particles, in course of their flow through the pump, do not change their radial locations.

(VS) Line shaft – A line shaft is the rotating shaft part of a system of mechanical couplings between the power source the driver and the impeller. (VS4)

(VS) Cantilever –  a cantilever design in which only the impeller and casing are submerged in the tank or sump. All joints, including seals, bearings, bushings, and suction check valves, are located out of the fluid. This design is ideal for moving slurries and abrasive solutions that could degrade or interfere with submerged joints. (VS5)


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American Petroleum Institute

API, an acronym for the American Petroleum Institute, is an organization that develops technical standards for oil and natural gas industries. API 610 is the centrifugal pump standard put forward by API.

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