API 610 - VS2 Pumps
Wet pit, vertically suspended, single-casing axial-flow pumps with discharge through the column shall are referred to as pump type VS3.
VS2 pumps are a vertical, suspended, single-casing diffuser (or volute-type) centrifugal pump design defined within API 610, the leading standard for centrifugal pumps used in petroleum, petrochemical, and gas industry services. VS2 pumps are engineered for high reliability, stable hydraulic performance, and safe operation in demanding process environments.
Design Characteristics of an API 610 VS2 Pump
Vertical Suspended Construction
VS2 pumps feature a vertically suspended bowl assembly with a surface-mounted driver (typically an electric motor). The pump shaft is supported at the driver end by a thrust bearing, while intermediate sleeve bearings support the shaft within the pump column.
Single-Casing, Diffuser or Volute Type
The bowl section is usually a diffuser-type casing, although volute-style designs also exist. This casing converts velocity energy to pressure efficiently while maintaining smooth hydraulic behavior.
Flexible Shafting with Line Shaft Bearings
A multi-piece line shaft transmits power from the motor down to the impeller. Bearings—often product-lubricated or externally flushed—ensure alignment, reduce vibration, and support reliable operation in long-settings.
Surface-Mounted Driver
The motor remains dry and accessible, simplifying maintenance and alignment. Thrust bearings in the driver absorb the full hydraulic axial load.
Suction Beneath the Bowl Assembly
With the pump inlet submerged, VS2 pumps provide strong NPSH characteristics, making them ideal where low suction head or vapor pressure concerns exist.
Where API 610 VS2 Pumps Are Used
VS2 pumps are commonly deployed in:
- Petroleum storage terminals – tank transfer, stripping, loading
- Refineries and petrochemical plants – light hydrocarbon service, condensate recovery
- Pipeline and booster applications – when vertical installation avoids flooding or saves space
- Tank farm operations – including sump, drain, and emergency transfer
- Cooling water and utility services – where vertical orientation suits pit or sump installation
Their vertical configuration makes them well suited for deep sumps, above-ground tanks, or areas where horizontal pumps cannot be installed due to limited footprint or suction conditions.
Performance & Reliability Considerations
1. NPSH Advantages
The submerged impeller significantly improves NPSH available, reducing risk of cavitation—critical for volatile hydrocarbons and hot liquids.
2. API 610 Compliance
API 610 imposes requirements for:
- shaft stiffness and critical speed margins
- bearing life and load handling
- vibration limits
- material classes for corrosive or high-temperature service
- allowable nozzle loads
- rotor dynamics and wear ring clearances
This results in a pump capable of long continuous service in harsh environments.
3. Maintenance & Serviceability
VS2 pumps are designed for:
- easy motor removal without disturbing the column
- accessible shaft couplings for inspection
- robust wear parts for extended service intervals
- stable long-shaft operation under varying hydraulic conditions
4. Material Selection
Depending on the service fluid, materials may include carbon steel, 316SS, duplex stainless steels, or high-alloy options for corrosive or sour service per API 610 material classes.
Why Operators Choose VS2 Pumps
VS2 pumps are preferred when:
- space is limited but deep-well or tank access is needed
- low NPSH conditions prevent use of horizontal pumps
- high reliability is required under API 610 standards
- hazardous or flammable fluids require safe, compliant operation
- long service life with minimal vibration and shaft deflection is essential
In short, an API 610 VS2 pump provides a robust, dependable solution for vertical hydrocarbon-transfer duties where safety, stability, and long-term performance are non-negotiable.
