The core structural differences between VS4 and VS6
API 610 VS4 vertical submersible pump
VS4 is a vertical suspension, single pump shell structure. The pump body and impeller are immersed in the liquid collecting tank or container, and the medium is transported to the system through an independent discharge pipe. The long shaft is usually supported by guide bearings, with the driver and thrust bearings located above the mounting base.
VS4 is suitable for open or normal pressure collection tanks and is commonly used for the transportation of oily sewage, process drainage, condensate, wastewater and general corrosive liquids. The system layout is relatively simple and there is no need to set up a suction tank. However, as the underwater depth increases, the stability of the long axis, guide bearing lubrication and critical speed must be focused on.
API 610 VS6 vertical barrel pump
VS6 is a double-casing vertical pump. The outer cylinder forms a closed suction flow channel, and the interior usually adopts a multi-stage guide vane structure. The medium first enters the suction cylinder and is then pressurized by the first-stage impeller. Therefore, the liquid column provided by the cylinder can be used to improve the inlet conditions of the first-stage impeller.
VS6 is more suitable for high lift, low NPSH or volatile media, such as liquefied hydrocarbons, light oils, cryogenic liquids, tank output and high-pressure process transportation. Its advantages are stable operation and large head coverage, but the cost of equipment, foundation, cylinder and installation is usually higher than that of VS4.
Comparison of main parameters of VS4 and VS6
Depends on the minimum liquid level and immersion depth
| Comparison project | API 610 VS4 | API 610 VS6 |
|---|---|---|
| Pump casing form | Single pump casing | Double pump casing, with suction cylinder |
| Typical stages | Mostly single stage, can also be designed according to working conditions | Usually multi-stage |
| Suction environment | Open or normal pressure sump | Closed suction cylinder |
| Lift range | Low to medium lift | Medium to high lift |
| Cavitation adaptability | The inlet conditions can be improved through the cylinder liquid column | |
| Typical media | Sewage, drainage, condensate, corrosive liquids | Liquefied hydrocarbons, light oil, low temperature or high pressure media |
| Project investment | Relatively low | Relatively high |
| Maintenance focus | Long shaft, guide bearing, discharge pipe | Multi-stage rotor, cylinder seal and hoisting space |
The specific flow rate, head, temperature, pressure and allowable NPSH should be checked by the manufacturer based on the API 610 version, pump type size and actual medium. The model cannot be determined based only on the general range.
How to choose typical engineering applications?
Refinery waste oil pool or device drainage
If the medium is in a normal pressure sump, the lift requirement is not high, and the pump body is allowed to be directly immersed in the liquid, VS4 is usually selected. When selecting, it is important to confirm sedimentation, particle size and minimum immersion depth.
Liquefied hydrocarbon and light oil transportation
When the saturated vapor pressure of the medium is high and vaporization is easy to occur, VS6 is usually preferred. The suction barrel can improve the inlet pressure of the first-stage impeller, and the closed structure is also more suitable for hazardous media.
Tank output and high-pressure transportation
When the project requires both large flow, medium and high head, and stable and continuous operation, multi-stage VS6 can be selected. The number of stages should be determined based on the total head of the system, pipeline loss and adjustment method. Excessive margin cannot be retained simply by increasing the number of stages.
Chemical waste liquid and corrosive media
VS4 can be considered for atmospheric waste liquid pool, but stainless steel, duplex steel or other corrosion-resistant materials should be selected according to the composition of the medium. If the medium is volatile, toxic or requires closed transport, VS6 should be further evaluated.
Common selection questions
Is VS6 definitely safer than VS4?
Not necessarily. VS6 is suitable for low NPSHA, high head and volatile media, but the structure is more complex and the cost is higher. Using VS6 under normal pressure drainage conditions may result in over-configuration.
Is the longer the submerged length of VS4, the better?
No. Excessive length will increase the risk of shafting deflection, critical speed control and guide bearing wear. The underwater length should be determined based on the minimum liquid level, immersion requirements, number of shaft segments and maintenance conditions.
Can the selection be completed by providing only the flow rate and head?
No. The manufacturer also requires media name, density, viscosity, temperature, vapor pressure, particle conditions, normal and minimum liquid levels, suction vessel pressure, NPSHA, material requirements, operating mode and site power conditions.
Purchasing suggestions and Feiyue Pump solutions
Feiyue Pump can provide API 610 VS4 vertical submersible pumps and VS6 vertical barrel pump selections for oil refining, petrochemical, chemical and storage and transportation projects based on the depth of the liquid collection tank, liquid level changes, medium vapor pressure, system head and on-site installation conditions. Through hydraulic matching, shafting calibration, material selection and cavitation analysis, we help purchasers achieve a reasonable balance between operational reliability, maintenance convenience and project investment.
