Selection criteria for VS2, VS3, and VS7

The VS2 pump is the designation given by API Standard 610 and ISO Standard
13709 to a vertically-suspended single stage  pump. The VS3 is the designation
given to a similar vertically-suspended, single stage, axial flow pump, and the VS7
is the designation given to double-casing volute-type pump.

The VS2, VS3, and VS7 pumps are used in applications requiring low differential
head and where the normal net positive suction head (NPSHA) is inadequate for
the required flow rate and anticipated pump speed, hence there is a need to
locate the impeller below the ground level so that additional NPSHA can be
gained from the pump setting.

The criteria for specifying or selecting a VS2, VS3, or VS7 pump are clear-cut
because the pumps are very distinct from one another, and there is very little room
for overlap. The only things these three pump designations have in common are
that they are vertically-suspended, and are of single stage (or single casing)

The VS2 and VS3 pumps are designed for wet fit or sump installation and operate
in an open-loop system. They are used mainly for pumping water (and other
non-hazardous liquids) such as in irrigation system, dewatering, flood control,
cooling tower, or in city or municipal water supply system. They are usually built
with light casing because they operate with low working pressure.

The VS7 pump is designed for installation inside a barrel and operates in a
closed-loop system. It is used for pumping a variety of liquids including
flammable, toxic, and other hazardous liquids. Depending on its design suction
pressure, a VS7 pump may be made of heavy casing (or bowl assembly) to
handle higher working pressure.

The VS2, being a volute pump, can only be either of the radial flow or mixed flow
design. The VS3, being an axial flow pump, can only be either of the propeller, or
axial, pump design. Thus, the required flow rate, differential head, and pump
speed (or, in other words - the pump specific speed) will determine whether the
pump selection will be that of a VS2, or VS3, pump. The low to medium pump
specific speed will fall within the operating range of the VS2, whereas the high
pump specific speed will fall within the operating range of the VS3 pump. The VS3
can be built with its discharge nozzle either at above, or below, the ground surface.

File: pump API designation2

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