Submersible vs. Lineshaft
Vertical Turbine Pumps:
Advantages and Limitations
BY ALLAN R. BUDRIS
Several of my past Water World columns have cov- ered vertical turbine line-shaft pumps (VTP; see Fig. 1) and the unique reliability issues that can
arise under various conditions, in addition to actions that can
be taken to minimize these negative factors.
These unique negative line-shaft VTP reliability issues include
the excessive vibration that can result from the flexible motor/
discharge head, and the spaghetti-like line shafting that connects the motor to the below ground liquid end pump bowl
assembly. This is in addition to shaft straightness issues and potential line-shaft bearing problems, which can be lubricated by
either the fluid pumped or by an oil tube feed from the surface.
I’ve covered various positive/corrective actions in these columns, such as finite element analyses, sub-critical line-shaft
bearing spacing, superior bearing materials and lubrication
methods. I did not, however, address the possibility of an alternate pump construction to address these line-shaft VTP issues.
A submersible motor driven vertical turbine pump (see Fig. 2)
has the motor located below the pump bowl assembly, which
eliminates the line-shaft, line-shaft bearing, and motor pedestal components — and therefore the associated vibration/
There are, however, advantages and disadvantages with both submersible motor,
and line-shaft, vertical turbine pump types,
depending on the specific application and
pump construction. The major pluses and
minuses for these two pump types are detailed below.
ADVANTAGES OF A SUBMERSIBLE
Submersible motor vertical turbine
pumps use a submersible motor coupled
to the lower portion of a submerged vertical turbine pump so that both are located
together in the well.
A submersible motor VTP is generally
silent, which is an advantage for heavily
congested metropolitan areas. The above-
ground motor that drives a line-shaft VTP
can at times generate unacceptable noise levels and is less
Since a submersible motor VTP does not have tall, aboveground, discharge heads/motors and line shafting, it is not
susceptible to potential vibration problems from these components. Short set line-shaft VTPs, with low pressures/axial
thrust values are more susceptible to vibration issues than
deep set line-shaft pumps, especially in conjunction with a
variable speed drive.
In some cases, a submersible motor VTP will have a lower intitial cost
since it does not have any line shafting or motor pedestals. However,
submersible motors require power
cables, which can offset the line shaft
cost and could be damaged.
Also, due to not having line shafting and bearing spacing to worry
about, submersible motor VTPs can
operate at higher speeds, which
means fewer pump bowl stages and
a small diameter well casing, both of
which can further reduce initial costs.
Submersible motor VTPs are more
compact and easier to handle, and a
submersible motor VTP does not need
a pump house to protect an aboveground motor from the weather.
ADVANTAGES OF A LINE-SHAFT VTP
Line-shaft VTPs do have some definite advantages over submersible motor VTPs. A submersible VTP motors
is less efficient than an aboveground
motor because of its smaller (
non-optimum) diameter and the possibility of the motor being fluid filled
with a dielectric oil. I’ve conducted
four comparisons that showed the
average submersible motors to be 6. 2
percentage points less efficient then
the aboveground motors (93.7 per-
Figure 2: Submersible
Motor Vertical Turbine