EP 1110-1-27
27 Jan 00
(3) Submersible vs. lineshaft installations. In general, submersible models are more versatile but
characteristically provide less wire-to-water efficiency than many lineshaft turbine models. Lineshaft
installations offer the advantage of having the motor at the surface, where it is accessible, heavy motors
for very large pumps are not suspended downhole, and motors are less expensive to repair. Disadvantages
of lineshaft installations include:
The need for a lineshaft and its associated bearings which require lubrication and are
vulnerable to wear, especially in aggressive, biofouling water.
The need to use steel column pipe, which is subject to rapid corrosion.
Restricted access at the surface for drawdown measurement and other access to the well
casing.
Greater skill is needed in lineshaft pump repair, and wells must be very straight and plumb.
Surface-mounted motors must be protected from weather and heated or cooled as needed.
(4) Achieving a balance of equipment features. As exact matches to conditions and ideals may not
be possible, pump choice may be a balance of features. In general, the highest efficiency pump models
should be used. Exceptions occur where service is so severe that short operating lifespans can make more
expensive, tunable pumps not cost-effective to operate. In these cases (particularly where efficiency
differences are minor), low-priced but serviceable pumps that can be discarded and replaced or cleaned
may be the better option.
c. Computers and controllers. Automated water-level and flow information facilitates data
analysis and planning. Devices exist to provide "real time" water-level and flow measurements without
personnel being onsite. SCADA systems originally developed for process treatment can be adapted for
well fields, permitting rapid, easy, and continuous monitoring of well and pump hydraulic performance,
and even physical-chemical changes. Pump controllers help to maintain regular current flow of the proper
characteristics and phase to pump motors, thereby prolonging motor life and shielding motors from line
surges. All pump motors should be equipped with automatic controllers.
d. Suction flow control. One technology that has developed in recent years is the refinement of the
controlled-inflow pump tailpipe referred to as a suction flow control device (SFCD). These simple
devices are perforated pump intake pipes. The perforations are made in a pattern that forces flow to enter
the well in a more cylindrical fashion (Nuzman 1989 and Ehrhardt and Pelzer 1992), instead of
An upward-faced cone pattern typical of pumped screened wells in which almost all flow
enters through the top 10 to 15% of the screen when the pump is above the screen.
Preferentially at the point where the pump is located within the screen, typical of many
HTRW pumping wells.
Unfortunately, practical commercial access to the best quality devices is at present still limited to Europe
and the Mediterranean, and inclusion in U.S. site planning has to await commercial availability in this
country.
e. Well and water system modifications to facilitate maintenance. A maintenance-friendly
wellhead setup is important to minimize the difficulty of performing maintenance. Issues include meeting
limits to avoid confined space designation, making the well seal secure but removable, and discharge
head and instrument connections easy to detach. Table 9-1 provides recommendations for wellhead
features to facilitate maintenance.
9-2
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