A Guide To Water Well Casing and Screen Selection - 9
 |
5.0 CASING REQUIREMENTS
 |
This section deals with the factors which should be evaluated in the
casing selection, including elements relevant to the casing and screen relationship.
5.1 Diameter
Diameter of the upper pump housing casing must provide sufficient
clearance between the column pipe and casing to permit installation of a sounding tube
or air line to measure depth to water. Extra clearance should be allowed for free
operation of shaft driven pumps and the electric cable for submersible pumps. No well
is exactly straight and operation will be unsatisfactory if there is misalignment.
Additionally, consideration should be given to the possibility of corrosion product
buildup which may lock the bowl to the casing. Consequently, pump housing casing should
have a minimum diameter at least two inches greater than the nominal diameter of the
most efficient pump required for the desired yield.
| PUMP HOUSING DIAMETER SELCTION CHART |
Nominal Bowl
Diameter (Inches) |
Operating Pump
Speed (RPM) |
Yield
(gpm) |
Minimum
Casing I.D. (inches) |
| 8 |
3500
1800
1200 |
200-1200
100-600
160-400 |
10 |
| 10 |
1800
1200 |
200-1500
370-670 |
12 |
| 12 |
1800
1200 |
400-2300
250-1500 |
14 |
| 14 |
1800
1200 |
1000-4500
800-3500 |
16 |
| 16 |
1800
1200 |
2000-5200
1300-3400 |
18 |
| 18 |
1800
1200
900 |
3200-5400
2200-4000
2800-3000 |
20 |
| 20 |
1200
900 |
3100-5500
2300-3600 |
24 |
| 22 |
1200
900 |
7500
5600 |
24 |
For submersible pumps increase minimum I.D. 2 inches. For pump
settings below 400 feet increase minimum I.D. 2 inches.
The chart above serves as a guideline for specification of pump
housing diameter according to production.
While it is true that increasing well screen diameter does not
have much effect on production, there are strong reasons for specifying identical
casing and screen diameters, with the exceptions of telescoped screen installations
and under-reamed gravel envelope well design. Equal internal diameters facilitate well
development and redevelopment processes. The possibility of damage due to dropping a
pump or tools is minimized. Maintaining identical diameters prevents the possibility
of excessive head loss through a restricted tube. Finally, it must be remembered that
wells smaller than six inch diameter are practically impossible to repair and larger
diameters facilitate later deepening if required.
In wells deeper than 1,200 feet, a reduction of four inches in
screen diameter can be practical. This is generally limited to high capacity wells
where the screen diameter is a minimum of 12 inches. The saving in screen and borehole
costs may offset other considerations. This reduction normally begins at the bottom of
the pump housing case.
Back |
R & D Home |
Next