To keep loose sand and gravel from collapsing into the borehole, it is necessary to use screened casing pipes. The screen supports the borehole walls while allowing water to enter the well; unslotted casing is placed above the screen to keep the rest of the borehole open and serve as a housing for pumping equipment.
Slots are cut into PVC casings which are primarily close to each other – this is called “Screen” in drilling terminology.
Properties
Screens should have as large a percentage of non-clogging slots collapse as possible, be resistant to corrosion, have sufficient strength to resist collapse, be easily developed and prevent sand pumping.
Application areas
Medium to Deep Boreholes for water applications.
Specifications
Screen / slots have different specifications as per the areas & regions, in Zambia, the slots are mostly 0.8mm to 1mm size with 15mm – 20mm width between each slots.