Well Screens

Well Screens

Well screens are used to draw water from aquifers located in unconsolidated materials - such as sand. Simply stated, well screens let the water into the bore hole and keep the sand out.

The well screen, or strainer, forms the "working end" of the water well. Through it flows water from the formation and its characteristics and placement in the bore hole wall in large part govern the efficiency and life of the well.

There are many types of well screens available. The most basic form is perhaps the field or knife slotted pipe still popular in some sections of the country. Its use is restricted, however, because of the lack of uniformity in slotting and the small available open area produced for water entry.

Machine perforated pipe base screen produces uniformity in slotting but to be used as a screen, must be covered by wire gauze or wire rods. This type screen is used in many applications including temporary wells where it may be pulled and reused many times. It is very durable, hard to damage and a driller can easily repair the gauze or wire wrapping.

Machine perforated casing or in some instances sheet material which is rolled after perforating is a popular type of screen for applications where small slot or openings are not required. Some variations include "shutter screens" having closely spaced horizontal louvers, vertical type louvers open on two sides, and "eye lid" louvers. In general these types of screens enjoy their greatest use in gravel wall type construction where small slot openings are not required.

Another distinct type of screen is the vertical rodded wire wrapped screen. A cage of vertical rods are used around which continuous wire is wrapped horizontally. This type screen is available in almost any size slot opening and by varying the number and size of the vertical rods almost any degree of structural strength can be obtained.

In the selection of a screen four basic factors should be considered. These are: 1) a good screen should be structurally strong enough to support the bore hole; 2) it should be resistant to corrosion, 3) it should prevent excessive movement of sand into the well and 4) it should allow entry of water into the well with a minimum of friction.