The bailer is a tube with a removable shoe which retains a non-return valve. The valve allows the upward flow of water, mud & sand, but prevents downward flow. Water and materials are retained in the bailer shell for removal after it has been hoisted out of the hole.

The same bailer can be used for surging the screen section of casings to loosen and remove fines and sand to encourage water flow into the well. Bailing is a very good method of determinining the amount of water flowing into a well. and gauging the yield. The surging action as a bailer is pulled up, and then allowed to fall is used to clean out and redevelop existing wells. Surging pulls material from the formation, but does not force it back in. The surging action can be quite severe, and is an excellent means of well development, requiring no additional pumps or compressors; the suction action can be of greater effect than simply pumping or air lifting.

The picture shows the bailer has been totally immmersed in the water and is being used to both to clean out loose material and extend the well depth. In some conditions, the bailer is a very effective drilling tool, giving rapid progress. Different types of valve can be used to assist both drilling and emptying. The shoe can also be modified to give an improved drilling effect by breaking up compacted gravel. Bailers, working inside a casing and screen can be used to "bail down" the casing string in unstable gravel & sands. The casing will sink under its own weight while the bailer removes material from under the leading edge by surging.

Bailers can be made to any convenient length, and can have screw-on extensions to increase the volume. Length is only restricted by the lifting height of the rig, and the way it is set up. The bailer pictured is about 3 metres long and has a capacity of 40 litres. It could be expected to bail at the rate of over 2000 litres per hour. With an extension, the bailing capacity could be raised to over 3000 litres per hour.

Different sized bailers are made to suit the casing in which they are intended to operate. The one pictured is 140mm dia. or 5-inch nominal bore, to suit working within 6-inch casing. Bailers for 4-inch casing would be 90mm outside diameter.

Picture taken in Sierra Leone

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