Full casing of bore well is recommended for long life of bore and pump. It prevents the pump from getting stuck due to loose boulders, stones, soil and silt. It also reduces chances of accident due to protruding stones and boulders at the time of removing the pump and pipe.
Prevention of Water Hammer
At the time of pump stoppage, water recedes/falls at tremendous speed from a height. Especially in deep bore wells of about 500 ft & above, this creates enormous pressure and load on the pump and bottom most pipe called as water hammering. For such deep bore wells, it is recommended to make a 3mm hole in the pump NRV to protect the pump and pipe from water hammering.