Slotted Pipes, Casing Pipes and Screens

Selection Off Screen Diameters
 The designed yield of a tube well is 150m²/h (1.5 Cusecs) and a screen having 20% open area is proposed to be used in a length of 20m to tap an acquifer of 25m thick. Diameter, of the screen is to be worked out.
 As Q = A x V
 
 Where Q = discharge in m²/s, A = effective open area of the screen 
 V = entrance velocity in m/s (to be ltd. to 0.03 m/s) 
 
 Therefore, A = 150/3600 x 1/0.03 = 1.39m² 
 Taking effective area as 50% of that provided, in order to taking into account the reduction of the effective area of the screen opening with time due to incrustation rearrangement of the acquifer particles around the screen and coverage by gravel, etc.

The required open area = 2 x 1.39 = 2.78m² 
 Open area of pipes = x d x l x open area 
 Where d = dia of pipe, l = length of pipe
 Therfore, d = 2.78/ x 20 x 20 = 0.22m or 220mm 
 
 The required sceen dia works out 220mm. 
 
 Selection of Slot Size
 Acquifer Material Classification - The acqifer material may be classified into various categories according to the following ranges of the particle size:

ORDERING DETAILS: