PIPES IN PARALLEL
When a main pipeline divides in to two or more parallel pipes, which may again join together downstream and continue as main line, the pipes are said to be in parallel.
The pipes are connected in parallel in order to increase the discharge passing through the main. It is analogous to parallel electric current in which the drop in potential and flow of electric current can be comp ared to head loss and rate of discharge in a fluid flow respectively.
The rate of discharge in the main line is equal to the sum of the discharges in each of the parallel pipes.
The flow of liquid in pipes (1) and (2) takes place under the difference of head between the sections A and B and hence the loss of head between the sections A and B will be the same whether the liquid flows through pipe (1) or pipe (2). Thus if D1, D2 and L1, L2 are the diameters and lengths of the pipes (1) and (2) respectively, then the velocities of flow V1 and V2 in the two pipes must be such as to give