For any water system indicate the velocity of flow for flushing process ?

For pipe lines which are not flushed since long need high velocity more than5 fps in start and then2 -4 fps later. Normal flushing velocity is2-4 fps

since the accumulation of chemicals on to the pipe stagnates the initial velocity of flushing would be around6 feets per seconds but generally if its a new system it would around around2.5 to4 feet per second.