I am answering my own question as I have had this kind of experience with my publications.I feel that may be sometimes the revised version sent to the reviewers are not taken seriously hence the delay may be due to their pre-commitments and not able to attend and comment on the revised articles.It is however the responsibility of the editor to take quick decision and send to other reviewers.They should understand the plight of authors waiting for decision after 2-3 revisions. Moreover the scientific information gets diluted and loses its signification after delayed publications