Here is my flowchart and I want to add labels L1,L2, and L3 to the bent arrows. Though following code worked (ref: Adding a label to a bent arrow in TikZ)

\draw [arrow] (b8.south)++(.3,0) |- ++(0,-1.5) -| node[pos=0.225,above] {L3} (b7);

But it requires manual adjustment of position. Is there an efficient way to work around this issue?

You can use the auto and midway option for the node to place the label automatically:

\draw [arrow] (b8.south)++(.3,0) |- ++(0,-1.5) -| node[midway,auto] {L3} (b7);


EDIT: How to include L1 and L2 nodes. We replace auto by the positioning of the node we want: either left or right. There can also be a way to define the right level at which |- arrows meet. Or you can extract the y-component of b11 node using the let operation, which I have done here. You will need to use the calc library.

\documentclass[tikz]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
\begin{tikzpicture}
\tikzset{every node/.append style={inner sep=0pt,outer sep=0pt,
minimum height=1cm,minimum width=2cm,draw},
Lnode/.style={outer sep=#1,inner sep=1mm,
minimum size=0pt,draw=green,fill=green,text=red}};
%
\node[draw=red,ultra thick] (b8) at (5cm,0) {B8};
\node[minimum width=0pt,inner sep=1mm] (b9) at (2,0) {B9};
\node[draw=blue,ultra thick] (b10) at (-1cm,0) {B10};
\node (b11) at (2cm,-2cm) {B11};
% Using let operation to extract the exact coordinates for B-nodes
\draw[->] let \p1=(b11.center),\p2=(b10.center) in
(b10.south) -- (\x2,\y1) node[Lnode=1mm,midway,left]{L1} -- (b11.west);
\draw[<-] let \p1=(b11.center),\p2=(b8.center) in
(b8.south) -- (\x2,\y1) node[Lnode=1mm,midway,right]{L2} -- (b11.east);
\draw[->] (b8) -- (b9); \draw[->] (b9) -- (b10);
\end{tikzpicture}
\end{document}


Result:

• Your solution puts L3 at right place. Can L1 and L2 be done in a similar manner? Mar 4 '16 at 20:59
• Definitely, just have to include these options for those nodes. SinceB the L1, L2, L3 are different in node style to B8,B9, etc., we make a different node style for them. This time we do not use auto, but choose where to place the L-nodes: either left or right, as preferred. I have updated my answer to include L1 and L2. Mar 5 '16 at 14:41