I need to draw the picture above with tikz's code, and i would know the better way for placing the "zig-zag" lines. Also I would like to put the arrow's tip in the middle of the connection line. Someone could help me? Thanks.

This is a diffrent picture but whith the same problems:
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning,
intersections,
shapes.geometric,
decorations.pathmorphing,
decorations.pathreplacing,
decorations.shapes,
decorations.markings,
patterns,
calc,
fit,
arrows,
backgrounds,
matrix}
\begin{document}
\begin{tikzpicture}[auto]
\tikzset{deco/.style={decoration={
markings,
mark=at position #1 with {\arrow{>} }
},
postaction={decorate}},
trape/.style={trapezium,draw,shape border rotate=90,minimum width=2cm},
box/.style={rectangle,draw,minimum height=1cm,minimum width=2.5cm},
cerchi/.style={circle,draw,minimum size=1cm}
}
\matrix [row sep={1.5cm}] {
&[2cm] \node [box] (genera) {}; &[2cm] &[1cm] \\
\node [cerchi] (pompa) {}; & & \node [trape] (turbina) {}; & \node [cerchi] (ultiliz) {}; \\
& \node [cerchi] (condensa) {}; & & \\
};
\begin{scope}[>=triangle 60]
\draw [deco=0.6] (genera) -| node[pos=0.6]{2} (turbina.top right corner);
\draw [deco=0.6] (turbina.bottom left corner) |- node[above=1mm,pos=0.71]{3} (condensa);
\draw [deco=0.4] (condensa) -| node[above=1mm,pos=0.31]{4} (pompa);
\draw [deco=0.6] (pompa) |- node[below=1mm,pos=0.63]{1} (genera);
\end{scope}
\draw [->,>=latex,very thick, shorten >=4 pt,shorten <=4pt] (pompa.south)--(pompa.north);
\node [coordinate] (B) at ($ (condensa.center)!.6!(condensa.west) $) {};
\node [coordinate] (C) at ($ (condensa.center)!.6!(condensa.east) $) {};
\node [coordinate] (A) at ($ (B)+(0,-1.5cm)$) {};
\node [coordinate] (D) at ($ (C)+(0,-1.5cm)$) {};
\draw (A)--(B); \draw[decorate,decoration={zigzag,amplitude=3pt,segment length=8pt}] (B)--(C); \draw (C)--(D);
\end{tikzpicture}
\end{document}

