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\documentclass[tikz,border=10pt]{standalone}

\usetikzlibrary{shapes,arrows,positioning}

\tikzset{font=\sffamily}

\begin{document}
\begin{tikzpicture}[
    auto, 
    node distance=2cm, 
    >=triangle 45,
    block/.style = {
        draw, 
        rectangle, 
        minimum height = 3em,
        minimum width = 3em
    },
    gain/.style = {
        draw, 
        isosceles triangle, 
        minimum height = 3em,
        isosceles triangle apex angle=60
    },
    sum/.style n args = {4}{
        draw, 
        circle, 
        node distance = 2cm, 
        minimum size=5mm, 
        alias=sum
    },
    leftlabel/.style = {
        text width = 5mm,
        align=left
    }
]

\node [leftlabel] (stoff) {Stoff};
\node [right = of stoff,sum] (11) {St};
\node [right = of 11,gain, yshift=-2mm] (12) {St};
\node [right = of 12,block] (13) {St};
\node [right = of 13,sum] (14) {St};
   
\node [below = of stoff, leftlabel](energie) {Energie};
\node [right = of energie,sum] (21) {E};
\node [right = of 21,gain, yshift=-2mm] (22) {E};
\node [right = of 22,gain] (23) {E};
\node [right = of 23,block] (24) {E};
   
\node [below = of energie, leftlabel](information) {Information};
\node [right = of information,sum] (31) {I};   


\draw[->](11.east) |- ([yshift=15mm]12);
\draw[->](12) -- (13);
\draw[->](13) -- (14);

\draw[->](21.east) |- ([yshift=15mm]22);
\draw[->](22) -- (23);
\draw[->](23) -- (24);
   
\draw[->](31.east) -- ++ (1.5,0) |- ([yshift=-.8cm]22);
\draw[->](24.east) -- ++ (.5,0) -- ++ (0,1.5) -- ++ (-8.3,0) |- ([yshift=-3mm]12.west);
\end{tikzpicture}
\end{document}

\documentclass[tikz,14pt,border=10pt]{standalone}
\usetikzlibrary{shapes,arrows}

\begin{document}
\tikzset{%
    block/.style    = {draw, rectangle, minimum height = 3em,
        minimum width = 3em},
    gain/.style     = {draw, isosceles triangle, minimum height = 3em,
        isosceles triangle apex angle=60},
    sum/.style n args = {4}{draw, circle, node distance = 2cm, minimum size=5mm, alias=sum,
    },
}

    \begin{tikzpicture}[auto, node distance=2cm, >=triangle 45]

	\node [](stoff) {Stoff};
	\node [right of = stoff,sum] (11) {St};
	\node [right of = 11,gain] (12) {St};
	\node [right of = 12,block] (13) {St};
	\node [right of = 13,sum] (14) {St};
	
	\node [below of = stoff](energie) {Energie};
	\node [right of = energie,sum] (21) {E};
	\node [right of = 21,gain] (22) {E};
	\node [right of = 22,gain] (23) {E};
	\node [right of = 23,block] (24) {E};
	
	\node [below of = energie](information) {Information};
	\node [right of = information,sum] (31) {I};	


	\draw[->](11) -- node {} (12);
	\draw[->](12) -- node {} (13);
	\draw[->](13) -- node {} (14);

	\draw[->](21) -- node {} (22);
	\draw[->](22) -- node {} (23);
	\draw[->](23) -- node {} (24);
	
	\draw[->](31) -- node {} (22);
	\draw[->](24) -- node {} (12);
 
\end{tikzpicture}
\end{document}