Create loop arrow in TikZ
As I said in comment, with precise number
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node at (0,0) (Operations) {Operations};
\draw [->] (Operations.south)arc(-160:160:1);
\end{tikzpicture}
\end{document}
Another approach
\draw[->,shorten <=5pt,shorten >=5pt](Operations.center)arc(-180:180:1);
Third approach
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node at (0,3) (Input) {Input};
\node at (0,1.5) (Operations) {Operations};
\node at (0,0) (Output) {Output};
\draw [->] (Input) -- (Operations);
\draw [->] (Operations) -- (Output);
\draw[->](Operations.south)arc(-180:0:1)coordinate(X)
(Operations.north)+(2,0)--(X)
(Operations.north)+(2,0)arc(0:180:1);
\end{tikzpicture}
\end{document}
Here a very grob solution by adding a third node \node at (1,0) (here) {};
and modifiyng the arrow's size by looseness
.
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node at (0,0) (Operations) {Operations};
\node at (1,0) (here) {};
\draw [->] (Operations) to[out=-80, in=-90,looseness=2] (here) to[out=90,in=80,looseness=2] (Operations);
\end{tikzpicture}
\end{document}