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\documentclass{article}
\usepackage{tikz}
\newlength\rc% the circle's radius
\setlength\rc{5mm}
\begin{document}
\begin{tikzpicture}[>=latex]
\setlength\rc{3cm}%
% the circle:
\draw (0,0) circle(\rc);
% equilateral triangle with its tips touching the circle:
\draw[help lines, green] (0,\rc)% from the circle's topmost point
-- +(240:1.732\rc)% 30° west of south
-- +(300:1.732\rc)% 30° east of south
-- cycle;% 1.732: sqrt(3) * r
% the circle's radius from the triangle's lower left tip:
\draw[help lines, green!70!black] (0,\rc) +(240:1.732\rc) -- (0,0) node[midway, above=-2pt, sloped]{$r$};
% the circle's centre point cuts the equilateral triangle's height 2:1
% 2 parts for the outer circle's radius (the one connecting the tips),
% 1 part for the inner circle's radius (the one not shown touching the triangle's lines)
\draw[help lines, green!70!black] (0,0) -- (0,-0.5\rc) node[midway, right=-2pt]{$\frac{r}{2}$};
\draw[help lines, green!90!black] (0,0) -- (0,\rc) node[midway, right=-2pt]{$r$};
% To open up the `V' (which is upside down here), I suggest adding another length of r/2:
\draw[help lines, cyan] (0,\rc) -- (0,1.5\rc) node[midway, right=-2pt]{$\frac{r}{2}$};
% Using the topmost point as the topmost tip of the V's (upside-down) triangle
\draw[cyan] (0,1.5\rc) -- ++(246.59:2.18\rc)
node[near start, above, sloped] {$\frac{\sqrt{19}}{2} r$};
\draw[cyan] (0,1.5\rc) -- +(293.41:2.18\rc);
% and using the topmost tip of the equilateral triangle as center for the arc---which gives the V a bell-like appearance---in the bottom:
\draw[red] (0,\rc) +(240:1.732\rc) arc(240:300:1.732\rc);
\draw[help lines, red, ->] (0,\rc) -- +(255:1.732\rc); % the arc's radius
\end{tikzpicture}
\bigskip
Erasing all the help lines, nodes, and everything that's outside the circle:\par
\begin{tikzpicture}
% diaphragm pump:
\draw (0,0) circle(\rc);
\begin{scope}
\clip (0,0) circle(\rc);% clip everything outside the circle
\draw (0,1.5\rc) -- ++(246.59:2.18\rc)
arc(240:300:1.732\rc)
(0,1.5\rc) -- +(293.41:2.18\rc);
\end{scope}
%turbomolecular pump:
\draw (3,0) circle(\rc);
\begin{scope}
\clip (3,0) circle(\rc);
\draw (3,1.5\rc) -- ++(246.59:2.18\rc)
(3,1.5\rc) -- +(293.41:2.18\rc);
% to match the diaphragm pump's arc (bottom of the outer, hmm, turbo ring should be the same heigth
% as the bottom of the diaphragm pump arc's bottom), I just used the same distance between arc's
% bottom and the symbol's outer circle (2r - 1.732r = 0.268r) as distance between the two circles forming
% the `turbo ring', with the same value being the radius of the inner circle of this ring, so the center
% of the two circles forming the ring should be at 3*0.268r -1r = -0.196r, with a radius of 0.268r
% for the inner ring's circle, and twice that for the outer one:
\draw (3,-0.196\rc) circle(0.268\rc) circle(0.536\rc);
\end{scope}
\end{tikzpicture}
\end{document}
