[pstricks] U tube

[orodrig at ualg.pt]

Dear wizards of PStricks, please enlighten me with your wisdom: I'm  
trying to create a U shaped tube with the following code:

\begin{pspicture}(-6,-6)(6,6)
\psframe[linewidth=0mm,linecolor=white,fillstyle=hlines](-2.5,0)(-2,2)
\psframe[linewidth=0mm,linecolor=white,fillstyle=hlines](2,0)(2.4,4)
\psline[linewidth=1mm,linecolor=black]{-}(-2.5,0)(-2.5,5)
\psline[linewidth=1mm,linecolor=black]{-}(2.5,0)(2.5,5)
\psline[linewidth=1mm,linecolor=black]{-}(-2,0)(-2,5)
\psline[linewidth=1mm,linecolor=black]{-}(2,0)(2,5)
\psline[linewidth=0.5mm,linecolor=black]{-}(-2.5,2)(-2,2)
\psline[linewidth=0.5mm,linecolor=black]{-}(2,4)(2.5,4)
\psline[linewidth=0.5mm,linecolor=black,linestyle=dashed,dash=5mm  
2mm]{-}(-3.5,3)(3.5,3)
\psline[linewidth=1mm,linecolor=black]{<->}(-3,2)(-3,3)
\psline[linewidth=1mm,linecolor=black]{<->}(3,3)(3,4)
\psarc[linewidth=1mm,linecolor=black,arrows=-,fillstyle=hlines](0,0){2.5}{180}{0}
\psarc[linewidth=1mm,linecolor=black,arrows=-,fillstyle=solid,fillcolor=white](0,0){2}{180}{0}
\rput{0}(-4,2.5){\scalebox{1.5}{$-\Delta z$}}
\rput{0}(4,3.5){\scalebox{1.5}{$\Delta z$}}
\end{pspicture}

It does the job, but for some weird reason either gv and acrobat  
display some "artifacts", like lines with different widths or  
non-continuous filling of the tube and arc. How can I merge all line  
and arc segments and do the filling properly? Thanks in advance  
(whatever the answer is).

Best regards

Orlando Camargo Rodríguez

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