Hi Alex,
I downloaded your file, but you only put the .wbpj file in there. That file is useless without the _files folder of the same name. The proper way to share files is to use File > Archive and create a .wpbz file which is an archive of that file and folder in a single file, like a zip archive file.
I started with my Air solid file that is attached.
1) Create a Component called Inlet
Click on Sketch and click on the top face of the air column. Draw a circle.
Type P or click the Pull tool. Pull the surface up to the length you want for the inlet.
Click on the Workbench tab, click on the Share tool, type 0.01 into the Coincidence Tolerance box.
Repeat for the outlet end.
Good luck!
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