My autocad 2011 3d modeling file too big. Its 115MB

[Anonymous]

My AutoCAD 2011 created 3d modeling DWG file too big. its 115MB and hard to edit and make changes. So laggy. I also have AutoCAD 2018 student version.I opened it with AutoCAD 2018 and it takes 45 minutes. Also, I used purge command, DXF trick, Audit, Wblock, All of them none work.

I don't understand. How should I let this big size down?  I attached my file pdf version for you just average size calculate.

[ennujozlagam]

@Anonymous hello, have you try to copy and paste into a new file and see if helps. thanks

[Anonymous]

thank you for the reply. I tried. no luck. I also figured out one thing. In my drawing have 6 valves. I separated only one valve and deleted other things and saved. Size about 30MB. Next, I used UNION command and combined parts into one solid and saved then checked file size was only 80KB. 

I really don't understand. I am also using AutoCAD only 3 months and don't know much more.