Pneumatic Linetype

Add this string to your line type file, or better yet, copy the existing line file and make a new one with this and others in place:
*PNEUMATIC_LINE,Pneumatic-Line -------- // -------- // -------- // -- A,2.5,-.3,["//",Standard,S=1,R=0.0,X=-0.1,Y=-.05],-.4
Play around with the second line settings such as the 2.5, -.3 and -0.4 to adjust the fit of the symbol, etc.