to control the flow of fluid between the two chambers when shock absorber 26 extends in length an additional volume of fluid is needed in lower working chamber 46 due to the u201c rod volume u201d concept thus fluid will flow from reservoir chamber 54 to lower working chamber 46 through base valve assembly 40 when shock absorber 26 compresses in length an excess of fluid must be removed from lower working chamber 46 due to the u201c rod volume u201d concept thus fluid will flow from lower working chamber 46 to reservoir chamber 54 through base valve assembly 40 referring now to fig3 piston assembly 32 comprises a piston body 60 a compression valve assembly 62 and a rebound assembly 64 compression valve assembly 62 is assembled against a shoulder 66 on piston rod 34 piston body 60 is assembled against compression valve assembly 62 and rebound valve assembly 64 is assembled against piston body 60 a nut 68 secures these components to piston rod 34 piston body 60 defines a plurality of compression passages 70 and a plurality of rebound passages 72 seal 48 includes a plurality of ribs 74 which mate with a plurality of annular grooves 76 to permit sliding movement of piston assembly 32 compression valve assembly 62 comprises a retainer 78 a valve disc 80 and a spring 82 retainer 78 abuts shoulder 66 on one end and piston body 60 on the other end valve disc 80 abuts piston body 60 and closes compression passages 70 while leaving rebound passages 72 open spring 82 is disposed between retainer 78 and valve disc 80 to bias valve disc 80 against piston body 60 during a compression stroke fluid in lower working chamber 46 is pressurized causing fluid.