Question about my ninja warrior

[NJ104]

I was cleaning my portable machine and came time to relube my u-cup on my piston well I accidentally popped it off and now I am not sure if the u part is suppose to go towards the machine or against the piston?

 

[Bob Pruitt]

http://www.prochem.com/(X(1)S(zy1ud...c30-f7209f998791_86322420-N_Warrior200PSI.pdf

 

[Desk Jockey]

Ucup towards the valve body opposite from cap.