Click Motion from the Setup tab:
Hide the pipe wall.
Select the poppet.
To open the Motion quick edit dialog, do ONE of the following:
On the Motion task dialog, set the Type = Linear
Direction: Click the ... button, and select X
Initial Position: Key in -5 (do NOT click enter)
Check Flow Driven
Minimum Bound: Key in 0 (do NOT click enter)
Maximum Bound: Key in 12 (do NOT click enter)
Click Edit to open the Motion Editor
Click the Resistive force button.
Variation Method = Spring.
Engagement displacement = 0 mm
Compression displacement = 15 mm
Engagement force = 2.2 Newtons
Compression force = 44.5 Newtons
Click Apply.
Click OK.
Click Apply on the Motion quick edit dialog.
For more about assigning motion
For more about defining flow-driven motion