Members with 4 wheel disc systems: Can you lock your wheels?

Looking at the parts that came out of the distribution block, it looks like it does have provisions to block flow to one side or the other.
As the shuttle moves to one end or the other, these things.....

22 6B2.jpg
......that have O rings, appear to seal off the passage. That brass barbell looking valve slides up and down but is limited by this:

22 6C.JPG