Hydraulic pump - positive displacement?

[AKKAMAAN]

Guy2 is totally wrong, in the fact that if the pump is turning, the fluid is being displaced and flowing.

Everything is relative...guy2 has a point that's valid, but not at the way you look at everything, on-off, 1-0, black-white etc...try to turn a gear pump 60 rpm's and move a cylinder that takes 3000psi to move....NO flow will be displaced forward, entire flow will leak back internally....a vane pump is literally useless below 1000-1500 rpms....