When I teach hydraulic troubleshooting classes, I always ask my students, “If a cylinder does not move when I shift the directional valve, is it a pressure problem or a flow problem?”.
Most of the students will say it is a flow problem. Then I ask them, “But what if I don’t have enough pressure to move the load?”
If the actuator does not move, I always think to myself, “why don’t I have enough pressure to make it move?". Something is taking my flow elsewhere at a lower pressure. Or, if it’s moving slower than it should I think, "Why don’t I have enough flow? Where is part of my flow going where it shouldn’t?”.