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?”.
Controlling a run-away load with meter-out flow controls normally causes intensified pressure on the rod side of the cylinder if the load is trying to extend the cylinder.
Taking the area ratio of the cylinder, (cap end area divided by the rod end donut area), multiplied by the system pressure on the cap end, will give the rod area pressure. An example would be a 3:1 area ratio, times a system pressure of 2000 PSI, resulting in 6000 PSI (PLUS what the load would add). See Fig. A.
Proper design would use a counterbalance valve with a meter-in flow control as shown in Fig. B. This will result in the rod pressure only being a...