The purpose of counterbalance is to keep the load under control while (in this example) the cylinder is extending and the load is descending. This application uses an external piloted counterbalance valve. Depending on the application, external piloted counterbalance could be appropriate. The directional control was properly selected using a float center spool. It closes in 30 thousandths of a second. This is typical for a standard (non-proportional) directional control valves.

The static load pressure is only 1,442 psi and the cylinder is rated at 5,000 psi. However, from the calculations shown the pressure during deceleration rises to almost 9,000 psi. This pressure will, at the very least stress the rod seal and will cause premature failures. And, you won’t see this on a pressure gauge. Gauges are typically too slow responding. WARNING: This could also represent an extreme safety problem.

What must be done to fix this problem? The closing time of the directional control valve spool must somehow be increased. This could be done with a simple proportional directional control valve or by replacing the existing standard directional control with a ‘slow shift’ valve of some sort. If the directional control valve is a pilot operated type with meter-out pilot choking increasing the spool closing time could work. If a proportional valve is used, we must apply proper sizing techniques and apply ramp time to the spool. The advantage of a proportional directional control valve is elimination of the manual flow control valves.

If the directional valve closing time is increased to 100 milliseconds through one of the described methods the pressure during this increased deceleration time is reduced to approximately 3,700 psi and is well within the pressure range of cylinder.

(The purpose of this example is to show how deceleration time can directly affect peak pressure on the cylinder’s rod side)