Figure It Out

Regenerative Circuit Drops Out

By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training

»A SPECIALTY MACHINE builder was having problems getting a vertical cylinder with a regenerative circuit to lift a hinged member. When the hinged member was lowered, an attached drill would drill a hole and lift it out of the way so the work piece could move horizontally and then have another hole drilled. It looked somewhat like a band saw that would cut horizontally fed bars and angles.

When the cylinder was extended to lift the pivoting fixture up, it would extend about halfway up slowly and then pick up speed reaching the designed regen speed. You could hear oil blowing over the relief valve when it was extending slowly and stop when the regen speed was reached. Adjusting the counterbalance valves did not help.

What was the problem?

M

Solution to August 2021 problem:

Pilot Operated Directional Valve Locks Up

Pilot operated valves often have problems associated with the pilot drain and pilot pressure plugs. The rule of thumb is, if the pilot has external plumbing, there should be a solid plug installed inside the valve. No plumbing, no plugs except ones with orifices. Typically, if it is a pilot pressure problem, the valve will not shift even once. If it is a pilot drain problem, it will shift several times and then lock up. When I arrived, they could not find a schematic. When I reviewed the power unit to sketch it, I found the drain line ball valve was closed and causing the problem. To view previous problems, visit www.fluidpowerjournal.com/figure-it-out.

Robert Sheaf has more than 45 years troubleshooting, training, and consulting in the fluid power field. Email rjsheaf@cfc-solar.com or visit his website at www.cfcindustrialtraining.com.

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