By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training.
Back in 2016, I wrote up a problem on a machine that made sand cores. See the original circuit attached. Everything seemed to be the same other than they had omitted the other circuits that ran a couple small cylinders that were not used any more.
Lately, they started having overheating problems that needed to be corrected. The unit was located on a 300-gal reservoir, and they did not have this problem with overheating until they removed the 2-small cylinders that were plumbed after the check located near the accumulator.
Maintenance felt that the problem was with the main pump relief and solenoid valve #1 so they replaced both valves. This did not fix the problem. Unfortunately, they were not familiar with the Core Squeeze circuit thinking it could be the problem and asked for help.
In all the years I have been teaching, it still amazes me that most technicians don’t understand the function of solenoid valve #1’s function. The 1000 PSI main relief valve is of the pilot operated design and if the “Vent or X “port is directed back to tank, the relief opens and the only pressure attainable is caused by the 25 to 50 PSI bias spring. This circuit relies on the pressure switch signal to load or unload the main relief by controlling the Solenoid valve. If the Pressure switch is set too high, the relief never releases, causing high pressure oil to flow to tank creating excessive heat. Adjusting the pressure switch lower solved the problem.
Robert Sheaf has more than 45 years troubleshooting, training, and consulting in the fluid power field. Email firstname.lastname@example.org or visit his website at www.cfcindustrialtraining.com. Visit fluidpowerjournal.com/figure-it-out to view previous problems.