Posted on by in Figure It Out
By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training
The drum on a concrete truck rotated fine, both in clockwise and counterclockwise direction only with small loads and was limited to the projects it could be assigned to. See attached circuit.
If they exceeded about half the useable load of concrete, the drum would slow down, pulsate and stall if any more concrete was added to the mix. However, it could be rotated in the direction that discharged the load with no problem. Both cross port reliefs were screwed all the way in for their 5,000 PSI+ setting. They did notice the charge pressure was only 25 PSI higher than the hot oil shuttle relief when in the neutral position and would drop down 30 PSI when the drum was turning.
The mechanic wasn’t that good at hydraulics but felt the drop in charge pressure may be the problem. He increased the hot oil relief higher than the charge pressure and found nothing changed except the unit now would start to overheat. He reset the relief back to its original setting and did not know what to do next.
What would you do next?
See Solution
The drum on a concrete truck that rotated fine in the unloading direction but not the other under load eliminated the motor and pump as the cause. If the hot oil shuttle was stuck in one position the charge pump pressure would have increased to a high noticeable amount. The solution would be to switch the motor cross port reliefs and see if the problem moved to the other port. When the first relief was remove, they found a piece of an O-ring holding the relief poppet slightly open reducing the maximum pressure of 5,000 PSI.
Robert Sheaf has more than 45 years troubleshooting, training, and consulting in the fluid power field. Email [email protected] or visit his website at www.cfcindustrialtraining.com. Visit fluidpowerjournal.com/figure-it-out to view previous problems.