Changing Cylinder Size Causes A Drifting Problem
A customer of ours bought a machine that had a damaged cylinder that needed to be replaced. The rod was bent, and they ordered a replacement cylinder with a larger diameter rod thinking it would eliminate the original problem.
The machine was put into production and worked well with one exception. Each time they stopped the cycle for more than 15 seconds, the cylinder started to drift out causing a potential safety problem. The cylinder supplier shipped them a replacement cylinder, but the problem persisted. The circuit was confirmed to be correct and matched the machine hydraulic set-up.
Any idea what could be causing the problem?
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By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training
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The main DCV is the issue. Because the valve neutral position is all ports blocked, the pump and accumulator pressure migrates from P to and A and B at equal pressure. Because there is a difference in areas on the cylinder, when you have 2000psi on the bore and rod side, the cylinder will creep extending. Should change valve configuration to P blocked, A and B to Tank, with a dual PO check to stop cylinder creep.