0 TO 5000 PSI GAGE
FIGURE IT OUT
BY ROBERT SHEAF, CFPAI/ AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC INDUSTRIAL TRAINING
NEW PROBLEM
Clamp and Drill Circuit Will Not Release the Part
500 - 2800 PSI 3200 PSI AIR DRILL
AIR DRILL CIRCUIT CIRCUIT CYLINDER CYLINDER
P
Any Idea what is causing the new problem?
T
3000 PSI
Solution to Previous Problem
DIRECTIONAL VALVE SEALS FAILING
B
A
A new hydraulic system was installed on an old “Clamp and Drill” machine. A PLC would shift a directional valve clamping the part and a proximity switch would then signal the PLC to advance the air operated drill. At the same time, the clamp directional valve would center, trapping the clamp pressure. When talking to the maintenance man and operator, they said that when they started up the new installation, the electrical controls engineer had the cylinder retracting when it should be extending. When they contacted the engineer, he told them to switch the cylinder hoses and everything should be OK. After switching the hoses, they found that the pressure reducing valve would only work on the rod side and allow the cap end to build to system pressure, causing damage to the clamped part. The engineer was told of the new problem, so he switched the wiring to the solenoids and also returned the hoses to their original positions. This now allowed 5 x 312 x 20 reduced pressure of the cap end and allowed the cylinder to extend when it was signaled to extend. A different problem developed. The reduced pressure on the cap end of the cylinder, after about 15 seconds, would start to slowly creep up to system pressure.
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Extruded O-rings usually are a result of pressure causing a small gap between two mounting surfaces allowing part of the O-ring to squeeze in between the surfaces. Then the O-ring gets pinched when pressure is removed, squeezing and nibbling away at the O-ring until it fails. The mounting bolts were still torqued to their proper values but were discovered to be too long. They had bottomed out in the manifold before securing the directional valve tight enough against the base plate. Replacing the mounting bolts with shorter bolts and applying the proper torque solved the problem. VISIT FLUIDPOWERJOURNAL.COM TO VIEW PREVIOUS PROBLEMS.
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MARCH/APRIL 2018
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