Threaded rod

Troubleshooting Challenge: Coiled-Steel Unwinder Oscillates

A shock absorber manufacturer has a standalone hydraulic system that feeds round rod stock from a coil into a machine that cuts the continuous rod to length, finishes it to the diameter needed, threads both ends, and sends finished pieces to a heat-treating furnace.

The speed and pressure on the hydraulic feed system varies with the rod diameter and the size of the coils. Operators manually feed the rod into entry unit rolls driven by the hydraulic system represented in the schematic.

The speed and preset are dictated by the rod diameter, whereas the relief valve pressure is set approximately 150 psi above the pressure required to pull (unwind) the coiled rod stock. A problem developed with the system pressure oscillating as much as 200 psi. The diameter of the control orifice—located between the shuttle valve and relief valve—was .042 in. The system worked for several years, but after the pressure oscillations began occurring, technicians replaced the main relief valve with the same brand and model number. However, the problem persisted.

Any idea as to what is causing the problem and why this would happen?

Find the Solution

Think you know the answer to this month’s problem? Submit your solution via e-mail. All correct answers submitted by October 8, 2018 will be entered into a random drawing for a $50 gift card. The winner will be notified, and his or her name will be printed in a future issue. Only one gift card will be awarded to any participant within a calendar year.

Congratulations to Kevin Breunig, Houston, whose name was chosen from those who correctly answered Troubleshooting Challenge from our last issue. A $50 gift card is in the mail to him.

Solution to Last Month’s Challenge:

Crane’s Hydraulic Malfunction Makes Operation Unsafe

The counterbalance valve operation seemed to be the problem, but technicians questionedTroubleshooting Challenge: Crane’s Hydraulic Malfunction Makes Operation Unsafe why the 2-position, 3-way solenoid valve was even in the circuit if it was never energized. When the valve’s solenoid was held shifted, the problem no longer occurred.

They just installed a new 2-position valve where the pilot line was always connected to the cap-end of the cylinder and removed the coil. Problem solved.


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