Troubleshooting Challenge: Repeated O-Ring Failures on a Cross-Port Relief

Feb. 3, 2020
Try your hand at solving this month's head-scratcher.

The schematic below shows a hydraulic motor system that controls the motion of a giant ladle used to move molten steel. When the directional valve is de-energized, the cross-port pilot operated relief slows the ladle as it is lowered and is controlled remotely by a technician.

The mill had problems with the O-ring between the incoming pressure of the cross-port relief and its outlet. The Buna-N O-ring kept failing. A maintenance crew replaced it with a Viton O-ring. They also changed the back-up ring that went between the O-ring and the outlet. It seemed to last somewhat longer than the Buna ring, but it too kept failing. The O-ring also would erode in one area and fail.

Maintenance checked the bore measurements of the steel block the relief screwed into and found they were well within given tolerances. So why is the O-ring repeatedly failing?

What’s the Problem?

Think you know the answer to this month’s troubleshooting problem? Then email it to [email protected] (put “Feb Troubleshooting” in the Subject line). All correct answers received by Feb. 20, 2020 will be entered in a random drawing. The winner will be mentioned in a future column.

Solution to last month’s problem:

Hose Keeps Failing on a Large 100-Ton Press

When the crane cylinder was being tested for two hours, they needed to keep the ambient temperature somewhat consistent. Oil expands approximately .005% per 10ᴼF change. This would cause the 10-in. bore cylinder to extend just short of ½-in. A 20ᴼF change would cause it to extend almost 1 in. The reverse is true; the volume can decrease if the rain caused the temperature drop. The sun shining on a cylinder can cause the rod to extend.

Robert J. Sheaf, Jr. is founder and president of CFC Industrial Training, a division of CFC Solar, which provides technical training, consulting and field services to any industry using fluid power technology. Visit for more information.

About the Author

Robert Sheaf | President

Robert J. Sheaf Jr., is the founder and president of CFC Insustrial Training, formerly Certified Fluid Consultants, part of CFC-Solar Inc. CFC-Solar provides technical training, consulting, and field services to any industry using fluid power technology. 

Continue Reading

Handbook Simplifies Advanced Aspects of Mobile Hydraulic Controls

May 10, 2017
Author Brendan Casey lays out his hydraulics know-how that he acquired over 27 years in a simple handbook made for people that want to improve their skills in troubleshooting ...

The Impacts of Electrification on Fluid Power Systems

May 15, 2023
Electrification presents challenges as well as opportunities to re-evaluate and improve upon the design of hydraulics and pneumatics.

Sponsored Recommendations


May 15, 2024
Production equipment is expensive and needs to be protected against input abnormalities such as voltage, current, frequency, and phase to stay online and in operation for the ...

All-In-One DC-UPS Power Solutions

March 13, 2024
Introducing the All-In-One DC-UPS, a versatile solution combining multiple functionalities in a single device. Serving as a power supply, battery charger, battery care module,...

Motor Disconnect Switches

March 13, 2024
With experienced Product Engineers and Customer Service personnel, Altech provides solutions to your most pressing application challenges. All with one thought in mind - to ensure...

DC Power Solutions: Streamlined Power Supplies for Every Need

March 13, 2024
CBI All In One UPS Power Solutions combine the requirements for several applications in just one device which can be used as power supply unit, battery charger, battery care module...