What is in this article?:
- Fluid power safety in the workplace, part 3
- A common occurrence?
This is part 3 in a series on the importance of following good safety protocol in fluid power system maintenance and design. It highlights real-life examples of the dangers and injuries that can occur and provides advice on preventing them. Find part 1 here; part 2 here; part 4 here; part 5 here; and part 6 here.
Scenario: Mike, a maintenance supervisor and Walt, a maintenance mechanic, were severely injured as a result of an accident they caused while disassembling a large hydraulic cylinder. The accident occurred while they were trying to remove the rod/gland assembly from the cylinder. In their attempt to remove the assembly, they first pressurized the cylinder with approximately 100 psi compressed air with the objective of pushing the gland out. The attempt failed.
Then they figured that if —in addition to applying force with compressed air —they heated the cylinder barrel in the vicinity of the gland assembly, the cylinder tube would expand, and possibly release its grip on the gland assembly.
They used an acetylene torch with a rosebud tip to apply heat to the surface of the cylinder tube. Within minutes, the gland assembly unexpectedly blew out with a deafening explosion that was heard throughout the complex, Figure 1.
The ambient air collected the residual oil in the cylinder as it rapidly de-compressed. The air/oil mixture ignited into a fiery inferno when it contacted the torch’s open flame. Both men were knocked to the ground by the forces of the giant explosion. They were both covered in hydraulic oil as it sprayed out of the open end of the cylinder tube —and both were quickly engulfed in flames.
A passer-by grabbed a nearby fire extinguisher and doused the flames. The heavy gland assembly had ripped Mike’s leg off as the compressed air blasted it out of the cylinder. He also suffered extensive burns. Walt suffered extensive burns and a broken leg.
Events that led to the accident
Walt was carrying out a routine service on a large hydraulic cylinder that included an inspection of the internal wear rings. He noted that there was some external leakage from the rod/gland seals. The cylinder design was typical of those found in mobile hydraulic applications. This design usually has a gland assembly recessed inside the open end of the rod end cap. The assembly is secured with a metal retaining ring that fits into a groove machined around the ID of the cylinder tube, Figure 2.
After removing the retaining ring, he tried in vain to extricate the rod/gland assembly manually. All indications were that it was seized. In his next attempt, he tried to pull the rod/gland out by attaching it, via a cable, to a forklift truck. This also failed to move the gland assembly.
Walt discussed the problem with Mike, his maintenance supervisor, and together they decided to try to push the stubborn gland assembly out with compressed air, Figure. 3. They went so far as to calculate the force that 100 psi would generate against the gland area.
They installed a quick-disconnect fitting to the port at the cap of the cylinder. Then, they connected the air-supply hose from the compressor to the cylinder port, and pressurized the cylinder with the air. They observed the pressure on the air compressor’s pressure gage. The compressed air, and resultant force, failed to push the gland assembly out as they had planned.
After further discussion, Walt and Mike decided that the cylinder tube’s grasp on the gland assembly might be relinquished by using heat to expand the cylinder tube in the vicinity of the gland, Figure 4. Using an acetylene torch with a special tip for heating. Mike applied heat to the cylinder tube, distributing the heat uniformly around the outside diameter of the tube. After approximately three to five minutes, the explosion occurred.