We had the main lift cylinder fail on a 110' Terex telescoping manlift. The cylinder head blew off while it was parked and not operating and had not been operated for 3 weeks. We had just transported it to a jobsite and parked it. The customer said it sounded like a shot gun going off. The temperature was about 50 degs. when we parked it and about 80 degs when it blew off. The cylinder head is aluminum. Our guess is the previous owner had worked on the cyclinder and cross threaded the aluminum. Any ideas on what would cause(s) this failure besides the aluminum cross threading? Thanks in advance.
Most likely the cause is what's known as "dieseling". Some times when air gets in the cylinder past the rod seal and mixes with the oil it explodes.
Couldn't be dieseling if the machine was shut off when it happened. My money is on thermal expansion of the hydraulic oil in the confines of the cylinder. If someone just rebuilt the cylinder maybe they crossed some lines or messed up the counterbalance valve etc. I saw this same thing happen on a dump trailer, the head nut blew out of the cylinder while the trailer was being pulled down the road with nothing in the trailer box! The trailer was parked overnight in a town where the temperature got super cold,and it blew up when they pulled the trailer into warmer area. They probably powered the cylinder down all the way, so there would have been pump relief pressure in the cylinder, and with the valve closed and increasing temperature/pressure something had to relieve the pressure, so the threads failed.
i dont think it was a cross thread problem. it may have been a loose head. if its loose there will be some sort of play where it could be getting hammered back and forth as you switch functions from up to down. those cylinders have holding valves so there is always pressure in them. a bit of air would give it some acumulator like force.
Probably an inherent design defect Based on the information provided, it is plausible there was an an inherent design defect with the subject Terex Crane. I suggest you check the hydraulic schematic. If the manufacturer installed dual pilot-operated check valves in both cylinder ports, without taking into account thermal expansion, the expansion of the oil, due to heat, will increase the pressure in the cylinder by 50-PSI to 60-PSI for each 1ºF increase in temperature. Bear in mind, hydraulics is not recognized as an occupational hazard by any state or federal institution i.e. OSHA and MSHA. Accordingly, hydraulic system designers are not required to have any experience or specialized education to design hydraulic systems. As they learn, it is human nature for them to make errors. Many a cylinder has suffered an inexplicable failure due to design oversight. If indeed the "near-miss" accident was caused by an inherent design problem: as is suspected in this case, get yourself an attorney, and file a lawsuit against the manufacturer. Machinery and equipment manufacturers design and build inherently unsafe hydraulic system because they are accountable to no one, except their shareholders. Regrettably, as with General Motors, and the recent allegations regarding ignition switches, it costs money to design and build safe machines; money that could be put to better use in the acquisition of a lear jet, or a corporate yacht. Putting lives on the line in the interest of profit, which is done routinely in our country (Big Bend Mine), is capitalism at its worst: profit at any cost! The only way to put a halt to the problem, is to hit irresponsible executives and mangers where it hurts most: the wallet. "Until there is accountability, there will never be responsibility" Hydraulic safety doesn't just happen, it has to be vigorously pursued."
Possible inherent design defect Based on the information provided, it is plausible there was an an inherent design defect with the subject Terex Crane. I suggest you check the hydraulic schematic. If the manufacturer installed dual pilot-operated check valves in both cylinder ports, without taking into account thermal expansion, the expansion of the oil, due to heat, will increase the pressure in the cylinder by 50-PSI to 60-PSI for each 1ºF increase in temperature. Bear in mind, hydraulics is not recognized as an occupational hazard by any state or federal institution i.e. OSHA and MSHA. Accordingly, hydraulic system designers are not required to have any experience or specialized education to design hydraulic systems. As they learn, it is human nature for them to make errors. Many a cylinder has suffered an inexplicable failure due to design oversight. If indeed the "near-miss" accident was caused by an inherent design problem: as is suspected in this case, get yourself an attorney, and file a lawsuit against the manufacturer. Machinery and equipment manufacturers design and build inherently unsafe hydraulic system because they are accountable to no one, except their shareholders. Regrettably, as with General Motors, and the recent allegations regarding ignition switches, it costs money to design and build safe machines; money that could be put to better use in the acquisition of a lear jet, or a corporate yacht. Putting lives on the line in the interest of profit, which is done routinely in our country (Big Bend Mine), is capitalism at its worst: profit at any cost! The only way to put a halt to the problem, is to hit irresponsible executives and mangers where it hurts most: the wallet. "Until there is accountability, there will never be responsibility" Hydraulic safety doesn't just happen, it has to be vigorously pursued."