I'm not sure that the release valve is involved in this failure, because I'm not yet convinced that type of rod fracture can be caused by the tractor's hydraulic system pressure - with or without the release valve working.
What other forces could brake this in the middle of swing with bucket of gravel on flat ground?
The relief valve only protects against over-pressure from the tractor's hydraulic pump .... and depending on the design, sometimes from hydraulic shock loads. The relief valve could be working fine and there still be other purely mechanical forces large enough to break the rod.
They other forces are probably more important now that the rod has broken because they are mechanical functions of the geometry of the backhoe. That is dealer and designer stuff.
One set of forces would happen if the rubber swing stops are not positioned right. You can see those rubber cushions in several of the photos. Those might be poorly located and allow the swing motion to stop by smashing into something solid instead of the cushion. That could start a fracture in the rod. Once a fracture starts, it doesn't take much repeated stress to make it grow. Just repetitions and time.
Or if the cylinder rods were bottoming out internally before the swing stops. That could do it.
Also, something less obvious could be putting side force on the cylinder rod. For example, the open end of the rod has to rotate around a pin. Does it have enough rotation or does something stop the rotation and cause the rod pin end to bind before the end of the swing? I've made that mistake myself.
That rod failure is a mechanical issue with the backhoe. Either the stops are poorly located or the geometry sucks.
The backhoe should mechanically stop swinging before the cylinder bottoms. If it doesn’t, you bend rods or pop pistons off the rod. It may be a design issue or a manufacturing issue, or both.
The cylinders should not be side loaded by the backhoe while swinging. If they are, you fail things.
Your dealer needs to be heavily involved. If this is inherent design issues, you may need to ask for a return of the backhoe.
All good ideas.
Dude also asked "What other forces could break this in the middle of a swing with a bucket of gravel.....?"
Well, there are also hydraulic forces that happen due to sudden changes in motion - especially when you close the valve and the swing suddenly stops. Having a load of gravel in the bucket makes those forces larger. Think of water hammer in house plumbing. Hydraulic forces from abrupt changes in motion are smaller than the mechanical ones of slamming against a stop - but still large. If the cylinder rod already had a crack growing from some other cause, those forces could be enough to cause it to come apart in the middle of a swing.
Or maybe you were just unlucky and got a rod with a defect. It happens, but that might be the best news of all. My guess is that the dealer is still involved in any of thes things.
Luck,
rScotty
