I acquired a 2005 Bobcat 430 last fall and noticed right away that the boom hydraulic would occasionally cut out when lifting. I also had an issue with the right track hanging up so in the process of sorting that I have checked and adjusted the pilot pressure so it's within spec. I've installed a tee on the pilot and boom circuit with pressure gauges that I can monitor and have found that the boom starts to 'hop' up when the pilot pressure reaches about 375psi and cuts out near 390psi. The boom circuit pressure never appears to climb above 3200psi unless I have a full load in the bucket and it bounces but never gets close to the 3915psi max. When I first start the machine the boom circuit seems smooth a functional but as the hydraulics come up to temperature the boom circuit begins to misbehave. Under 2050rpms engine speed everything seems functional and smooth but once I exceed 2050rpms the pilot pressure on full joystick pushes into the range that causes the boom hydraulic to start cutting out or bouncing up. It also seems that if I am booming up and swinging the slew at the same time the boom doesn't appear to cut out. I say "seems" because I can't be absolutely certain that I'm not imagining that the issue resolves with the combination action. I'm running Deere pattern controls so boom and swing are both on the Left joystick. I ordered a 3915psi pressure relief valve from Bobcat last week and installed it this morning but this didn't resolve the issue. Any thoughts?
Good day Any noise from the pump coupling? Kind regards Uffex
I would just like to point out that unless you have the boom cylinders stalled there is no way that the pressure in the circuit will reach the 3915psi of the relief valve setting. The whole idea of the relief valve is to "relieve" pressure in a system which cannot physically move in order to prevent something mechanical breaking.
I don't notice any rattling or knocking from any hydraulic components. I do get an occasional whoosh sound like a return to tank valve releasing pressure but it doesn't coincide with any hydraulic malfunction.
Yes, I wouldn't expect the system to exceed the pressure relief valve maximum except if the boom is subject to severe overload. My presumption after running the multiple field tests was that the valve was defective and was popping prematurely but with a new pressure relief valve supplied directly by Bobcat my boom circuit still seems to be bypassing even though the pilot pressure is steady and the boom pressure is never exceeds, nor approaches the factory preset value of 3915psi. Looking for alternate theories that might explain my symptoms.
Good day It appears to me that the issue is connected to the pilot pressure, from what information I have the servo pump provides power for the fan drive in addition to providing pilot system, the pressure at the relief valve should remain in the 435 p.s.i. (30 bar) range with full lever movement 400 p.s.i. is ok but less must be made good to move on troubleshooting. I recommend you install a gauge to the boom raise pilot line and monitor what happens when the trouble occurs. Note the pressure from the pump is fixed at 435 p.s.i. Servo pressure, the pressure from the R.C.V is variable between 0-435 p.s.i. Pilot pressure according to lever movement. Kind regards Uffex
I do have a tee with a test gauge installed on the pilot pressure input at the valve block. My pilot pressure from the manifold was checked and adjusted when I was diagnosing a slow travel motor a while back so I have confirmed it is within spec. What I found was that the pilot pressure from the Left/back joystick movement (boom raise action) came up properly and that the boom would raise accordingly until the pilot pressure reached around 370 to 375 psi then the boom would begin to 'hop' or cut out entirely if above that 375 pilot pressure. The pilot pressure at full stick tops right at or just below 400psi and is steady. As a further check I switched my control configuration to move the boom to the right hand control and found that the issue stayed consistent and identical to how it behaved in my normal configuration. I have video of the gauges during operation but I can't seem to find a format that the forum host can accommodate. I appreciate the feedback so far.
Upload to YouTube then link to a post here.
Good day Walter You explain you have switched the boom raise pilot line, have you also switched the boom lower pilot line? Kind regards Uffex