Hi everyone, I have a hydraulic issue with my 988K TWX01834. When I tilt back, I can’t raise—it’s as if all the flow is being used by the tilt. The pilot pressure is good, around 530 psi ± ~50, and on the implement valve at the pilot pressure port for both tilt and raise, the pressure remains the same for both at 515 psi. I swapped the two PWMs and their cartridges, but there was no change—the tilt is still prioritized. If I release the tilt-back, I can raise, and if I tilt back, the boom starts to raise a little without being commanded. Thanks
That's normal and by design. That's not normal and seems to contradict your previous statement. What's the history of the problem?
The operator told me that He can't tilt and raise at the same time. I got another 988, but this time H, and when I tilt, I can only raise once the tilt is fully backrack. On my K, it only raises if I release the tilt and it makes a bang in boom cylinder like if the spool stuck but move freely, and I've noticed that if I hold the tilt backrack all the way backrack, the boom starts to rise—the more I hold the tilt backrack, the higher it rises.
Sounds like a loose piston.
First, the 988H and 988K are pretty much the same as far as the implement control valves are concerned. The tilt spool has priority and as long as the tilt spool is fully actuated, there should be minimal flow getting to the lift spool. So if you stall the tilt in rackback the bucket lifts without moving the lever in the cab, correct? That's strange behaviour. Although I can't see how it could have any effect, I would start by carrying out the lift and tilt lever sensors and solenoid valves calibrations. Maybe some internal leakage between the solenoid valves?
Yes, that's correct—if you tilt the backrack, the boom raises slightly. The calibration was performed while I was observing the levers with ET 0 V, so it's possibly due to an internal leak. As for the tilt priority, after checking the hydraulic diagrams, you're absolutely right, but the operator swore to me that wasn't the case. Anyway, thanks for confirming.
Do the machines have ride control? I've seen it on both 988 and 980 machines with ride control.
Yes, it’s equipped with Ride Control. I’ve disabled it via the display, but if I tilt backrack and hold the lever all the way down, the boom still lifts slowly, and if I activate the lever to raise it, it gives a violent jolt. Regarding the issue the operator mentioned to me at the beginning, it’s unable to tilt and raise at the same time, but as mentioned above, tilt would take priority. After looking at the diagrams, it’s clear that the valve is a center-open type—is that correct?
As always, what's the serial number? There are some minor changes.
Yes. Uncommonly for a piston pump arrangement, the valve is kind of open centre. The last spool in line - lift - is open but with an internal restriction to give some back-pressure.
Do you have a schematic of the hydraulic system with the ride control? You can disable the electronics for the ride control but you can't isolate the piping and valves completely.
With a machine Serial Number I can probably come up with one.