I have a trencher that has a digging chain powered by a Danfoss Series 90 pump. I am currently unable to engage forward motion of the pump if temperatures are cold. I have to let the machine warm up for at least 30 minutes before the pump will engage. Rearward motion is also sluggish in cold temperatures, and sometimes also doesn’t want to engage. Everything works fine if temps are above 45 degrees fahrenheit. The problem started about 500 hours ago when the machine stalled out in some large fractured rock, and I had to work the motor back and forth to get the boom free. After this event, I only periodically had issues with the pump not engaging when cold. The few times this happened, you could just run the pump backwards a little and then it would run forward. The problem has now gotten worse. The Danfoss pump has a KVEB Electrical Displacement Control. My controller had the manual override lever broken off, so I replaced the controller hoping that would solve the problem, which it did not. The pump still acts the same using the manual lever. I swapped multi function valves for forward and reverse, and this did not change anything. I checked pressures at ports X1 and X2 with pump in neutral, and both pressures were exactly 160 psi. I also removed the second stage of the pump controller and cleaned all the ports and orifices, and reassembled, and this also did nothing. This is the part I changed. The second stage is still the original. Does anyone know what the problem may be? Is it the second stage of the controller, or something else inside the pump?
What is your charge pressure? What oil are you using?
What is your charge pressure both at neutral and stroked in both directions? By testing at X1 and X2 ports do you mean the M4 and M5 ports on the servo cylinder? The manuals for the 90 series are available on Danfoss's website.
LN, does your machine have a high pressure filter on that pump as well as a casedrain filter? I fitted a 90 series into a machine driving a forestry mulcher so the application is very much the same with a high pressure filter on the return line. I was told that under no circumstances was the pump to be reversed because it would backflush the filter causing any crud to go back through the system. That pump was cable controlled.
Charge pressure looked like 425 psi, assuming this is where I would check it with the filter housing. Machine has AW-32 in it. I had no issues starting the chain with this oil prior to stalling it out in the fractured rock, and I was operating it in temperatures as low as -15 Fahrenheit. View attachment 1741241411424.jpeg Charge pressure was 425 psi at neutral and didn’t seem to change when pump was stroked in reverse. Could not engage pump in forward position. Ports X1 and X2 are on the controller. Maybe these pressures are irrelevant. Is the above picture the same as what you’re talking about?
Not all pump controllers have the X1 and X2 ports for testing but all have the M4 and M5 ports on the servo cylinder. If you are not seeing a difference in pressure at X1 or X2 when actuating the pilot section then something is wrong with the pilot section or you are not getting sufficient charger oil to the pilot section. You said that there is no difference when you manually stroke the pump using the manual operator correct? I would probably verify with 2 gauges installed in either the X1-2 or M4-5 ports. The X1-2 ports are pilot oil from the pilot section and M4-5 is the servo oil from the second stage that controls the servo piston and swash plate. There should be screens and orifices at the pilot block and in the pump where the second stage bolts to the main housing. I have seen pumps become sluggish when the orifices became plugged, usually after a filter change. By the way you have pressure charge filtration which is very common on the 90 series and is the correct spot to check charge pressure. 425 is I little higher than I normally see with spec usually 390. But if case pressure is high it will bring charge and all other pressures up with it. It may be good to check case pressure especially when trying to actuate the pump. You seem to have some Danfoss documentation, do you have the service manual?
When PCP was stroked forward, X1 pressure was 410 psi and servo pressure was 0 psi (M4 or M5, don’t remember which was which). Pump would not engage. When PCP was stroked rearward, X2 pressure was 340-350 psi and servo pressure was about 1100 psi. Pump engaged and spun motor. The chain is currently removed for another repair, so there is no load on the motor. I haven’t checked case pressure yet. Like i mentioned, I did remove the second stage of the controller and removed and cleaned all orifices. I was unable to remove the pressed in screens on the pump side, so they have not been cleaned. I can have another go and try to get them out without damaging them if you think that could be the problem. I have been reading through a service manual I found online, plus a couple manuals specific to the controller, but this stuff is foreign to me, so feel free to share any ideas. There is no difference in the way the pump acts between using the electric joystick in the dash or the manual lever on the PCP, if that is what you are asking. So I’m certain it’s not an electrical problem.
I'm kinda wondering if you have an anti-cavitation valve on the motor that might be sticking. They go by different names... safety-suction, anti-cav etc. Wonder if you swapped A&B hoses, would the problem stay the same or switch.
You had 1100psi at the servo port either M4 or M5 in reverse? That should not be as that is just oil from the charge pump. Maybe you mean M1 or M2 ports.
That is possible but the charge checks are part of the multifunction valves on the 90 series so switching them should have moved the complaint to reverse not moving Of course it depends on what motor they are using. OP does your machine have a 90 series motor with planetary reduction or is it a raidal piston low speed hi torque motor like a Poclain.
What's weird is that it has to warm up, get reversed before it will allow forward travel. On second thought, even if anti-cav was the problem, he'd still build pressure in the delivery port. He reports 0 psi. Starting to wonder if the servo piston is dragging debris. My experience with those manual levers is that there's a 2-3 second delay when manually stroking but I was working with a crusher drive with -24 hoses. That could've affected the response time.
Yes, I apologize. I checked system pressure ports instead. When reversed, M5 pressure was 400 psi and would take 3-5 seconds to build pressure and engage the pump after activating the PCP. When forward was activated on the PCP, M4 only had 45-47 psi, and pump would not engage. These are the motors. The pump drives 2 of them, one on each side. View attachment 1741314848096.jpeg View attachment 1741314879900.jpeg