Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[r8f1k]

Would you mind double checking based on this diagram?

View attachment 781726

If it is on the charge pump inlet, I can’t think of any reason why it would be there. It would only lead to more pressure drop that makes it more difficult to get oil into the inlet of the charge pump.

The only place that a check valve would make sense is on the case drain. If it is on the case drain port then it wouldn't let oil flow from the tank to the pump case. I have seen that if there are case pressure spikes from another component and they are trying to isolate the pump case from those events.

If it is on the charge pump inlet line, I would remove it. If it is on the case drain line, I would make sure it is working properly and the oil can flow from the pump to the tank. It should not take much force to open it. If it does, I would be concerned about it causing high case pressure in the pump.

Here is a photo of the 1/8 gauge port that I put an elbow in to get a gauge on it.

 

[Doaaj50]

Thanks for the pictures, that helps tremendously!

I have looked at your pictures and have marked up the picture to show the case drain versus the charge pump inlet. The check valve that you showed is on the case drain, which makes more sense.

In the picture you show a gauge port. Where the threads 1/8" pipe? If so, that is a system gauge port. You can measure charge pressure there but only in neutral. In one direction that will become system pressure, in the other direction that will be slightly lower than charge pressure.

 

[r8f1k]

R8,
attached is parts break down on a Sauer Sunstrand (now Danfoss) series 40 pump. This will hopefully provide a visual aide in how these model pump is assembled. Other brands would probably be similar but none of the rotating group would interchange.

Hope this helps Vs hinders

I see you are in Northern Illinois, I am in Lake County, do you work on pumps?

 

[oldnslo]

R8
I used to work for a company that rebuilt hydraulic components but not anymore. Not even sure what repair houses are open anymore in Chicago land area. Used to be a good outfit in Elk Grove but don’t recall the name anymore.

 

[r8f1k]

If I have continued issues with this pump, can you recommend a repair kit? I would give it a try in rebuilding it myself.

 

[r8f1k]

So what you have on that machine is an old Sauer-Sundstrand 18 Series pump. The model number is 18-2081. For Sundstrand/Danfoss, anytime you see a "R" at the end of a model number, it indicates that it has been remanufactured.

The "LH" indicates that it is a Left Hand rotation pump (counter-clockwise). If the pump was sitting in front of you with its input shaft facing you, the shaft would need to rotate to the left, or counterclockwise.

Since we know that it is an 18 Series pump, we also now know that it is a closed circuit system. Oldnslo had already mentioned that based on the exploded view diagram.

Based on what you have described so far, my first thought would be to check for charge pressure. I believe oldnslo has also mentioned that in one of his posts. The problem with a direct displacement pump, is that you can force it into stroke without charge pressure. Without any charge flow, there is no oil in the circuit to send from the pump's rotating kit to the motor and thus no trencher chain movement.

The noise that you are hearing from the pump could be the charge pump running without any oil. If that has been going on for a while, then you may have an issue because those parts rely on an oil film to keep them from damage.

I would first start by making sure you have oil getting to the inlet of that pump. The inlet of that pump can be found on the diagram that is attached.

View attachment 781306

I would crack that hose fitting at the pump and see if oil is reaching the pump. If not, you will need to backtrack it to figure out where the obstruction lies. There may be a suction filter or screen that is plugged.

If you have oil at the inlet, then get a 500psi gauge and plumb it into the charge pressure gauge port and see what pressure, if any, the pump has when the engine is running. It should be at least ~100 psi. Some of the 18 series pumps ran fairly low relief settings so don't be surprised if it is at that level. It may be higher, but it shouldn't be lower than that.

In case you are not familiar with a closed circuit system, here is a system that should be similar to the one that is on your trencher.

Keep us posted on how your investigation goes. We can help direct you based on your findings.

Ok, I have oil at the pump via the inlet port, cracked the line and I have 100% flow. I connected a hydraulic pressure gauge into the 1/8 pipe gauge port and the gauge reads between 80-100psi. It bounces between the two numbers. Now I really can't run it through the paces since it its low on hydraulic fluid (still need to get more) and I am still making more replacement hoses for other accessories and I am waiting on a hydraulic cylinder to come back from the rebuilder. Is the 80-100psi good? What's next?

 

[oldnslo]

R8
Since there is charge pressure with no movement command next step would be seeing what happens to charge pressure when you attempt to turn the chain. Remember where you have the gauge will be high pressure in one direction.

 

[r8f1k]

The gauge goes up to 600 PSI, what should I be looking for when I attempt to turn the chain? A drop or a rise in pressure?

 

[laurencen]

one direction should go higher pressure,

 

[Doaaj50]

There are two scenarios that I attempted to show in my attached pictures. The first one is that your gauge is on the "low side" of the loop and stroking the pump will result in a slight decrease in charge pressure. The second is that your gauge is on the "high side" of the loop and that will result in the pressure increasing when you stroke the pump. Depending on the pressure required to turn the motor, it may exceed the 600psi rating of your gauge.