Troubleshooting no pressure at spool valve

[JDskidder]

I have a Midmark trencher that I have re-powered with a Kubota 4 cylinder. Just got it running but I only have pressure to drive and steering. The pump is a multi stage unit with a splitter off the final stage for steering and accessories. Since steering works fine, I’m suspecting the splitter but have limited hydraulic experience. Hoping to tap into some of the vast knowledge here. Thanks!

 

[JDskidder]

Here is a pic of the pump

 

[JDskidder]

The splitter here... top steel line goes to steering and rubber line goes to the spool valves

 

[oldnslo]

When you re-powered this unit did you remove the pump and any hoses? If yes confirm that all of the hoses are connected correctly.

In the picture of the pump it shows three hoses. One would be inlet, remaining two are the unknowns. Since you have steering the pump might have a built in priority flow control or a relief valve. I would suggest tracing these lines to see where they connect.

 

[JDskidder]

When you re-powered this unit did you remove the pump and any hoses? If yes confirm that all of the hoses are connected correctly.

In the picture of the pump it shows three hoses. One would be inlet, remaining two are the unknowns. Since you have steering the pump might have a built in priority flow control or a relief valve. I would suggest tracing these lines to see where they connect.

I did remove hoses, but they are back where I found them. The left hose on the pump is the pressure port heading directly for the splitter, the middle seems to be a return that tees into multiple lines from the power steering valve and the spool block, and the right goes to the tank. I assume this is the suction hose? I call the block a splitter because I don't really know what else to call it... one hose in and two hoses out might be a priority flow block I guess.

 

[/pine]

I have no experience with a Midmark machine...but I can tell you that if it's anything like a Ditch Witch...it is a very complex hydraulic system...The DW has both open center and closed center circuits...it has a typical (engine) powered drive train as well as a hydraulic motor through the 3 speed gear transmission...

Good luck...hope you resolve the problem and it's something simple...

 

[JDskidder]

I think Midmark was bought out a few times, but I noticed Bobcat T136 machines look almost identical to my machine. I hope it's something simple too!

 

[oldnslo]

JD,
From your description of the hose connections I suspect that pump has a relief valve in it. Since the steering is working that most likely is not the problem.

What you are calling the splitter could be a priority flow control valve. Reason for this guess is that steering and brakes typically take priority over all other functions for safety reasons.

Can you easily remove the hose going from the splitter to valves and place the end in a bucket to see if any oil come out? I would also plug the line at the valve to prevent any possibly back flow or unwanted surprises.

No flow out of the line from the splitter to the valves would point towards a problem at the splitter.

 

[JDskidder]

JD,
From your description of the hose connections I suspect that pump has a relief valve in it. Since the steering is working that most likely is not the problem.

What you are calling the splitter could be a priority flow control valve. Reason for this guess is that steering and brakes typically take priority over all other functions for safety reasons.

Can you easily remove the hose going from the splitter to valves and place the end in a bucket to see if any oil come out? I would also plug the line at the valve to prevent any possibly back flow or unwanted surprises.

No flow out of the line from the splitter to the valves would point towards a problem at the splitter.

I swapped the hoses at the output of the splitter and I lost steering, but gained plow functionality. I don't know what that block is, but it's the problem

 

[oldnslo]

is there any identifying info on the splitter valve. With luck you might something stamped on the body that will provide info on what it is. If priority valve there should be an orifice possibly in the spool and a spring. If this spool is binding it could cause the symptoms you are experiencing.