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.

 

[/pine]

Any possibility that when the work was being done that something maybe contaminated the system and has created a blockage?

Some debris broke lose or dislodged from the hoses etc??...if the disconnected hoses were left open is it possible a dirt dobber wasp blocked the end?...I have had them do that to hoses on a shelf...

 

[JDskidder]

Any possibility that when the work was being done that something maybe contaminated the system and has created a blockage?

Some debris broke lose or dislodged from the hoses etc??...if the disconnected hoses were left open is it possible a dirt dobber wasp blocked the end?...I have had them do that to hoses on a shelf...

No, I never disconnected the hoses during the time the machine sat. It had crystal clear fluid and the inside of everything looked mint when I cracked them open for the first time. I bet it's a stuck poppet like the other guy said.

 

[JDskidder]

Apparently it is a Midmark 321 from the 80s http://archive.lib.msu.edu/tic/wetrt/page/1984dec51-60.pdf

 

[Dave M7040]

Did you ever own it when it was operating properly?

You mention a re power, from what engine to the Kubota. A gas engine perhaps running at 3,600 rpm and now a diesel running much slower so nthat there is no excess flow coming out of the priority valve for steering and brakes.

Dave M7040

 

[JDskidder]

Did you ever own it when it was operating properly?

You mention a re power, from what engine to the Kubota. A gas engine perhaps running at 3,600 rpm and now a diesel running much slower so nthat there is no excess flow coming out of the priority valve for steering and brakes.

Dave M7040

No, I bought it without an engine or trencher. It had a VH4D Wisconsin so that thing was no speed demon. I think they’re rated at 2400 rpm or something like that. I put a v1505 Kubota in there and it seems to be a good match.

 

[Leejohn]

If you find out the pump is bad, I have one and well sell it. Just PM me if it turns out that way.

 

[JDskidder]

Update on this problem: The good news is that something broke free in the valve block in question during some testing and I got steering and plow function. The bad news is that just when I turned the steering to the max it hit the relief pressure and I got a small shower of fluid out of the rusted top cap. There is a piece of o-ring that's sticking out like a hernia! I am going to see if I can get away with a Prince RD-208-8 http://www.princehyd.com/mobileserv...ature?fileKey=catalogSect-ModelRD200PD0-30GPM I got a good deal on it and the original Cessna part is cast from unobtainum. Does anyone here know what the difference on the system would be in case the original valve was a priority flow control valve? It did seem to act like one from what I have read. With RPMS low I had full steering, but very slow plow moves. I had to bump up the throttle to get enough flow to move the plow at a reasonable rate.