EX120-2 system base pressure too low

[Jason Klassen]

More weird things found with the thermal camera today! My brother was watching the main control valve while I pulled one of the track levers. The throttle was in L, I pulled one track lever and had to wait a couple of seconds for the track to try and turn. It tried and then did not move. The engine did load up so it was trying. I held the lever there with the track not moving and the engine loaded. While watching the mcv the hard lines for the bucket and arm variable pressure compensators started to warm up. On the camera you could watch them become more and more yellow while the track lever was held and the track was not moving. After letting the track lever go the lines could be observed cooling down. We waited until they reached the same temperature as the other hard lines which did not take very long. Then we did it again, held the track lever, track stalled, and the lines for the bucket and arm vpcv warmed up.

The bucket was off the ground and the control joysticks were neutral, only the one track lever was being moved. I don't know why compensation for the bucket and the arm would be required? Maybe I should try unplugging the two proportional solenoids that feed those lines?

 

[Jason Klassen]

I unplugged the proportional solenoids for the bucket and arm, and then held the track lever and it stalled just like yesterday. While holding the track lever and watching those two hard lines with the thermal camera I could see them heating up just like before.

So unplugging the solenoids apparently did nothing, there is still oil flowing to those variable pressure compensators even though they should not be active when only the track function is being activated.

Guess I am going to have to pull that little solenoid bank apart and have a little looksee!

Does anybody have a diagram or somethings that shows how the pilot oil is supposed to flow through this solenoid bank?

This is what I'm talking about:

 

[Jason Klassen]

Did a little more testing today. I was looing around with the thermal camera and noticed the swing parking solenoid was warmer than the other solenoids at idle. According to the manual the swing parking solenoid should only activate when the swing pressure switch or arm in pressure switch is tripped. Then the solenoid sends full pilot pressure to the swing parking brake, pushing on the spring and releasing the brake so the machine can swing. This means the swing parking brake is normally "on" without pressure from the solenoid, so the solenoid should have been off while the machine was idling with no functions being used.

I then unplugged the harness connector to see of the swing parking brake would apply. Turned the machine on and tried to swing and wouldn't you know it, it swung just fine. So even with the solenoid unplugged pilot pressure must still be getting to the swing parking brake. I teed in a gauge between the solenoid and the swing motor and got about 690 psi. Pilot pressure is 720 psi at idle. So I have almost full pilot pressure leaking from the solenoid bank to the swing parking brake with the solenoid unplugged.

Next I noticed the line for the travel speed control was getting warm while the machine was still stationary and the travel speed was set to turtle mode. The travel speed solenoid is only supposed to send pilot pressure to the travel motors when fast speed is activated. With slow and medium the pressure in the travel speed line should only be 14-71 psi. I put my gauge back into the travel speed line and got 200 psi. I then unplugged the solenoid and got 150 psi. Previously while engaging fast travel speed I had recorded only 500 psi when it should have been 700+ psi. Maybe I can't get the full 700+ psi when it tries to shift to fast mode because it seems to be leaking pilot pressure even with the solenoid unplugged.

I also read in the manual that it only takes 183 psi to start the change to fast travel speed. This could be the cause of my week travel issues. Even in turtle mode there is pressure leaking into the travel speed changing line and possibly partially shifting the motors into fast travel mode.

I need to get a more accurate gauge for these lower pressures. My lowest gauge goes from 0-3500 psi but the needle rest is the 100 psi line so its kinda hard to tell. I will have to find a 0-1000 psi gauge.

 

[Jason Klassen]

Alright, I had the solenoid block apart and the manual was not very clear on the swing parking operation. In the previous post I described it backwards.

Turns out the swing parking solenoid works in reverse compared to the rest of the solenoids, which are for proportional control. The swing parking is simply on/off. In its resting state the swing parking solenoid allows oil to flow while the proportional solenoids in their resting state do not allow oil to flow. This is why the swing parking solenoid is "on" while the machine is idling. It is blocking the oil flow so that the parking brake is engaged. When you want to swing the machine the computer turns off the solenoid and oil flows to the swing parking brake and releases it. I think they designed it like this so that the solenoid would not have to be "on" the whole time the machine is in operation.

After pulling all the parts out I noticed some were missing according to the parts diagram. A small spacer disk and spring washer. The spacer disk was missing from the travel speed control solenoid. I made new one and I don't think there is anymore pressure leaking out causing it to change travel speed without any buttons being pushed.

I put compressed air into one of the pressure ports and activated each solenoid individually with a battery. Air would flow only when the solenoid was activated so I believe they are working fine now.

Still waiting on my 0-1000 psi pressure gauge so I can know for sure.

 

[Jason Klassen]

Doing some more testing while waiting for my pressure gauge. I believe the leaking solenoids are fixed so it is now longer trying to change into high speed travel without my say so.

Problem is the tracks are sometime really slow to respond to input. When I first fire it up I can move the travel control levers and it responds basically right away. If I try to do some digging and swinging and then go to move the tracks I sometime have to wait for 10, 15, or 20 seconds for a response.

I hooked a gauge to the pilot cap and there is pressure there right when I pull the lever. The pressure doesn't drop while I'm waiting. Eventually the sound of the engine changes and the tracks pick up speed slowly. Like it finally realized there is load on the system and a response from the pump is required.

I have tried moving another function while waiting and it sometimes causes the tracks to start moving but not all the time.

I know this sounds like a load sense issue with the shuttle valves but I did clean those when the mcv was out. They weren't dirty then so I kinda doubt they are now.

It also still has:
- low system pressure when everything is in neutral
- combined operation for boom and arm does not work
- while tracking the boom will not raise at all.
- swing is really weak
- arm out is really weak
- tracking is better since its not going into high speed anymore but response can be delayed and when turning it will sometimes just stop like a got too difficult for it.

I am waiting for the gauge and a new palm pilot to put drzx on. The one I have seems to connect 1% of the time lol!

 

[mg2361]

I hooked a gauge to the pilot cap and there is pressure there right when I pull the lever. The pressure doesn't drop while I'm waiting.

When you get your palm pilot, it will be interesting to see how fast the Dp sensor is reacting.

 

[Jason Klassen]

When you get your palm pilot, it will be interesting to see how fast the Dp sensor is reacting.

Yes, it will! The weird thing is that all the other functions seem to respond right away. I am still a little suspicious of the Dp sensor though.

Have you ever heard of main control valves developing cracks internally? I had somebody suggest this to me as a possible cause for the low pressure when everything is in neutral.

The other thing they suggested doing is capping every line that leaves the mcv and then opening one circuit at a time to see if fluid is leaking into the circuit.

 

[mg2361]

Have you ever heard of main control valves developing cracks internally?

Absolutely. Just haven't seen it in a Hitachi control valve....yet.

 

[Jason Klassen]

Absolutely. Just haven't seen it in a Hitachi control valve....yet.

Hmmm, well I just might be your lucky customer lol! Is there a way to diagnose an internally cracked mcv? I wish I knew what to look for when I had it out before!

 

[John C.]

I've seen in Dash 3 Komatsu excavators. The only way I've found them is because pressures were lost when they shouldn't have been or something else moved when it should have. One machine had split in between the valve halves. Two machines had a break in the straight travel valve circuit. We were never sure of what happened, only that the problem went away when we changed the problem half of the valve.

 

[Jason Klassen]

I suppose all the high pressures within the mcv will eventually find the weak spot in a casting if there is one, excessive heat probably doesn't help either.

I am going to run more tests when I get my gauge and palm pilot but I will keep this scenario in mind.

Does anyone know of good places to get used main control valves? I would assume the dealer doesn't have any or would be way too expensive. Just want to check into all my options.

 

[Jason Klassen]

I talked to a guy at Flemming's Equipment Services the other day. They sell used Hitachi and Deere parts and are fairly close to me. I asked if they had any main control valves for my machine because I have a hunch there might be an internal crack.
His reply was interesting... he said he did not have any in stock but that the ex120 main control valves were known for cracking.

In didn't tell him about any of the issues I am having and asked if he could explain a little more.... he said they were known for cracking through the travel ports and that they would then cause all kinds of weird travel issues.

I couldn't believe my eyes when I read that email, maybe this is finally the solution! I am going to contact the Hitachi dealer but I am expecting big money or not available.

I am kinda leery of used ones as well because what if they already have a crack or are about to crack.

Has anyone ever heard of fixing internal cracks in main control valves? Maybe by sleeving the affected bore? If one could find the crack/cracks with a bore scope maybe something could be done by a machine shop?

These are some part numbers I have found if somebody knows where a good used mcv can be found:
ex120-2 4254646
ex120-3 4338612
ex100-2 4254645
ex100-3 4339736
and the one that is actually on my mcv 4304717

 

[mg2361]

he said they were known for cracking through the travel ports and that they would then cause all kinds of weird travel issues.

Very interesting! We had a very small population of those machines (Deere anyway) in our area, so I have not heard that. That is what I love about HEF, learn something new every day.

 

[Jason Klassen]

Time to share preliminary results. The main control valve is back out of the machine. I have not found the crack yet but I did rig up a test with compressed air. I made an adapter so I could hook an air line to the inlet port where the pump feeds the mcv.

Oil flow is supposed to be blocked by all the main spools. The unload valve opens after 283 psi and relieves pressure back to the tank. I am only putting in 100 psi shop air so the entire mcv should have acted like a pressure vessel, with maybe some minimal leakage.

When the air was introduced it started coming out of all the returns and some of the travel ports surprise, surprise! Since the unload valve should not be opening at this pressure there must be an alternate route from the pressure side to the return side.

I then plugged the return ports and pressurized the mcv again. The air was defiantly coming out of all the travel ports, some more than others. I felt for it by hand and there was no air coming out of the other circuits just the travel ports.

Looks like this confirms what the thermal camera found with the travel hoses heating up at idle with the controls in neutral.

Here are some pics and a video. Hopefully I can get the video to work.

 

[Jason Klassen]

Lets see if this works...

 

[Jason Klassen]

Ok ladies and gentlemen, I tracked down a "new to me" main control valve. Got it delivered, replaced a bunch of orings, painted it and now installed it. I have not run any real tests yet but its looking promising!

I used to be able to hear a hissing sound coming from the main control valve while the machine was idling. It would fluctuate up and down, kinda intermittent but always there. Now there is no hissing, its pretty much silent in the control valve area. I am guessing that the hissing was oil bypassing through the internal crack.

The new control valve also had air leaking out the travel ports but not nearly as much. I think the air coming out the travel ports is because those ports are the only ones that are connected to the return circuit while the spools are in neutral. They don't receive pressure in neutral but they are open to return so that pressure does not build in the lines causing the parking brake to release.

I got a gauge and mounted it to the end of the air line I was using to pressure test the control valves. I could then compare the pressure at the control valve to the pressure at the regulator from the compressor. When the two numbers are divided I can get a percentage of leakage.

Cracked control valve: 32% loss
"New" control valve: 20% loss
"New" control valve after orings: 18% loss

That was a relief to see that the new one was better in some quantifiable way.

I have tried the tracks and they seems to be acting consistently. It doesn't just randomly stop anymore. I also climbed a hill on my driveway which I am pretty sure would not have been possible before. There is more testing to do and probably some tweaking of things that I calibrated while the broken control valve was in there.

Here are some pics...
Had it delivered to my work so I just backed my truck up to his power tailgate and slid the pallet in. The packaging left something to be desired.

 

[Jason Klassen]

Got it in the shop and started to strip it down.

 

[Jason Klassen]

I have not seen the DP sensor before. Anybody else seen this type? It seems to be non-adjustable.

Type. KH22
No. 370069
Range. 0-2.55 Mpa
Nagano Keikico
Made in Japan

 

[Jason Klassen]

Gotta remember to split the control valve in half and get those orings on the inside.

 

[Jason Klassen]

Fully painted and ready to install.