EX120-2 system base pressure too low

[Jason Klassen]

Hey everyone, I am looking for some more brain power with this problem.

Machine is a 120-2 with what I believe to be a 120-3 main control valve (mcv). This means it does not have the adjustable pressure regulator on top of the unloading valve like the -2. Its on the bottom instead.

According to the manual the differential pressure (dp) sensor needs to see 370 psi or more to signal the pump to run at minimum displacement while at idle. This 370 psi is set by the spool and spring in the unloading valve.

My DR.Zx shows that its making ~250 psi at idle and the angle of the pump is 6-7 degrees.

If I unplug a sensor and get the machine to run at max displacement (24 deg) at idle, the pressure increases to 480psi.

As far as I can tell this "base" pressure of 370 psi is set purely in a physical way by the unloading valve. There should be no sensors involved since the dp sensor is looking for 370 psi or more to set the pump angle to the minimum of 3 deg.

I have tried shimming the spring in the unloading valve to increase the pressure but it made no difference. There must be some sort of internal leak in the mcv. The pump is brand new inside so I don't expect it to be weak.

Any thoughts are apricated.
Jason

 

[mg2361]

@LACHAU ......Help!!!!!

 

[Jason Klassen]

Anybody?

Thanks for the thread bump mg2361. I tried to pm LACHAU but I don't know if it worked.

 

[mg2361]

As far as I can tell this "base" pressure of 370 psi is set purely in a physical way by the unloading valve. There should be no sensors involved since the dp sensor is looking for 370 psi or more to set the pump angle to the minimum of 3 deg.

Just a thought. I think the 370 psi is 370 differential, so if it is low (250), then maybe there is leakage somewhere allowing more pressure on the load sense side of the Dp?? Unfortunately, I don't know of any ports to actually test those pressures with a gauge.

I have tried shimming the spring in the unloading valve to increase the pressure but it made no difference.

If there is leakage like I mentioned, then increasing pump pressure will increase load sense pressure so the differential will be the same??

 

[Jason Klassen]

Hmm, that does make some sense, I am going to try setting all the circuit relief pressures. Hopefully there is one that is bleeding off pressure. While the machine is idling I can hear a hissing noise coming from the main control valve area. It's not loud and it sometimes fluctuates.

 

[LACHAU]

Hey everyone, I am looking for some more brain power with this problem.

Machine is a 120-2 with what I believe to be a 120-3 main control valve (mcv). This means it does not have the adjustable pressure regulator on top of the unloading valve like the -2. Its on the bottom instead.

According to the manual the differential pressure (dp) sensor needs to see 370 psi or more to signal the pump to run at minimum displacement while at idle. This 370 psi is set by the spool and spring in the unloading valve.

My DR.Zx shows that its making ~250 psi at idle and the angle of the pump is 6-7 degrees.

If I unplug a sensor and get the machine to run at max displacement (24 deg) at idle, the pressure increases to 480psi.

As far as I can tell this "base" pressure of 370 psi is set purely in a physical way by the unloading valve. There should be no sensors involved since the dp sensor is looking for 370 psi or more to set the pump angle to the minimum of 3 deg.

I have tried shimming the spring in the unloading valve to increase the pressure but it made no difference. There must be some sort of internal leak in the mcv. The pump is brand new inside so I don't expect it to be weak.

Any thoughts are apricated.
Jason

1/- You should try to adjust the DP sensor (It's adjustable).
2/- I suggest you double check. That means you will use a differential pressure gauge to check if the value of differential pressure is correct as shown by Dr.ZX.

 

[mg2361]

2/- I suggest you double check. That means you will use a differential pressure gauge to check if the value of differential pressure is correct as shown by Dr.ZX.

Could you please supply a picture/drawing of the port locations?

 

[Jason Klassen]

1/- You should try to adjust the DP sensor (It's adjustable).
2/- I suggest you double check. That means you will use a differential pressure gauge to check if the value of differential pressure is correct as shown by Dr.ZX.

Hi LACHAU,

1) I have adjusted the DP sensor. I have a workshop manual for the excavator and in there it shows how to take apart the DP sensor and gives a specification for the adjustment. I attached a couple of pics. It said 0.4V so that is what I adjusted it to but I have read in different threads that some people are adjusting them at 1.0V - 1.4V. While adjusting it I put a smaller allen key into the hole in the end and pushed on the piston. If I pushed hard enough I could get the multimeter to read 4.5V.

I also bought an aftermarket DP sensor, but when I installed it all the 5V sources for the other sensors went dead including the communication connector for Dr.Zx. When I changed to the old DP sensor all the 5V sources came back and I could get Dr.Zx to communicate again. It turns out that the new DP senor has a short to ground internally. The 5V source is going directly to the ground wire and leaving only 0.29V behind on the signal line. For some reason that affected all the other 5V sources on the machine.

2) I recently had the entire main control valve apart for cleaning/re sealing with new o-rings. If I remember right there were two plugs nearby the DP sensor. One above it on top of the mcv and another partially hidden behind the DP Sensor. I could be wrong. When I had it apart it was hard to tell if they would be useful or not. A diagram of some kind would be great!

 

[timbercutter]

) I recently had the entire main control valve apart for cleaning/re sealing with new o-rings.

Did the problem start immediatley after this? If everything was not put back together exactly as it came out this could be a cause of your problem. I had a valve bank resealed and one little piece was put in upside down and it caused a hair pulling scenario which I wont bore you with. Long story short it took a retired hitachi mechanic 3 days of running tests to figure out the problem. I ended up with all new sensors as well. The hydraulics on these machines are really finicky the way they are designed, everything has to be in order.

 

[Jason Klassen]

Hi timbercutter,

The problem started before I took the mcv apart. I was very careful to put it all back the way it came out. I bought the machine with lots of issues and I am now at the point where most of them are fixed and this is the last major one. I am going to try setting all the relief pressures this weekend. According to the info I got from mg2361 this could be the problem.

I find it funny how in the manual it says that when you take a relief valve apart you are supposed to measure the height of the set screw so you can put it back properly. The problem is that 1/8 of a turn is equal to 300 psi and the screw is fine thread. They could be way off and you wouldn't know by measuring let alone looking at them. I have not messed with the adjustments on the relief valves but it looks like other people might have been in there, so hopefully adjusting them makes a difference.

Are you located anywhere near me? Would this retired Hitachi mechanic like to look at my machine? Joking, but kinda serious haha.

 

[LACHAU]

Could you please supply a picture/drawing of the port locations?

sorry for the late reply! I repaired these machines a long time ago! So it took me a long time to rummage through the notes!!!

You measure the pressure at the place marked in the picture and compare it with the pressure of the main pump.

 

[LACHAU]

Hi LACHAU,
... It said 0.4V so that is what I adjusted it to but I have read in different threads that some people are adjusting them at 1.0V - 1.4V. While adjusting it I put a smaller Allen key into the hole in the end and pushed on the piston. If I pushed hard enough I could get the multimeter to read 4.5V.

Where did you read that?? So have you tried adjusting to that value? It's been a really good experience.
Try setting it to 1 Volt .

 

[Jason Klassen]

Alright, I set the dp sensor to 1.0V. At idle the pump angle used to be 6.7 - 7.3 degrees. After the adjustment the pump angle is 8.2 - 8.4 degrees. That's the only difference it made, the overall pressure did not increase. I believe the spec is 3 degrees at idle, (controls in neutral) and 5 degrees in P mode (controls in neutral).

I pulled the pump angle sensor and turned it by hand. The full range from 0-24 degrees displayed on Dr.Zx. I hooked up a new angle sensor and it also went from 0-24 degrees. I installed the new one anyway. Unplugged the pump solenoids and let the angle fall to 24 degrees. Then set the angle sensor to 4.47V by back probing it. Fired the machine up and got the same 8 degrees at idle.

I tried to to set the relief valves today.

1- turn up main relief a couple of turns
2- bring rpm to 1700 and oil temp to 50C ( I only got to 40C)
3- adjust circuit reliefs by holding each function over relief and then adjusting (1/8 turn = 300 psi) (measure at pump with gauge or Dr.Zx)
4- then adjust main relief back down to where it was

My brother and I started making the adjustments but the pressure never increased. By the end we turned all the circuit reliefs and the main relief all the way in until the adjustment screws got tight and there was no increase in pressure from any function being tested.

The only reliefs we did not touch were the swing motor and the travel motors. They were not part of the procedure mg2361 gave me.

Should we do something to them also?

- The gauge showed 3600-3800 psi (looking for 5000psi)
- Dr.Zx showed 3000-3500 psi (21-24 Mpa) ( I have replaced the sensor, the old one read the same)
- The lowest I saw was 2750-2900 psi (19-20 Mpa) when I tried to turn and the tracks stopped moving. Turning left or right has the same result. It will start to turn and then just stop, probably due to the very low pressure.


I had all the shuttle valves apart when I cleaned and checked the mcv. They were all good. The diagram looks like it is pointing to the plug that covers shuttle valve #7. That plug only holds the shuttle valve in. How would I connect a gauge to that location?

Thanks for your help LACHAU! I appreciate you taking the time to go through your old notes.

 

[Jason Klassen]

Still trying to track this problem down.

In the procedure for setting the relief valves it only talks about adjusting the ones that are located within the main control valve (mcv). It does not mention setting the travel or swing reliefs.

I also have information that says, if any of the circuit reliefs are set lower than the main relief, that circuit relief will then act as the main relief.

That makes sense for the circuit reliefs that are located inside the mcv but what about the travel motors and swing motor? Will their reliefs affect the overall pressure if they are set lower than the main relief?

 

[mg2361]

Will their reliefs affect the overall pressure if they are set lower than the main relief?

Only when the swing or travel are activated will their reliefs affect the system if they ate set lower.

 

[John C.]

Swing and travel reliefs are in the motors themselves and not in the main control valve.

 

[Jason Klassen]

Ok, that makes sense, just trying to cover all the angles.

How do I go about checking the pressure at #7 shuttle valve? I am sure that it is just blocked off by a plug. There are two other ports that I will try to describe with pictures below.

These are from when I took apart the mcv.

 

[mg2361]

That plug next to the Dp sensor is connected to load sense pressure. There is a screen in there to keep any debris that may be in the load sense oil from contaminating the Dp sensor.

Yes, that hose is the drain for the end of the Dp sensor and is not connected to any pressure.

 

[Jason Klassen]

Ok, I got a little side tracked and rebuilt all the circuit relief valves and the main relief valve. All of them are still cranked down all the way and the most pressure I can get in any function when held over relief is 3600-3800 psi.

I still plan on checking the load sense port but it is blocked by the dp sensor body and will require a special connector or some creativity to get a gauge on it.

I am coming back to the low system base pressure issue because it has got to be related to the rest of it.

I back probed the dp sensor plug with the machine at idle and the controls in neutral and got 2.8-3.0V. It should be 4.5V with all the controls in neutral. The picture below from the manual explains it pretty well. I took a jumper wire and jumped the 5V source over to the signal line that goes back to the pvc controller. As soon as I touched the jumper wire to the signal line I could here the engine idle smoother and the pressure line flexed so I know the pump was being de-stroked. I believe the dp sensor is working fine.

According to the manual the pressure at idle is set by the unloading valve at 370 psi. DrZx shows the pressure to be 1.6-1.9 Mpa (230-275 psi). I have a gauge plumbed in at the pump also but the needle barely moves. It is a 0-3500 psi gauge so I should be able to see 370psi on it.

At idle with the controls in neutral the pressure that is seen on the gauge and the pressure at the dp sensor should be what the unloading valve is setting it at, since there should be no load sense acting on the dp sensor in neutral.

The pressure in neutral is blocked by the main spools. The pressure then builds until it overcomes the spring in the unloading valve and returns to the tank. I have shimmed the unloading valve before with no increase in pressure.

So either the pressure is getting by one of the main spools or the pump is not putting out enough flow to build the pressure required. I have had the pump apart though and the previous owner was not lying when he said the pump had been recently rebuilt.

Any thoughts? Please let me know if I am understanding this all wrong.

 

[Jason Klassen]

I got a new main relief valve from the Hitachi dealer on the weekend and installed it. Nothing changed, ! I had talked to a few local people and they suggested changing the main relief. I just went through the main and circuit reliefs with all new o rings but I thought I would give a new relief a chance since they were telling me how touchy relief valves can be.

Weird thing happened after I put all the valves back in, the thumb stopped working properly. It closes with some force but not like before and it can not open. I can see the cylinder rod move but it stops as soon as it feels the weight of the thumb.

- checked the pilot pressure, 600 psi to top and bottom of the spool.
- checked the spool, it moves freely.
- took one line off the cylinder and tried to raise the thumb, a little oil came out and then nothing so its not bypassing the piston seals inside the cylinder.
-pulled the circuit reliefs for the thumb back out and nothing seems to be stuck.

Also the tracks are even slower to respond now. If I grab both levers and pull or push them all they way there is a 5 second delay before they start moving. They start slow and then pick up speed.