Mini Excavator Hydraulic Problem

[vongiese]

Hi - I have a 2016 Sany SY35 excavator with 350 hours. I bought it used a year ago. It is a 8500lb machine. The Boom deflection cylinder does not work. This cylinder pivots the boom at up to 90 degrees either direction from the cab so you can dig close to buildings, etc. It is operated by a foot pedal, and when I push on the pedal nothing happens - no whine from the pump - nothing. I pulled to pedal spool valve and blew low pressure air thru all orifices (couldn't figure out how to take it apart) and all seemed clear. This valve has no solenoids. I'm stumped. All other hydraulics work normally. I don't normally need to pivot the boom, but it has slowly moved and is off angle now. Even in the interim, if I could find a way to straighten out the boom I'd be happy!
Seems like it should be something simple....
thanks for any help.
VG

 

[dfkrug]

Sany may be the most common mainland Chinese excavator brand in the US. There seems to be west coast importers
in WA and SoCal.

First Q on your hyd problem: how many hyd pumps does it use?

Then: does the maker provide any hyd schematic docs?

 

[vongiese]

Thanks for the reply dfkrug - There is one pump and I have the hydraulic schematics...attempting to attach it....THe cylinder is labeled "BOOM SWING".
VG

 

[MossRoad]

If it were me, I'd swap the hoses for that cylinder with the hoses for another cylinder to quickly check if it's the valve.

 

[dfkrug]

Yeah, only one pump...looks like a variable-displacement pump.

My guess is that the nut fell off the rod inside the cyl, or the valve spool is faulty. I lean toward the latter, which
you can isolate with some hose-swapping as MOSS says.

If the valve, you may be able to slide the spool out without removing the whole valve stack. I was able to on my Chinese mini-X.

Let's hope it is the nut.

 

[vongiese]

Yeah, only one pump...looks like a variable-displacement pump.

My guess is that the nut fell off the rod inside the cyl, or the valve spool is faulty. I lean toward the latter, which
you can isolate with some hose-swapping as MOSS says.

If the valve, you may be able to slide the spool out without removing the whole valve stack. I was able to on my Chinese mini-X.

Let's hope it is the nut.

I'll swap hoses today and let you know what happens. Thanks for the advice MossRoad and dfkrug!!!
vg

 

[vongiese]

Yeah, only one pump...looks like a variable-displacement pump.

My guess is that the nut fell off the rod inside the cyl, or the valve spool is faulty. I lean toward the latter, which
you can isolate with some hose-swapping as MOSS says.

If the valve, you may be able to slide the spool out without removing the whole valve stack. I was able to on my Chinese mini-X.

Let's hope it is the nut.

Thanks for the advice MossRoad and dfkrug. I'm attempting to swap hoses today and find that adjacent hose fittings are all a larger size than the boom swing fitting. See the attached pic - it's the fitting with writing on it...hard to tell from the photo but if you look close you can see it is smaller than the rest. And the logical one to swap with is the thumb which is the very large one to the left. And I don't have stubby wrenches that can get at those fittings. Might be forced to take it to a repair shop....the machine is still under warranty - I just wanted to make sure it's not something simple and or not covered under warranty (i.e. dirt clogging a valve) etc. Any other ideas?
vg

 

[MossRoad]

Of course it's smaller. Why would life throw me a bone and make them all similar? :laughing: Well, it was worth a shot. You could get adapters for the size. But as you said, it's still under warranty.

 

[MossRoad]

What's the one just to the right of the one with the writing?

 

[vongiese]

The hose to the right is for the house swing, and it is slightly larger than the boom swing hose....
vg

 

[dfkrug]

Clearances on the stack valve are often such that the hoses have to be attached sequentially. Not easy to do just one!

Is your dealer in Seattle, or does someone in MT handle Sany? Missoula, maybe?

 

[BertZegers]

Put the bucket on the ground, pull the boom swing lever (try both ways) to allow the the oil to move in the boom swing cylinder, use the track (turning) levers to straighten the boom.
Maybe it works.

 

[BertZegers]

I sometimes have a hydraulic problem with my Kubota KX41 excavator. Than the boom cylinder and one of the tracks will not work. They share the same relief valve. After I open the cover-nut on the boom valve (engine off) and put it back on, the machine works again.

You indicate that the engine does not work harder and there is no whine (from a relief valve) if you activate the boom swing cylinder. So I think the check or relief valve for the boom swing valve is stuck open.

 

[kthompson]

I have a Volvo mini and on mine there is a button on the left joy stick that switches between upper structure and the boom swinging. It is my guess your machine is similar. For safety reason doubt both circuits are powered at the same time. You did not mention having manual that I noticed, might find one on line or a youtube review or such for operation of your machine.

 

[kthompson]

Took me a while to find even this much but read very carefully on the pedals. On same page it tells the joy sticks rotate the upper structure. Could you be using the wrong foot pedal? Maybe linkage is not adjusted properly or not connected.


5.If you want to accelerate the machine, step on the small pedal on the left of the floor board, which is the high speed control and boosts the drive pump. The pedal on the right side is used to pivot the mini excavator痴 hoe left and right. Keep in mind that these two controls can only be used on stable and level terrain, otherwise it may case the tipping over of the machine.

 

[vongiese]

Clearances on the stack valve are often such that the hoses have to be attached sequentially. Not easy to do just one!

Is your dealer in Seattle, or does someone in MT handle Sany? Missoula, maybe?

It looks loke it would be tough to do without doing all sequentially - thanks for pointing that out. The machine was purchased in Washington at Kitsap - west of seattle. I bought it used a year ago. According to the dealer I can take it to any equipment repair shop and they will reimburse. At least thats what they told me before I bought it. Going to call the dealer again to clarify. I'm near Troy and there are a couple shops in Libby. Prefer to do it myself, but....
Appreciate the feedback!

 

[vongiese]

Put the bucket on the ground, pull the boom swing lever (try both ways) to allow the the oil to move in the boom swing cylinder, use the track (turning) levers to straighten the boom.
Maybe it works.

I already tried that with no luck....

 

[dfkrug]

Since the SY35 has only one pump, there will be only one shared system relief valve. Most modern excavators (even the small ones) have 2 or more pumps, each with a system RV. I do see several work-port RVs on your unit. That is good.

You can determine if oil is flowing to your swing cyl by holding the hose when activated. You will feel the flow. Be careful doing this, of course. You do not want to get squished if it starts working suddenly. If the valve was is some way blocked, you would hear the RV and the engine sound change.

 

[vongiese]

I sometimes have a hydraulic problem with my Kubota KX41 excavator. Than the boom cylinder and one of the tracks will not work. They share the same relief valve. After I open the cover-nut on the boom valve (engine off) and put it back on, the machine works again.

You indicate that the engine does not work harder and there is no whine (from a relief valve) if you activate the boom swing cylinder. So I think the check or relief valve for the boom swing valve is stuck open.

BertZegers - I think you are on to something....no whine when i try to move boom swing cylinder. Check or Relief valve?....Would have to one one that is only for the boom cylinder right? (I'm learning). You know the dealer service guy said to check the oil source control valve - there are 2 solenoids - but didn't say how to test them, then reconsidered the symptoms and said it's prolly a clogged valve...at that point (had made a total of 13 phone calls to them about this) - I gave up one them. I tested the solenoids...and there was voltage to each (would have to find my papers to get numbers). Manual doesn't list any testing parameters for voltage or resistance for the oil source control valve solenoids. Hmmmm....

 

[vongiese]

Since the SY35 has only one pump, there will be only one shared system relief valve. Most modern excavators (even the small ones) have 2 or more pumps, each with a system RV. I do see several work-port RVs on your unit. That is good.

You can determine if oil is flowing to your swing cyl by holding the hose when activated. You will feel the flow. Be careful doing this, of course. You do not want to get squished if it starts working suddenly. If the valve was is some way blocked, you would hear the RV and the engine sound change.

I'll try that tomorrow dfkrug -- great idea. So then if I have oil flow - must be the cylinder?
vg