Mini Excavator Hydraulic Problem

[BertZegers]

If you look in the hydraulic diagram you can see that the boom swing valve (PB5) has the same pressure and return lines as the other valves. I think we can conclude there is not a problem there. If the cylinder has a internal leak, it would not hold position and the boom would swing with outside force (you tried with the undercarriage). I also think the boom swing cylinder is not the problem.

If we look at the diagram at PA5 and assume that the check valve is in the open position, then when the valve is operated, the pressure oil would flow freely back to the tank, this would make the boom swing inoperable, and no whine, no extra engine power, no hose flex would show.

If you follow the small hose of the boom swing valve, does it lead to PA5? PA5 has a check valve and a orifice in it. Some dirt can make it fail.
PA5 seems to be a pilot valve for PB5 (the swing boom valve).

I am in no way a hydraulic mechanic, but I learned to diagnose faults by reading schematics, I hope to be of help.

 

[vongiese]

If you look in the hydraulic diagram you can see that the boom swing valve (PB5) has the same pressure and return lines as the other valves. I think we can conclude there is not a problem there. If the cylinder has a internal leak, it would not hold position and the boom would swing with outside force (you tried with the undercarriage). I also think the boom swing cylinder is not the problem.

If we look at the diagram at PA5 and assume that the check valve is in the open position, then when the valve is operated, the pressure oil would flow freely back to the tank, this would make the boom swing inoperable, and no whine, no extra engine power, no hose flex would show.

If you follow the small hose of the boom swing valve, does it lead to PA5? PA5 has a check valve and a orifice in it. Some dirt can make it fail.
PA5 seems to be a pilot valve for PB5 (the swing boom valve).

I am in no way a hydraulic mechanic, but I learned to diagnose faults by reading schematics, I hope to be of help.

BertZegers - You are a huge help! yes- the small hoses from boom swing pedal go to PA5 and PB5 ("P" must be for pilot) these are on either end of the valve body; the A5 and B5 are the larger hoses coming out of the top of the valve to the boom swing cylinder. And you're right - I can't feel oil going thru hose when activated like suggested earlier. So now how to clean it out? Looks like I can remove a side body panel off the exc. to access the side of the main valve. There are covers over each pilot and looks like I could pull out the spool? I'll go mess with it. --- - or pull all 34 some odd hoses and remove the entire valve? ugh!

 

[vongiese]

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.

kthompson - - i have all the manuals for this excavator. Boom deflection cylinder should work by pedal alone. The info you found must be for a different machine...mine has non of that. But thanks for trying!

 

[BertZegers]

You say " the small hoses from boom swing pedal", but the diagram shows that the pedal is connected to the valve by a linkage.

I would locate the PA5 body and go from there. (loosen one line and bleed some oil, than the other) if that doesn't do the trick, see if there is a cap screw hiding the check valve / orifice / springs /o rings. A small piece of rubber from a damaged o ring can cause the problem.
Be very careful with the high pressure, don't be close if there is a risk from pressure oil escaping, sometimes invisible! It can penetrate your skin and cause severe damage to your body!
I would not take more apart than necessary, to prevent dirt from entering the system.
Good luck.

 

[vongiese]

You say " the small hoses from boom swing pedal", but the diagram shows that the pedal is connected to the valve by a linkage.

I would locate the PA5 body and go from there. (loosen one line and bleed some oil, than the other) if that doesn't do the trick, see if there is a cap screw hiding the check valve / orifice / springs /o rings. A small piece of rubber from a damaged o ring can cause the problem.
Be very careful with the high pressure, don't be close if there is a risk from pressure oil escaping, sometimes invisible! It can penetrate your skin and cause severe damage to your body!
I would not take more apart than necessary, to prevent dirt from entering the system.
Good luck.

The pedal controls a valve - all hydraulic - 4 hoses to it....one from pump, one to tank, and the two that go to PA5 and PB5 at to the main valve pilots. I'll see what I can do by bleeding some oil and trying to get at the check valve....dark now so will have to wait til tomorrow. I appreciate your help!!! I'm a newbe with hydraulics.
VG

 

[BertZegers]

The diagram does not show the hoses PB5 and PA5 from the pedal to the valve block! That is why I thought the valve was operated with a linkage, and read the diagram WRONG!

With the pedal you direct oil to the boom swing valve through hose PB5 or PA5, pushing the spool to "work" position.

Because the swing valve is activated by oil pressure through the pedal, you could "bleed" the lines at the pedal end first, see if there is oil pressure at the pedal.

 

[vongiese]

The diagram does not show the hoses PB5 and PA5 from the pedal to the valve block! That is why I thought the valve was operated with a linkage, and read the diagram WRONG!

With the pedal you push oil to the boom swing valve through hose PB5 or PA5, pushing the spool to "work" position.

Because the swing valve is activated by oil pressure from the pedal, you could try to bleed the lines at the pedal end first.

I apologize for the misleading diagram!! So by bleeding - just take off the hose and let some oil flow out? The reason I ask is I had the lines to the pedal off once and not much came out (one of the first things I did was I removed the pedal valve and blew some low pressure air thru all orifices while operating valves to clean out any clogs). thanks, vg

 

[BertZegers]

This is how it works on my excavator;

The floor pedal changes the function of the swing lever. The floor pedal in one position makes the lever turn the excavator on the turntable (activates the swing motor). The other function makes the excavator work as a backhoe (activates the swing cylinder). You use the same lever 2 functions.

After reading your first post again, I am not sure of you tried it this way.

 

[BertZegers]

I apologize for the misleading diagram!! So by bleeding - just take off the hose and let some oil flow out? The reason I ask is I had the lines to the pedal off once and not much came out (one of the first things I did was I removed the pedal valve and blew some low pressure air thru all orifices while operating valves to clean out any clogs). thanks, vg

Bleeding is probably not the right term. I would find the pressure hose on the pedal valve, break the fitting loose, start the engine and loosen the nut further till oil squirts out. If there is no pressurized oil, then there is a problem "down stream".(towards the pump)
If you have pressure than loosen a pilot hose nut on the swing cylinder (PB5 or PA5) and test if the pedal sends pressurized oil to activate the swing cylinder valve.

The oil will make a mess! Have rags ready to soak the oil. Protect yourself from pressurized oil!

 

[vongiese]

Bleeding is probably not the right term. I would find the pressure hose on the pedal valve, break the fitting loose, start the engine and loosen the nut further till oil squirts out. If there is no pressurized oil, then there is a problem "down stream".(towards the pump)
If you have pressure than loosen a pilot hose nut on the swing cylinder (PB5 or PA5) and test if the pedal sends pressurized oil to activate the swing cylinder valve.

The oil will make a mess! Have rags ready to soak the oil. Protect yourself from pressurized oil!

BertZegers - Thanks for the bleeding tips - like I said I need all the help I can get -- i'm a noob wit hydraulics. I'd like to buy you a beer or two. I will do that type of bleeding going downstream to find the problem area. Sounds messy but whatareyougonna do? Been raining all day today and have to ski patrol tomorrow so won't get back to it til sat.
vg