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

 

[vongiese]

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.

I tried this but no luck. Never hurts to try!!
vg

 

[kthompson]

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!

You are welcome. Often I find the issue with such is so simple...normally just over looked. Do you have the operator's manual and is it clear the boom swing cylinder is totally and only needing the foot pedal for it's operation? By chance will the foot pedal lock in up or down position or does it just return to center? If it will lock in up and down is it possible up or down is for one for the boom cylinder and the other for rotation of the super structure? Or if it pops back to a position when you release it it is normally closed so the superstructure rotates and when you hold it open or closed as the case may be it operates the boom swing cylinder? Have you tried holding the swing level where it operating the swing and working the foot pedal to see if it operates the boom swing cylinder?

 

[vongiese]

You are welcome. Often I find the issue with such is so simple...normally just over looked. Do you have the operator's manual and is it clear the boom swing cylinder is totally and only needing the foot pedal for it's operation? By chance will the foot pedal lock in up or down position or does it just return to center? If it will lock in up and down is it possible up or down is for one for the boom cylinder and the other for rotation of the super structure? Or if it pops back to a position when you release it it is normally closed so the superstructure rotates and when you hold it open or closed as the case may be it operates the boom swing cylinder? Have you tried holding the swing level where it operating the swing and working the foot pedal to see if it operates the boom swing cylinder?

i agree - it's usually the simple stuff that I over look and this machine is new to me so I appreciate all the tips. I have all the manuals and even the label on the pedal shows that is the only function of the pedal. it has a guard that you can flip down so the pedal can't be operated inadvertently during regular operations. Keep the ideas coming tho - I appreciate it.
vg

 

[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.

Bled and determined pedal valve is working. Tried to bleed one Port on Control valve (port B5 to Boom swing cylinder - see attached) and nothing. Didn't try the other port (A5) to cylinder - figured it wouldn't show any squirting oil either. I can access one side of the main control valve body to get at releif valve the "B" side on attached diagram. Looks like this would get me to the LS Relief Valve and maybe at the spool on B side. Any ideas what the likely culprit is? I'm going to start with the relief valve and then up to the spool. VG

 

[kthompson]

vongiese,

I know you said you can not remove hoses from valve to test so remove from the cylinder. If you can use standard hoses from tractor supply or such (reason you may not be able to is fittings, may or may not find fittings you can use to connect the hoses to the hyd cylinder). "IF" you have a tractor with remote hyd on it you can connect to there and test the cylinder at least. If you break the hose fittings on the cylinder you probably will be able to move the boon back in line and then reconnect the hoses to hold in place.

I think your latest post you mentioned there is linkage from pedal to valve...be sure when the pedal is moved the linkage is moving the valve spool. You should verify that before doing any thing else. Even if it is moving it be sure it is moving it enough to operate.

I worked as inspector for a hyd crane company and inspected and we first one to operate the machines as they came off the assembly line. Not saying we never had defective valve bank or relief valve but very very seldom. Holding valves once in while but probably those were little piece of trash in them.

Hope you well in this. KT

 

[BertZegers]

I think you have narrowed it down to the control valve, LS flush valve / LS relief valve or cylinder.
The cylinder is the last I suspect because if you had pressure at port B5 the cylinder would move, or at least the B5 hose would stiffen.
That leaves the control valve or LS flush valve / LS relief valve as culprit. It looks that the LS flush valve / LS relief valve is a unit separate from the control valve.
Clean valves and put together with hydraulic oil. Easiest first. I hope it solves the problem.

 

[vongiese]

It's been snowing and raining so haven't worked on it til today (Need a taller shop).
I attached a diagram - the valve I'm working on is on the left. I refer to the part numbers here -
I was able to pull out plug 4 and the small spool on the relief valve 45 all looked OK.
Then I pulled off the cover and seat and spring 22 and 31. I could not budge the spool 43! Pushed and pulled on it and nothing. do I need to take off the other hoses? How aggressive should I get? Obviously my problem area..... Do I have to take off the other cover (same cover as 46 but on opposite side)? To get at that other side of the valve body I might have to take most of the hoses off...
thanks for any advice
VG

 

[laurencen]

usually the spool will move, its double acting so nothing should be holding it, you could take the spool next to it and see if its also tight, had a bobcat 846, the spool was stuck, turned out it sat with water in the valve and solid, took a bit of force to free it

 

[vongiese]

usually the spool will move, its double acting so nothing should be holding it, you could take the spool next to it and see if its also tight, had a bobcat 846, the spool was stuck, turned out it sat with water in the valve and solid, took a bit of force to free it

This machine is only 2.5 years old and 350 hours so i wouldn't think rust? I didn't want to tap on the spool with a rubber mallet until I asked someone....I sure could try another spool to see if it comes out, but they should be free moving...this one isn't and that is my problem. will i damage the spool or body?
vg

 

[BertZegers]

I would tap the spool to see of it moves. If it moves in and the spring doesn't push it back than you have to take more apart to get the spool out on the other side.

If you use some sort of soft metal as a punch as you tap the spool you probably wont damage it.

Is there some way to use hydraulic pressure to push the spool out on the port of 46 (from opposite site)?