Mini Excavator Control Problems

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bremery

Well-known member
Joined
Feb 6, 2008
Messages
59
I picked up a Scat Trak 530 mini excavator with pilot controls. The machine runs great but has hydraulic control problems. The problem is the boom, bucket, and crowd operations are slow or barely work, unless you operate a function on the opposite joystick at the same time. The left side drive track is stuck but the right seems to move as long as you are operating another function. It appears the control block is divided into three segments. One being, turntable, blade, and offset boom (This group works fine). Second being Right track, bucket, and aux, and a third being boom, left track and crowd.
When you try one function all by it self it sounds like a relief valve is opening, not sure which one, port or main relief. I have checked the three main reliefs to see if they are stuck and they appear to be in working order. I have also moved the relief from the working circuit (Blade and offset boom, and turret control) but that did not have any effect on anything. The guy I bought it from had the pumps tested and they are within spec. All of the electrical solenoids are getting power and seem to be working.
Any ideas on where to go next?
 

Dirtwise

Member
Joined
Jun 16, 2009
Messages
13
Check the pilot system for filter's right before the valve banks, make sure there clean and not half way plugged ( this will do funny thing's) with the flow. Next check the cap's on the bottom of the spool's for rust ( like the maching was sitting under water).
 
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bremery

Well-known member
Joined
Feb 6, 2008
Messages
59
Check the pilot system for filter's right before the valve banks, make sure there clean and not half way plugged ( this will do funny thing's) with the flow. Next check the cap's on the bottom of the spool's for rust ( like the maching was sitting under water).
I do not see any obvious filters near the valve bank. Would these look like a regular inline filer or something smaller? I am in the process of cleaning the in tank and inline hydraulic filter.
 

Land-Tech

Well-known member
Joined
May 13, 2008
Messages
160
I do not see any obvious filters near the valve bank. Would these look like a regular inline filer or something smaller? I am in the process of cleaning the in tank and inline hydraulic filter.
I think the filters that Dirtwise is refering to are inside the fitting housing and are small.I've heard that might be a common problem too.
If your machine is newer and has a iso/std converter or switch that controls the joystick function. Mine is is a lever and if you have one it might be out of position. Thats what I thought of first but probably doesn't apply.
Do you know if it open or closed center valving and where the supply lines are in relation to the controls that function?. Checked the pilot pressures? Has some one repaired the machine and maybe got a line or two backward? I'm just guessing . Fishfiles or one of the mechanics on the site could be be more help, at least ask the right questions..Scott
 
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bremery

Well-known member
Joined
Feb 6, 2008
Messages
59
I think the filters that Dirtwise is refering to are inside the fitting housing and are small.I've heard that might be a common problem too.
If your machine is newer and has a iso/std converter or switch that controls the joystick function. Mine is is a lever and if you have one it might be out of position. Thats what I thought of first but probably doesn't apply.
Do you know if it open or closed center valving and where the supply lines are in relation to the controls that function?. Checked the pilot pressures? Has some one repaired the machine and maybe got a line or two backward? I'm just guessing . Fishfiles or one of the mechanics on the site could be be more help, at least ask the right questions..Scott
I picked up some fittings and a pressure gauge today to check the pressures at the pilot control pressure reducing manifold. I plumbed the gauge into the port where the hoses come in from the valve block. I found out the three main relief valves were set high, so I adjusted these to what the manual said to. The dozer blade, offset boom and turntable is set to 190 Bar, and the other functions are set to 210 bar (My hydraulic circuit diagram shows them all being 190 bar, which is a little different than what the procedure says). At full throttle and moving nothing I get about 300 psi. When I move a single function the pressure jumps up to what I set the relief at.

I then moved the pressure gauge to port right at the pilot lines that go joysticks. I get little to no pressure at max engine rpm and no functions being operated. When I try a function the gauge will read 600-700 psi. The spec is 400 to 545 psi. This is a little high and I need to adjust this. I got it pretty close on my first attempt, but rain out of day light.

I need to get a tee fitting to verify I am getting 500 or so psi to the spools. I also changed the hydraulic fluid and cleaned the in tank filter. It was pretty clean to begin with. I did not replace the main hydraulic filter as I got the wrong one from the parts store. I am getting the correct one tomorrow and will put that to see if that helps.

After getting the fluid warm, the hoses get warm and the filter gets warm, but the return hose to the tank does not get warm. I am hoping my filter is clogged up.

I believe my problem is flow related, but I am running out of ideas. What about air in the system? Can that cause airlocks? Can it be bleed.

Thanks for everyone's help so far.
 
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bremery

Well-known member
Joined
Feb 6, 2008
Messages
59
I picked up some fittings and a pressure gauge today to check the pressures at the pilot control pressure reducing manifold. I plumbed the gauge into the port where the hoses come in from the valve block. I found out the three main relief valves were set high, so I adjusted these to what the manual said to. The dozer blade, offset boom and turntable is set to 190 Bar, and the other functions are set to 210 bar (My hydraulic circuit diagram shows them all being 190 bar, which is a little different than what the procedure says). At full throttle and moving nothing I get about 300 psi. When I move a single function the pressure jumps up to what I set the relief at.

I then moved the pressure gauge to port right at the pilot lines that go joysticks. I get little to no pressure at max engine rpm and no functions being operated. When I try a function the gauge will read 600-700 psi. The spec is 400 to 545 psi. This is a little high and I need to adjust this. I got it pretty close on my first attempt, but rain out of day light.

I need to get a tee fitting to verify I am getting 500 or so psi to the spools. I also changed the hydraulic fluid and cleaned the in tank filter. It was pretty clean to begin with. I did not replace the main hydraulic filter as I got the wrong one from the parts store. I am getting the correct one tomorrow and will put that to see if that helps.

After getting the fluid warm, the hoses get warm and the filter gets warm, but the return hose to the tank does not get warm. I am hoping my filter is clogged up.

I believe my problem is flow related, but I am running out of ideas. What about air in the system? Can that cause airlocks? Can it be bleed.

Thanks for everyone's help so far.
To follow up. I have solved my problem. The previous "Mechanic" must have taken the main valve block apart and installed the internal checks backwards. This did not allow for any flow to that function group, and would only build pressure to open the pressure reliefs. Very fustrating, but I am back in action.
 

Tazza

Moderator
Staff member
Joined
Dec 7, 2004
Messages
16,829
To follow up. I have solved my problem. The previous "Mechanic" must have taken the main valve block apart and installed the internal checks backwards. This did not allow for any flow to that function group, and would only build pressure to open the pressure reliefs. Very fustrating, but I am back in action.
Glad you got it sorted. It wouldn't have been easy to work that out! its not something you'd think would be wrong, especially if you didn't know someone had "worked" on it before.
 

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