Hydraulic Problem With Pilot Controls

[bremery]

I recently 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?

 

[Muffler Bearing]

Does it have 3 pumps? Left track, right track and functions? Is there room to swap the lines from the left drive to right?

 

[bremery]

The right side track moves a little bit. The left side track does not move on it's own, but if you do perform another function at the same time the track will move a little bit. I just picked up the machine a week ago and I am just starting to dig into it. I knew it was a project when I bought it. One thing I forgot to mention is that the pilot controls are weaping fluid up in the cab. I am not sure if this is causing a pressure drop. I am going to do a fluid and filter change as I am not sure what fluids have been added to the machine.

 

[Muffler Bearing]

sounds like quite a project, good luck drag a magnet along the bottom of the hydra tank and see what it picks up.

 

[willie59]

I've never even seen a Scat Trak excavator in my area, much less worked on one. Your describing things I've never even heard of. My first thought would be a problem with a dual chamber hyd pump, but I don't know if it even has a dual chamber pump, and you stated the pump was tested and checked OK. It doesn't make sense that it would be a pilot system pressure problem, else it wouldn't work by operating a function on the opposite joystick. I can't see how it could be a relief problem because you stated that if you get into a single function, it sounds like it's opening a relief, but again, if you operate a function on the other stick the problem function works OK. Does your pump have "load sensing" hoses going to it, or does it sense the load internally at the pump. You stated boom, stick, and bucket are slow working alone. Are they slow in both directions, up/down, in/out, curl in/roll out? Just tryin' to get a little more info because I have no idea what's going on at this point.

 

[OCR]

Hydraulic Problem With Pilot Controls:

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.

This is a total guess, but it almost sounds like somebody might have tried to change the pattern and hooked the pilot hoses up wrong.

Especially when you state that the pilot controls are weeping fluid up in the cab.

Take the boom for example... you try to raise it and it sounds like a relief is opening, which it might be, possibly because the return port is hooked to another lever, and when you activate the other lever, the return port opens and it seems to work.

Again, just a guess, and I don't know if it even works that way, but it sounds like a conflict in the valving some where.


OCR

 

[bremery]

The machine has a triple gear pump, and it does not appear to have load sensing hoses going to it.

The functions that work all the time are the dozer blade, offset boom swing, and house turntable. The turntable is the only thing on this circuit that uses the pilot controls, the others are purely mechanical spools with linkages. I have been trying to figure out why these work all the time. These circuits do not have port or antishock vavles like all of the other circuits, I am not sure if this matters. Just giving some additional information.

I guess its possible the hoses could be wrong going to the pilot control. I will have to double check the routing.

I am waiting to get a hydraulic filter so I can eliminate that, and I will try to get to the in tank filter to clean it. I keep thinking about a clogged filter, but it would not make sense that the dozer blade circuit would work fine and the others would not.

I appreciate everyone's comments so far. I look forward to hearing any further suggestions.

 

[willie59]

The machine has a triple gear pump, and it does not appear to have load sensing hoses going to it.

Are you for real about that? Triple gear pump? Man, I said I haven't worked on one...and I wouldn't have dreamed of that on an excavator, even a small one! If it has gear pumps, there wouldn't be sensor lines to the pumps, but I would just about bet that it's a closed center hyd circuit. With gear pumps, this would require some kind of load sensing valving to dump oil from the positive displacement pumps when oil is not needed, I guess you could call it differential sensing. JLG and Genie uses gear pumps on closed center circuits with these type of sensing valves, but I have no clue what Scat Trak is doing on this excavator. But I'm still curious what's causing your problem.

 

[bremery]

Yes, it is a triple gear pump. Is this a good or bad thing?

I bought a manual for this machine. It is not a factory manual, but more like a translated manual from Italtian to English. The machine is the same as a Libra excavator which I have heard is some sort of mining equipment manufacturer in Italy.

After looking at the hydraulic circuit I have discovered that there is a high power circuit that is engergized by a solenoid. When engergized redirects return flow from from circuit 1 (Which is the dozer blade, swing, and slew) to the other two circuits. This is currently how the machine is running in high power mode. When power is shut off to this circuit flow from circuit 1 goes back to the tank. With the solenoid off the machine barely moves except for the functions on circuit one. They still work all the time. Maybe the second and third segment on the pump are not working?

I am starting to move away from it being a pilot control problem for now. I am wondering if the system is not getting flow from the tank. I am going to drain the hydraulic tank and try to clean the suction filter, and replace the inline filter to see if that helps. All I need is for it to stop raining.

 

[sdcraneman]

Scat track pilot issues

I have a scat track 224s, I'm having simialr issues. I did find out the the machines are still being produce in Italy as Libra units and that the Vermeer factory can and will still get parts for them. I just got the Hyd. schematic for mine today and have begun sorting through it.
Assuming they are a bit the same I have a 3cyl. Kubota coupled to a Nachie variable displacement piston pump with (2) discharge ports, behind that is a a gear pump. The piston pump apparently has an internal circuit that destrokes the pump's swash plate at about the same time the relief pressure is met. I found this by attaching a flow control valve and gauge to the discharge ports one at a time and slowly began closing the valve to see if the pump loaded up and built pressure. (the other end of line I just ran into the tank through the filler cap)
Mine is also plumbed to the control valves in three segments with (2) solenoid operated valves marrying the pumps together for additional flow, this is controled in the right stick with two buttons one on and one off. If you look at the schematic there is a block that has two solenoid valves and an accumulator on it. One of the solenoids gives you high speed travel and the other shuts the pilot oil off if the left armrest is lifted. I'm not there yet but I think the problem is in that valve block. It has two different control pressures one is 35 Bar and the other is 50 Bar. There is a check valve between the accumulator and the 35 bar test port (m-1 on the schematic) I'm not yet certain but somthings fishey there.
Please keep me posted as to your progress and I'll do the same, maybe we can help each other. I can't help but thinking we are not the only two to have had these problems. I'll continue to try to find a mechanic that is familliar these machines as I'm begining to believe this may be a fairly common problem. My machine came from H&E, it was a rental unit. I have limited connections with H&E as the outfit I work for buy's Krupp/Grove AT cranes from them. At the present one of there guy's is trying to find out wich store my machine came from in the hopes and can find out who may have worked on it the past.
Anyway good luck and I hope to hear from you soon.
Best regards,
George

 

[willie59]

Wow, this is getting tangled, one has gear pumps...one has piston!

Gear pumps are neither good nor bad here...just different. Most (in general) excavators use piston pumps and closed center hyd circuits. It would just be not the norm if yours had gear pumps. And if it does, I still think it would be a closed circuit system and have to utilize some form of differential sensing to control pressure output of the pumps. I'm thinking it's a problem of single pump output to a function not working properly, then when you combine flow from multiple pumps via valving, you get a reaction. That's still a vague longshot at this point. And I would be curious that the pumps were, in fact, good. I learned a long time ago when wrenching on something, that if someone says "yeah, I checked that...", I'm going to check it anyway. I want to see it for myself. Is it possible for you to switch the pump output hose around and see if your problems move to other functions? Just a few thoughts.

 

[OCR]

behind that is a a gear pump.

Hello sdcraneman, and bremery,

The gear pump that you refer to, could possibly be the charge pump for the variable displacement piston pump, I know they require some type of charge pump.

That does seem to be a rather unconventional arrangement on bremery's system though. Keep us posted... a learning experience is almost always beneficial to every one.


OCR

 

[willie59]

Hey OCR, I was already typing this on wordpad when I noticed you had posted. Here's a few thoughts I have about the pumps.

sdcraneman, the arrangement you described on your machine is what is more common on excavators. A dual chamber piston pump to supply oil to work equipment. The gear pump that piggybacks off the piston pump provides oil for the pilot circuit. Many of these type of piston pump arrangements have internal load sensing and not sensor lines coming from valves to control pump output. Also, they don't necessarily "destroke about the time the relief pressure is met". Most of these load sensing pumps, whether piston or gear arrangements, are designed to maintain a set pressure on the system. When no functions are being used, this is what we commonly call "standby pressure". It usually ranges from 300 - 500 psi. To keep description simple, let's say 300 psi. The machine is running, your operating no functions, it's a closed center hyd circuit (which is a dead end), and the sensor circuit "destrokes" the pump to maintain 300 on the system. Now, you operate the boom. There is a pressure drop because oil is being demanded. The sensor circuit says "oh shoot, pressure went down!" It "strokes" the swash plate to deliver more oil because it's trying to maintain that 300 psi. But wait a minute, the boom requires more than a meager 300 psi to raise it doesn't it? That's right. That's where "pressure differential" comes in. The sensor circuit is always trying to stay 300 psi above what is demanded. Let's say when you operated the boom, it required 1,000 psi of pressure to operate it. At that point, the sensor circuit will adjust pump to deliver 1,300 psi of pressure. 300 lbs above what is demanded, pressure differential. Gear pump arrangemnents can do this as well, but in a slightly different way since they can't "stroke/destroke". Gear pumps, or positive displacement pumps, produce flow constantly. When no functions are being used, and it's a closed center circuit, that pump is going to produce oil flow. Something's going to blow! So you commonly will have some form of differential sensing valve that dumps oil from the pump back to tank, except for that magic 300 psi. It just holds it there. When you operate a function and oil is demanded, the valve closes the dump line and lets the oil go to the function selected, and again maintains 300 psi more than is demanded, excess is dumped to tank. Well, that's the nuts and bolts of the pumps, now we just gotta figure out which component has decided to be the problem child in this three ring circus.

 

[OCR]

Hydraulic Problem With Pilot Controls:

Man ATCOEQUIP,

That description was way better than you can get from most tech manuals.

Good'un... :thumbsup


OCR

 

[sdcraneman]

Thanks guys,
I thought the gear pump was probably a charge pump also. The stange thing is, it is plumbed into the control valve on The end I believe. The 2 ports on the piston pump are set up to feed the center and the opposite end. I didn't see any plumbing that even feeds charge pressure to the piston pump. I was thinking that maybe it is internally ported?? The gear pump gets it feed oil from internal ports in the piston pump as there is only one feed line 2-1/2" that goes into the piston pump. I will tell you that the tank is high than the pumps by a bunch, lubrication by head pressure??? I wouldn't think so but I'm just not sure and the schematic isn't that detailed.
Thanks again guys, with your help I'm sure we'll figure it out.
Best regards,
sdcraneman

 

[JS580SL]

Craigslist project #???? Least I didnt have to come over with the backhoe this time to unload it......... I knew you couldnt resist buying it, I saw it hiding out back, haha.

 

[willie59]

Man ATCOEQUIP,

That description was way better than you can get from most tech manuals.

Good'un... :thumbsup


OCR

Well, I'm just a High School edjumacated hillbilly from East Tennessee. Sometimes, I have to take that high tech stuff in the manuals and translate it for myself so myself can understand what it said. Other times...I'm of all men most confused!

 

[willie59]

Thanks guys,
I thought the gear pump was probably a charge pump also. The stange thing is, it is plumbed into the control valve on The end I believe. The 2 ports on the piston pump are set up to feed the center and the opposite end. I didn't see any plumbing that even feeds charge pressure to the piston pump. I was thinking that maybe it is internally ported?? The gear pump gets it feed oil from internal ports in the piston pump as there is only one feed line 2-1/2" that goes into the piston pump. I will tell you that the tank is high than the pumps by a bunch, lubrication by head pressure??? I wouldn't think so but I'm just not sure and the schematic isn't that detailed.
Thanks again guys, with your help I'm sure we'll figure it out.
Best regards,
sdcraneman

Yep, sounds like your gear pump is for pilot/control pressure, fairly typical. And the piston pump is fed by the higher tank level as well as most of these systems have about 15 psi of pressure at the hyd tank. You'll probably hear a hiss if you open a fill port on the hyd tank after you've run the machine from this pressure. It also sound like your describing a dual piston pump on your rig. You said your machine "has similar issues", give us a description of the things your machine is doing. At this point of head scratching, any info is useful from either one of you because we are not there tinkering with the machine.

 

[bremery]

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 still flow related, but I am running out of ideas. Someone mentioned pilot filters? Any ideas of where these could be and if they can be troublesome? What about air in the system? Can that cause airlocks? Can it be bleed.

Thanks for everyone's help so far.

 

[willie59]

I sure would like to see the schematics on these machines. I kinda clueless without them.