Komatsu PC-120-6 61000+ SN. At cold start up relief (Or at least pressure is good) around 5000PSI, After warm up pressures start to decline, eventually to about 3400PSI. Stage 2 relief (Swing brake, heavy lift. travel) does not create any more pressure hot or cold. I have tested all pressures in manual, (control pres, LS, PPC, PC etc etc) Even over adjusting these one way or the other trying to get some type of variance in main pressure to no avail. When testing LS pressure differential pressure it is about 300psi differential as it should be, however during the test(see attachment) Instead of getting Pump Pres= 1150 PSI and servo inlet =640 psi I am getting about 2300Psi pump and 2000 Psi for servo inlet. I cant make any sense out of that or if it even relates to low press. There is not a spec for case drain from the pump as in most other machines, however I checked it and in about 10 seconds got about a gallon of oil from case drain and that is just starting machine, I didnt even get to the point of putting the pump under load. So either this pump is bypassing pretty bad or that much case drain is normal for this pump for reasons I am not failure with like some control valve returning through same port on pump IDK. Any help would be greatly appreciated! Thanks
First, you try adjusting the LS Valve . Your testing differential pressure is 2000 PSI/2300 PSI = 4/5. That means it's not within standard value!!
I so you tried to adjust your main relief and no difference, where is your pressure set at on your secondary, when that pressure is lower, you can adjust your main relief all you want and nothing will happen. Your LS pressure, I would adjust after you figure out your first problem, LS you will only notice in your controls, for finer working.
Have you checked and adjusted the safety-suction valve ? Please note that: if the safety-suction valve set lower than the main relief valve, the two-stage relief valve will not affect.
How would it not effect it?
If my second stage is set lower, I would not beable to reach or adjust my main relief, with main relief I would only be able to reach my pressure what the secondary is set at.
The middle picture is you secondary with the counter nuts and the third pic, is your main relief with your screw, written wrong on the bottom from thevsketch
The Dash 6 line is closed center load sensing. The reliefs only react when an outside force suddenly causes a spike in pressure. A properly adjusted pump will never reach the main relief setting. The pump is supposed to destroke and hold its maximum pressure will little flow. Three hundred PSI is what I have usually seen when troubleshooting these pumps. I know what the book says but also know what I have seen and can say that probably isn't your problem. The PC valve cartridge is to the left of the LS valve cartridge in the pump and it has the acorn nut attached. I've uploaded the page in the book that describes how to adjust that valve. I have had issue with that valve in the past. When it gets worn or the oil is dirty, the parts inside the valve get stuck. You can remove the cartridge and take it apart to clean it but make sure you mark or write down somewhere where the adjustments are. It is easy to adjust, just a pain to mess with that acorn nut.
Ex: Safety-suction valve set at 30 MPa, even when you press the 2-stage button, the pressure is still there, it cannot be increased, it means 2 stage relief valve no longer affect. As I noted that, 2 stage relief valve has PX line = from 2 stage solenoid valve
Please note that cross sectional A-A is Safety-suction valve and cross sectional B-B is Main relief valve.
THANK YOU! all that replied. As far as LS diff pressure I under stand the 3/5 part however if the pressures were as stated in manual (Pump Pres= 1150 PSI and servo inlet =640) Im getting 2300/2000 ish. If i try to adjust LS up, both raise about equally (2800/2500 etc) if I lower LS they will go down and become close to equal around 1500PSI and that is with LS screwed way out. My main point is, it is way higher than the manual says as far as PSI and I can not get 3/5 of differential pressure. weather or not this is an issue IDK. Does anyone have any case drain experience with this pump?
OK, I must confess to being confused by these 3 pages in the manual(see attached) "Testing and adjusting LS valve output pressure" (page1) This test I am getting 2600/1500 PSI listed in table one as 1130/638 is what it should be. However it gives no means or instructions to adjust this pressure. Then moves to Page 2 table 2 to (differential pressure) That is where I am getting the 300 psi differential. I was combineing thes two tests as one or a different view of the same test. Test 2 gives no spec for actual pressure only differential, so I guess it is passing test 2 but test 1 has the correct 3/5 difference however the pressures are way to high. Regardless high pressure is still to low.
Did you read my post? The PC valve in my experience has always been where the problems were at. LS pressure only has to be different and the pump will work to maintain that difference.
John C Yes I did thank you. I am going to remove and inspect PC valve tomorrow. I was just trying to get a better understanding of those adjustments.
Your opinion makes a lot of sense, John. I also think in your opinion, but I want to explain to him about LS pressure first. Please note that: " LS VALVE OUTPUT PRESSURE (SERVO PISTON INPUT PRESSURE) and LS DIFFERENTIAL PRESSURE " are TWO different PRESSURE TYPES.
OK NOW I understand LS valve out is NOT LS. Stupid me. I still do not understand why it is so much higher than the chart. That being said. Removed cleaned and inspected PC valve and safety valve, both clean and good, the safety valve has a internal O-ring or seal that was pretty flat, but would have to get one Monday if that may be an issue-(not sure if its just spring press or spring plus hyd pressure setting the safety) ran in the safety valve adjustment in and same results. Under no load I have quit a bit of oil returning from the cooler, under full load I have a LOT of oil returning from the cooler which seems to me that it is bypassing somewhere in the main control valve. The main relief has a separate hose back to the tank and if I spike the hydraulics I get a small spurt out of which seems normal......
Disregard last sentence, is cooler bypass return not main relief return.
So the way I am seeing it is I dont believe it is a pump or pump control issue. If I dead head any of the cylinders (including track motors) If I have x gallons a min going through main control valve and returning to tank it must be bypassing= main relief, suction safety or unloading valve. I understand it could be bypassing through cylinder or travel motors etc but not likely all of them. All circuits have the save pressure. I dont visually see anything wrong with relief or safety except maybe the o-ring being flat in safety. I am goin to pull and inspect unloading valve Monday. Any thoughts? Any responses are greatly appreciated. Thank you.
If you are sure it isn't the pump or the PC valve, your next step is to remove the compensators in the main control valve. How many hours do you have on this machine and how many hours do you have on the hydraulic oil that is currently in the machine?
I am not sure its not the pump or PC valve, I can only share my findings. On other machines I have worked on they typically give you case drain specs which shows the condition of pumps/motors etc. No such spec for this machine, however this pump has a lot of case drain. Maybe normal for this pump if the LS or PC or something is also returning through case drain. But to contradict that finding I have a lot of oil returning from main cont valve under full load which should be minimal say if pump is bypassing internally and pumping 1/2 it oil through case drain. Pressure or flow has to be going somewhere. High flow bypass through pump(case drain)= low output from pump cant equal low pressure/high bypass somewhere else. If you have low pressure/low or no return at valve then it could be the pump. My point is that when I dead head a cyl and max out the pump, if it was the pump(or pump destroking) it could not still have a ton of return going back to tank because it would be using most of its flow trying to build pressure(all ports being closed in valve) Although I do not like the case drain, at this point I am ignoring it based on that I still have a ton of flow even under full load.
Sry, unknown on the oil. looks and smells good, filters and tank spotless. New display=Unknown machine hrs
Usually, The manufacturers just give you case drain specs which shows the condition of motors (travel motor, swing motor), not for pump!! The reason why I will talk later. Smart opinion. Do you have a flow meter ?? Can you measure exactly how many GPM (or liters/minute) the hydraulic oil returns to the tank from the main control valve in full load condition (stroke end of cylinder)??
Let us now follow up the "case drain" flow measurement experiment to assess the health of the pumps. Since the forum only allows 4 pictures to be uploaded at a time, I have to separate my post.
Video clip here:
That is a great video! I recommend viewing by anyone who ends up working on any type of hydraulic piston pump. Komatsu on their larger excavators actually puts a centrifugal pump in the center section between the front and rear pumps or in the suction line into the pump to ensure that you don't get vacuum in the cavities that contain the piston and barrel assemblies. Vacuum problems manifest by pulling the piston feet off the swash plate and having subsequent damage on the swash plate or in the case of brass slipper feet, destroying them. Contaminated hydraulic oil shows as damage on the seal plate, exactly like the gentleman in the video shows.
Thank you LACHAU for all the posts. However that is the same as what I was saying, or trying to say anyway. The video is awesome but only covers "Low case drain= good pump" I was saying that I had a lot of case drain and was questioning the pump. Lots of case drain COULD mean pump issue, but I was even ignoring that result as I still had plenty of flow from the pump. and I would never use case drain alone to determine anything. I do have a flow meter but do not have fittings to fit this machine. However I am test running the machine with filter/cover removed and can see gallons a minute coming through return with a dead head cylinder. I will guess 5-8 gallons a minute(solid stream about 3/4 to 1in) Much more flow or at least force in return when trying to build pressure with dead head cyl. Inlet housing of main valve and return oil is heating up pretty quick. Upon further testing I do not believe safety valve is bypassing but think its going through main relief but do not see anything wrong with it. I am not certain of that of course, almost $500 at Komatsu and not in stock anywhere! Have not tried aftermarket yet. Has anyone had a main relief bad that did nt have anything obvious wrong with it?
You still aren't listening. You can't get to a relief valve setting with the pump basically in destroke condition. Five to eight gallons a minute is when you get when the pump is in minimum flow. Did you try to adjust the PC valve? Have you checked any of the compensators?
I dont think you guys are listening lol. What have I not listened to besides not pulling compensators yet? On a closed center valve how can you have 8 GPM flowing through main valve and going back to tank under full load?? (This was just a educated guess) It has to be going through somewhere. If a cylinder or a motor is working they will return whatever oil they are using back to tank, but if nothing is moving where is it coming from? I have 2200-2500PSI at the servo piston, the pump is not at minimum flow unless the swash plate is mechanically stuck or the pump is bypassing internally, Yes I have adjusted, removed inspected and readjusted the PC valve. I have not removed and inspected the compensators. Can one of those cause problems across all circuits? I am not at all trying to be argumentative. If I am not understanding something i want to know what that is.
The pump is at minimum flow because it is load sensing. The compensators are all connected together and the load sensing comes from each of them back to the pump.
Dear All, I agree with "John C" about PC valve. First of all, we should check and adjust PC valve properly. As the figure below shows, the P-Q curve of the main pump is dependent on adjustment. If PC valve too loose, the flow of pump will too low===> then pressure can not reach standard value!! In another way of thinking, we should carefully check the unloading valve. This valve have to close tightly also.
Thank you guys for all your help! Love the colored diagrams! Much easier to follow than ye old B/W repair manual. I did figure it out and did not want to be one of those guys that start a thread with a problem and never post the fix. I did have to pull off of it for other projects, and then was out of town bla bla bla life goes on. It ended up being the main relief valve. I made a plug to block of the old main relief and installed it and worked as it should, ordered a new one, installed it and good to go.
Hi bro, I'm junior excavator mechanic.I testing and adjusting LS pressure 300 psi and main pump pressure 300 psi when engine is slow.When engine full load main pump pressure 1800psi and LS pressure 1800 psi All attachment are working but it's doesn't attachment are too slow.Trave is no working.When LS EPC scoket take travel is working but slow.
Please help me bro.Thank you so much all members.
Hello @LACHAU ! What do you mean by 3/5 of pressure? 3/5 of main pressure? Ex i got a pressure of 5000psi therefore LS pressure must be 3/5 of 5000 = 3000psi LS Pressure? Thank you
That means PUMP pressure = 5000 psi (this is the pressure of large area of servo piston) and "SERVO INLET PORT PRESSURE" (this is the pressure of small area of servo piston) = 3000 psi.
Please note that: they are not PC & LS ports. They are PC "DELIVERY PRESSURE" (PC output pressure port) and LS "DELIVERY PRESSURE" LS output pressure port). Please see attached images below.
Still confused why PLUGS 3 and 4 in first picture states that its LS VALVE DELIVERY PRESSURE and in the 2nd picture the same plug 3 and 4 states that its PC VALVE DELIVERY PRESSURE. How much pressure standard should i get in PLUGS 3 and 4? Is it the one says 3/5 or around 3000psi? Thanks @LACHAU .