Hi guys, I've got a question about testing the negative control pressure on my excavator. The machine is a 4300c linkbelt,which I have talked about before on this forum. Today I teed into the negative control lines to my regulator,one in each end of my control valves. My pressure is at 590lbs as it should be at full throttle,and as I move my controls to curl bucket and dipper in,it goes to zero as it should to adjust the swashplates plates in the pump. My question is , when I extend the dipper and bucket, the one side hydraulic control valve goes to zero, but the other does not. Does this seem correct ? I would think that both should drop to zero to signal pump just like when curling in. Any thoughts?
On many machines, bucket dump and stick out are one pump functions. I know nothing about link belts, but my Cats are that way.
I'm 99 percent sure your ok what made you test it in the first place.
Good day If your machine is operating normally and there are no faults I would suggest that all is correct you have two sides to the main valve chest for which each pump provides fluid . When raising the boom or operating arm in most machines will use both pumps where as the bucket and swing only use the one pump two pump connection is not possible. When you operate the bucket on its own it has to use a pump and this must show up in the negative control line draining down to allow the pump to begin providing fluid. We have more information on this regulator system if you are interested from me a PM with you Email, if you have a problem with the machine not yet mentioned please come back and we will try to help. Kind regards Uffex
This may help
Thanks for the quick response guys. My machine bogs the motor when using the stick in function ,and I am testing to see if regulator is correct. I understand that two pumps operate during dipper use.when I use the dipper only function for curling in both my guages in my negative control lines will drop to zero, if I use dipper out function only,only one drops to zero, and it stops movement pretty harsh. The other functions seem to work reasonably well. I keep fuel clean and have 22lbs fuel pressure, banjo bolt filter clean,sediment filters,etc . I can bury my 54 inch bucket in my topsoil pile and bucket curl with no prob, but when I combine in a little dipper involving both pumps , bog. I am showing 4550 psi out of both pumps. I am starting to think I am having regulator adjustment issues but wanted to be sure that the neg pressures are correct.
Good day RMH Your description of the measurements you have made are correct there is no fault with the negative line, I do not have a schematic for your machine if you have and can post I will try to help some more, our experience is that hydraulics are not self adjusting but there can be other components that may effect regulation. I understand you are reasonably happy with the engine but for what is worth our experience is that it is the most likely suspect. Servicing the fuel system - checking the turbo & muffler - intercooler and air induction are all elements worth a thorough check. Kind regards Uffex
It sounds as if your pump is not de-stroking. If your second pump is drawing the rpms down it would suggest that the pump is stroked up and there is nowhere for the oil to go but past relief. If you raise your boom to end of travel, how does it behave, the same or do you maintain eng speed and overrun the relief? I ask this because boom up uses 2 pump flow through center passage. It should behave the same if it's a hydraulic issue. What engine do you have, 22psi seems light? Are you seeing black smoke when she falls ? Is this cummins powered or isuzu?
First of all, how many hours do you have on this set of pumps? You have a very common problem in the regulator valves on the pumps. Those old Link-Belts have no control on the NC lines other than on or off. When you operate a function, the pumps go to full stroke and then back off through the regulators on the pump. The regulators work by seeing main pressure and bleeding off that pressure at a regulated rate to increase the output of the pump. What happens over time is that the bleed rate increases with the erosion of the valves which increases the output of the pump and overloads the engine. There are bleed rate screws for each pump and single screw for controlling those situations when both pumps are on at the same time. I worked at a Link-Belt dealer when the CII machines were the most common models. Your issue usually was the indication that the pump didn't have a lot of time left. You can remove and tear down the regulators, clean them up and reinstall them and probably adjust them back to factory spec. You will probably find lots of junk making those little spools sticky inside the bores. All that junk has been going through the pump so be aware that a sudden change in operation of the system means you better shut the machine down quickly. Good Luck!
It has the Isuzu ,when I boom up all the way it goes to relief and does not stall the engine,actually all functions will go to relief and I was able to get relief pressures to spec. The dipper on the other hand will go to relief, only if I pull into it quick and hard. If I slowly pull the dipper back to get it to relief it stalls out motor. I just thought it was odd that my nf pressures went instantly to 0 psi on both hyd valves during retraction but only one went to 0 psi during extension. I am sure it has over 10,000 hrs on the pumps ,but I may have the nc valve in one hyd valve sticking. Still very clean in hyd fluid and return filter to tank was clean when I cut it open earlier this month. It just feels like it can't destroke fast enough in retraction of dipper.
also in my Isuzu book it showed 21 psi from lift pump. It shows black smoke when in stall but not a large amount
You can't tell the cleanliness of hydraulic oil by looking at it, only by analysis. Also the stuff that gets into the regulators happens over time. As I said, the NC valve only turns the pump on or shuts it off when a spool it moved. It plays no part in pump regulation.
Arm in or retract requires more volume than arm out. That's why both pumps stroke in one direction and not the other. You may wanna look at your arm regeneration valve, if it is stuck or sticking, that would have a no reduction signal situation I believe. I don't know what Link-Belt calls it but that's what I'd be looking at. Since your boom up doesn't stall or bog you down.
I guess I am trying to find out if during my testing on dipper out both of my guages should go to 0 psi, maybe it is correct because of less volume on extend. The machine has the feel of dipper in or out fighting each other, if that makes any sense,like it can't return oil back to tank fast enough. You may be on to something funwithfuel, I don't know what linkbelt calls this valve either ,if there is one . I will scan my hyd schematic , but I haven't been able to locate
No , arm out should only have one side of spool dropping off, not both. The same for arm in , the opposite side should drop off. I thought we were talking pump regulator not servo caps
My guages are teed into each line to top and bottom of regulator ,coming from each end of each control valve
Any chance for a pic, having a hard time understanding what you're describing.
There is only one return for arm in. That’s to keep the arm from free fall.
That is when ARM-IN. He ask why is one pump working only at ARM-OUT.
Yeah, but what is the best way to test against this function. I don't think he has a regulator issue, so much as a valve/function issue.
You should check the ARM 1 and ARM 2 spools for what spool donot work.
According to the schematic, the arm 1 and 2 spools both move when either in or out are moved. If the schematic is correct then both NC pressures should drop. The other issue is that the schematic shows the single return in the arm 2 spool and on the arm out function. That isn't how I recall the system was set up on the CII machines but that doesn't matter. In either case whether working that way or not it shouldn't be possible for the pumps to overload the engine. There appears to be a check valve and restriction in the spool for the arm 1 valve and as Lachau states, you should make sure that spool is clear and the check valve is in place.
I appreciate the responses guys. I have pulled the arm spool in the left hyd valve and it was intact and moved smooth,spring good. I will have to check my notes tomorrow on right valve spool, but I believe I did that too during my clean out . I will check again. Another thing which concerns me is , on the regulator is an electric solenoid. This machine has no monitor in it ,or any mode controls. I have the hydraulic safety circuit on an on off switch,works well. I have the free swing circuit on an on off switch, works well. Currently this solnoid on regulator is on 24volt, power on, it has a pin that shoves in, with spring that pushes out. I do not read schematics well enough to know if in is full power or out is limp mode , or vise versa . Could that be part of problem?
Looking at how the schematic shows fluid path on the extend side, that tells me when dipper in is used,fluid must return back to tank thru check, which would make it feel like fluid is deadheading when not getting back to tank making engine bog. That looks like check is in right hand valve body. Am I thinking right? I will get into that tomorrow giving my results. Thank you all for any and all input. Also any info about regulator solenoid,what it does ,or how it's fluid path works would be greatly appreciated
It's not correct!! That solenoid to control the regulator of pump 2. Which to control the option attachment like breaker etc. by increasing or reducing the pressure to PZ2 port on pump 2 regulator
Pleased see attached image.
Thanks Lachau, since my machine has had aux hydraulics removed, should that solenoid be energized or not,according to the schematic?
Today I ran machine for a while with the solenoid on the regulator disconnected. Not really any noticeable change, man ,the motor runs really great. And yes funwithfuel the motor bogs when boomed all the way up, and it won't make it to relief without killing motor. Black smoke when bogging. Is there a rule of thumb setting that heavy equiptment repairman use, or a baseline setup for a regulator setting on these machines? Finding a factory setting from my standpoint is slim and none .
I have a drawing of the CII pump that shows where the adjusting screws are. The C series pumps have the same screws but in different places. If you send me a PM with your email address I can send what I have left from those days.
Well, that's different from what you stated earlier. I thought we had it isolated to the MCV. If boom up does it also, then we're looking at a fault that requires 2 pump flow. Do you have an old pin that you could stall the tracks with? I'd be curious to see if you have identical pressures from left to right. If track pressure is equal, side to side, and neither stalls or bogs the engine, it would still be in the MCV. With the schematic provide, I'd be tracing any common passages between boom and arm circuit.
Hello men, between rainfall today, I ran excavator to test track performance. On right track 4200 psi at full throttle, goes to relief with no stall in forward. In reverse 4000 psi goes to relief no stall. On the left track, 4100psi forward full throttle no stall. In reverse 4100psi, goes to relief no stall.
Were your tracks stalled when testing? If they were, I still have a hard time finding fault with your regulators. More MCV, I think.
I didn’t pin off both tracks at same time but I will tomorrow since I ran out of daylight. When extend dipper goes to relieve no stall. I used 3inch bar to stall tracks.
That's cool, it doesn't have to be at the same time. Just so long as those are stalled track values. Your engine didn't fall off, so I believe your regulators are ok. Your arm function seems to have a little debris in it as it bogged the engine, then it didn't. There's a ball check or orifice with a piece of packing or o-ring somewhere. Unless maybe your line to regulators is obstructed or has a flapper essentially trapping the oil on one side or the other.
The photos show my left hyd valve . It was swapped out because if I was getting this stall issue on retract I couldn’t isolate it bypass in spool. The protruding valve is on the extend dipper side. The center hose is the pilot control, the hose on the end, and hose on right, has never given any pressure ever.
I have had spool out in original hyd valve, it was smooth moving, good spring,even removed return side valve, that protruding one which I don’t have correct name for, it was clean and free moving. With the replacement valve in with the same problems, stall, happening I am thinking issue may be before or after main valve. Hence regulator. I have even capped off lines to dipper cylinder to test if packing was trash but it showed good
I thought about a flapper in the regulator hoses, but they are the solid nylon type to all my pilot areas, could happen though . My hoses at cylinder are new also . For what it is worth I even resealed my swivel in the spring, just to eliminate that possibility, it needed done, glad I did it.
Hey funwithfuel, is the black valve in my photos the arm regeneration valve you mentioned? It is in the extend line side of dipper spool, should this valve have any pressure to it during dipper retract, or pilot pressure,to help oil back to tank during dipper retract? Thank to all for the help and suggestions.
I don't honestly know. I have very little experience with Link-Belt excavators. I have a grasp of basic hydraulics, and what I have personally encountered through experience. That's why I was so relieved that Lachau and JohnC were sharing their insite.
This may help. I’m trying to find some restriction somewhere on return on dipper extend and boom down, back to tank
Today I tried to look for any restrictions, and found a filter screen in the schematic in the regulator, and it was clean. It shows 3 in quantity but there is only one I found , all inlets checked.
what is the mcv valve that funwithfuel mentioned?
MCV = main control valve.
Ok thanks I replaced the left hand mcv this spring,thinking a spool could be allowing bypass. Seems same problem exists. I am going to increase fuel pressure to 40 psi to see if any change during stall.
Worked on excavator a little this evening. I increased the fuel pressure to 60 lbs instead of 21lbs. Wow what an improvement. My Isuzu engine book showed 21, how could I tell if this is correct ? I shimmed spring at return to tank valve, not sure of tech name for it ,and ran return hose to bucket. I still had a small amount coming out of hose,so I know it wasn't completely blocked off. I ran machine at full throttle and put dipper into relief, no stall. Boomed up all the way to relief and it did start to stall, but only after holding in relief for a near 15 seconds. Didn't dig with it tonight, but I am impressed. These improvements only come from the tremendous input from this site. Thanks guys!