Negative control pressure

[Ratmotorhead]

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?

 

[heymccall]

On many machines, bucket dump and stick out are one pump functions.
I know nothing about link belts, but my Cats are that way.

 

[Tyler d4c]

I'm 99 percent sure your ok what made you test it in the first place.

 

[uffex]

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

 

[uffex]

This may help

 

[Ratmotorhead]

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.

 

[uffex]

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

 

[funwithfuel]

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?

 

[John C.]

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!

 

[Ratmotorhead]

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.

 

[Ratmotorhead]

also in my Isuzu book it showed 21 psi from lift pump. It shows black smoke when in stall but not a large amount

 

[John C.]

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.

 

[funwithfuel]

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.

 

[Ratmotorhead]

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

 

[funwithfuel]

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

 

[Ratmotorhead]

My guages are teed into each line to top and bottom of regulator ,coming from each end of each control valve

 

[funwithfuel]

Any chance for a pic, having a hard time understanding what you're describing.

 

[John C.]

There is only one return for arm in. That’s to keep the arm from free fall.

 

[LACHAU]

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?

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.

 

[funwithfuel]

That is when ARM-IN. He ask why is one pump working only at ARM-OUT.


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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.