rexroth a8vo107 for excavator CAT320B

[stevenkn]

hi all,
My name is steven and I just started to learn about hydraulics. so please pardon for my lack of knowledge and if sometimes I ask a stupid question. so here is my hydraulic problem .I have a Caterpillar 320B excavator that whenever there is an arm movement, the engine got pulled down and a black smoke coming out from the exhaust. the track movement is good but the other movement are quite slow(probably only 60 persen of speed compared to a normal one). my questions are:
1. Is the arm problem pulling down the machine could be caused by a wrong setting of the torque limiter, pressure limiting control or the load sensing? if not, what other probable problems could have caused it? The engine is in a good shape so I suspect a faulty component or setting at the hydraulic circuit is the problem.
2. Can anyone tell me or help me with a link on how to set the torque limiter, load sensing and pressure limit on this pump? I tried to download the manual from rexroth website but I only found 2 pdf files and they only showed what each port is for and the specs of the pump. but no instruction for the setting.(I attached an actual picture of the pump)
3. Is there a book or an online course which i can learn from for setting a mobile hydraulic equipment? especially for excavators and wheel loaders.
4. Can anyone recommend me a good place to buy a flowmeter online? In my country, all hydraulic mechanics(for the mobile heavy equipment) do not use a flow meter and probably 90 persent do not use a pressure gauge so its really hard for me to buy a flowmeter here.

I really appreciate any help. Thanks in advance

steven kn

[Doug Hanson]

The torque limiters don't usually go out of adjustment, and when they do, they don't usually pull down the engine. Sometimes the small spools wear in the bore preventing the pumps from destroking as they should.

The first thing you need to do is determine whether the problem is a hydraulic problem, or an engine problem (fuel or air).

Where the charge air comes out of your turbo, there is a short hose to an elbow that bolts to the intake manifold. In that elbow there should be a pipe plug. Pull out that plug and install a 0 - 40 psi guage. When you work your functions and the engine starts to pull down, you should have 18 - 24 lbs of turbo boost there. If not then you have an engine issue and your hydraulics may be fine. Check with your cat dealer on what the boost pressure should be but I think it will be in the range of 18 to 24.

You will probably also notice the engine pulling down if you stall out the boom up function, as this also uses both pumps.

As far as a manual for adjusting the pumps, you need the Cat manual.
If the torque limiters are out of adjustment, a digital flow meter and read out that can record pressure vs flow as a chart is invaluable.

[stevenkn]

Thx for the reply doug,
Do you familiar with this pump? because I have no idea how to adjust the torque limiter, the load sensing setting and the pressure limit setting? any book that I got from CAT dealer is only one book, and its more of a sparepart catalogue than a manual. When I called the dealer, they insisted for their mechanic to come to fix the problem which beats the purpose of me wanting to learn. btw, do you have any reference on a course online or a book or maybe just a website that teaches about mobile hydraulic system(excavators and wheel loaders). especially for adjusting, setting and troubleshooting(i found one link http://www.carldyke.com/courses/load-se ... leshooting but they dont offer it online). Im really frustrated with the mechanics that previously fixed my machines. It seems like they dont even know what the problem is and they keep on guessing and each time I bought or fixed the parts that they said where the problem were, the machine still runs the same. So they will try to "analyze"(more guessing than analyzing to me) the machine again.

[Doug Hanson]

So what is your maximum boost pressure from the turbo when loaded?
Has anyone tampered with the pump regulators?
They arn't load sensing pumps, kind of the opposite. They use negative control pressure signal to destroke the pumps in neutral. The higher the pilot signal the smaller the displacement. The lower the signal, the larger the displacement.
The torque limiter is hard to adjust if the adjustments have been tampered with. You need to plot pressure versus flow while loading each pump, figure out an ideal power curve, make adjustments to get the best results and then try to match both pumps. If they havn't been tampered with you can back the adjustment off a small amount on each pump, but make sure you back both pumps off equally.
Equipment like this makes the job easier, this is the low end Hydac unit: If you have the cat service manual, you can get a fairly accurate idea of where they should be at with the charts they provide.
If your cat dealer won't sell you a manual, look for one on ebay.
I don't know of any courses that are worth taking. Cat has training courses for their dealer mechanics but like to keep that information secret.

[Sergiy]

This pump looks like A8VO107LA1KH1 model. Did you measure the power override pilot pressure?
Does the machine do the same at low engine speeds? I am not familiar with the excavator, but I do know
that the torque limiter threshold on these pumps is decreased by the pilot pressure (the connection in the middle).
The pilot signal should come from some kind of an electric valve (most probably proportional), if it were to have
an offset value, and now is malfunctioning, your
problem might be related to this pilot circuit.

Anyhow - it's just an idea....

[stevenkn]

problem solved. There was some broken parts at controller ,its been replaced and the machine functioned normally right now. Thanks for all help guys. I learned a lot from you guys. Thx again

[hystat]

If the NFC regulators are breaking, look to the attachment circuit. If you have a solenoid operating the ATT spool, the sudden jolt of NFC pressure when the attachment is turned OFF (att spool centers too fast - huge whack of flow down the open center to the NFC orifices) can break parts.
Putting shockless valves in the pilot lines to the attachment spool makes the centering of the att spool more gradual and saves the controllers.