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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

Re: testing hydraulic system on Bobcat 610

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07-14-2009 07:46:59

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Not that familiar with that particular model but I do know some Bobcat machines have a valve that needs to be shifted depending on what type of attachment your using. Basically if your running something with a cylinder you shift it one way, but if it uses a motor you shift it the other. I had a buddy with one of their excavators that was set up this way and if the valve got shifted the wrong way it did strange things.

As for testing hydraulics flow and pressure are so entertwined that it would be impossible to properly test without the proper equipment. You say the auger works but stalls so you obviously have some flow but not pressure. In other words flow even at low pressure will make it turn, but you need the pressure to actually make it do any work. That said the proper thing to do would be put a flow meter, with a load valve, in line between the aux ports and check the flow there at no load. Then slowly close the load valve and see if the flow drops as pressure increases. This would tell you exactly what the system is doing be showing both factors.

Not having a flow meter you can still tee into the line and do a "half way" pressure check, you just won"t know the flow rate. To make up a test tool you need high pressure parts of course. Hook everything into the aux port supplying oil in this order. Tee in putting a pressure guage (3000-5000 psi range will probably do) on the tee port then come out the other port with a needle valve that is then connected to the aux return port. To test OPEN the needle valve fully and actuate the aux ports and note the pressure on the guage. Then SLOWLY close down the needle valve and watch the pressure. The pressure should rise and you should be able to hear the oil flow trough the restriction (simulated load) created by the valve. If you close the valve and it rises only so far to a fairely low pressure (say 500-1000 psi) and then just stops even if you close the valve further then that tells you there is a problem. Loading the circuit with a positive load like this you should be able to achieve at least full system pressure (typically 2500-3000 psi on most smaller machines) before anything happens. Now IF that circuit has a relief you should see a steady rise in pressure on the guage, as you shut the valve, until you reach the set pressure of the relief. At that time the pressure will drop off SHARPLY.....however if there is no relief then the pressure will/should continue to rise until something gives and a hose blows, pump damage occurs, etc. IN OTHER WORDS WITH THIS TEST SETUP DO NOT CLOSE THE NEEDLE VALVE COMPLETELY AS DOING SO COULD CAUSE SERIOUS PERSONEL AND/OR EQUIPMENT DAMAGE.

If I was in the field and had to test a machine with no flow meter this is what I would do. In this case it seems like the problem is more with the pressure than the flow so it may do you some good.....then again it may not since it only gives half of the picture but sometimes half is better than none at all. Any more questions please feel free o ask. GOOD LUCK

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07-14-2009 08:21:01

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 Re: testing hydraulic system on Bobcat 610 in reply to NCWayne, 07-14-2009 07:46:59  
That's really helpful and I appreciate your detailed reply. One follow up question for now: why use the needle valve instead of sending fluid to the auger and increasing pressure on it to the stall point? I know the valve would give me better control, but every component I add makes things more expensive. By the way, this is an old machine from when Bobcats were yellow. The main relief is supposed to be at about 1800 psi and the flow rate is supposed to be 11 gpm.
Thanks again.

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07-14-2009 18:25:50

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 Re: testing hydraulic system on Bobcat 610 in reply to Charlie, 07-14-2009 08:21:01  
You had mentioned having some of the fittings, etc so I figured you might have a valve in with the mix....that"s what I get for assuming... You could do a test where you tee in and do what your talking about and just stall the auger and see what the pressure but it"s not going to be a real indication of what/where the problem really is. By that I mean if the problem is internal to the auger and it"s bypassing pressure when it stalls, instead of letting it build enough to turn, then your going to show a low pressure in the system regardless of whether the machine is the problem or not. By the same token if the problem is with the machine then your also going to see a low pressure when the auger stalls.

Basically the only sure way to test the system is to eleminate even the possibility that the auger is the problem because when it"s attached to the machine the test results are going to be basically the same (low pressure) regardless of whether the problem is actually with the machine or something internal with the auger. That"s the best way I know of to explain it, I hope it makes sense.

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07-14-2009 18:30:07

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 Re: testing hydraulic system on Bobcat 610 in reply to NCWayne, 07-14-2009 18:25:50  

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