I recently purchased a used Case 85XT skidsteer. I have a homemade brushcutter that I built and use with my 743B. Yesterday, I hooked up my brushcutter to the 85XT (which by the way, is a bigger machine than my 743B and has about twice the hydraulic flow). The brushcutter spins up fine and seems to have plenty of power but when I try to move the machine forward or backward it seems to take hydraulic flow away from the cutter. It still has enough power to do both but every time you move forward or backward there is a slight surge as the cutter speeds up (when parked) and slows down a little (when moving). Is this normal? My 743B never did this. I there some powerbeyond port that I need to unplug somewhere? You guys have any ideas?
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Well i'm not sure how the hydraulics are designed on the case machines, but on bobcat machines there are seperate pumps for the hydrostatic drive and a seperate pump for the hydraulics. So you will not loose any flow from the hydraulic system if you are driving, you will loose a little power as the engine gets loaded down but this is to be expected. This could be totally normal for your case machine. I'm sure someone else in here will know better.
Yes I know what you mean....the Case has a separate hydraulic pump mounted on the end of the hydrostatic pump just like my Bobcat. This pump is for the lift arms and also the attachments but I think it also serves as the charge pump for the hydrostatic pump if I'm not mistaken. Anyone?
Does the engine Bogg down? Your charge pump is in the hydrostat assembly itself, or should be in it. they are the same basic design as the 743.
No, the engine does not bog down. I spoke with the mechanic at my local Case dealer this morning and he said the same thing you did (that the charge pump was built into the hydrostatic pump). So this means that the hydraulic pumps only load is the brushcutter itself. He seemed to think that since the Case was putting out about 21 gpm and the hydraulic motor on the brushcutter only required about 12 gpm that I might install a flow control on the supply line to the brushcutter to limit the amount of flow to the cutter and free up more fluid for the hydrostatics.
That sounds like a good idea, I'm amazed that you didn't overheat you loader trying to push that much fluid through it. well good luck
I put an inline flow control on the supply side of my brushcutter and after some adjusting it seemed to take out the surging when I move forward and backward. This still doesn't seem like the right solution though....here's why: The Case 85XT has a foot control that activates the aux. hydraulics. When you push the lever down with your foot, it locks in place for continuous flow. Now, at this point the valve is open fully (21 gpm) and if the fluid has nowhere to go, I guess the relief valves open up to let the fluid bypass. When this is happening, the engine is loaded up and you can hear the engine bog down. I would imagine if I let it run like this for long the fluid would overheat wouldn't it? Anyhow, when I open up the flow control to let a small amount of that flow to the cutter (say 10 gpm), what happens to the other 11 gpm left over? Is it backing up and causing the relief valves to open up, hence causing more heat? If what I'm saying is true, what would be the best way to control the amount of flow to the cutter? Thanks so much for your input.
skidsteer.ca
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You either need a larger hyd motor or a flow devider that splits one pump (your loader) into 2 outputs, the unused portion would just bypass to the return line of the brusher and go back to the loader. ( no restriction) If you go with a larger motor you can increase the torque by nearly 100% driving your brush cutter. Unless your flow control has a bypass line to return the excess oil to the machine, it must just be "backing up the oil" by means of restriction. We use flow deviders on wood slashers up here. It splits about 10 gpm off a 40 gpm pump. Regardless of the pressure on ether side, the other always recieves the "set" volume. The 10 gpm runs the bunt board and saw cylinders and the other 30 gpm is used to run a 60" saw. The machine cuts trees (several at a time) into 8' pieces. What happens if you reduce you engine to 1/2 rpm? (then you21 gpm pump would be down to 10.5 in theory) If you have enought power to move around, that may be good enought to. If you put a pressure guage in the system and slowly increase you engine speed, you will see the pressure climb quickly at the point where you hyd motor can no longer flow enough gpm.
I have since purchased a service manual for this machine and I think I now know what is causing the problem. The hydraulic pump also serves as a charge pump for the hydrostatics. When the levers are in neutral, all of the flow is directed to the equipment port (for the loader arms, attachments, etc.). Then when you move the levers forward or backward, a shuttle valve on the drive motors opens up to allow fresh fluid to enter the motor to keep it cool. When this happens there is an initial surge of flow to the motors and this flow is taken away from the equipment port. The manual states this is a 2 gpm loss immediately (and this is on a new machine with no wear). This sudden surge/loss of flow is what is causing the brush cutter to surge. When your cutting brush, you move back and forth alot, and this gets very annoying. It seems that this may just be something inherent to the design of the machine and there's nothing I can do about it. I guess if it was a highflow machine with a separate hydraulic pump just for the attachments then I wouldn't have this problem. I don't know, maybe I can come up with some way to make this work. Right now, I'm at a loss.
The charge pressure is just used to replenish the losses in the hydrostatic pumps and motors, this is only a small loss and you shouldn't notice it in your hydraulic flow, it will be there but will only be a few GPM under full load less if you take it easy. I believe Hi-Flo setups are still the same, they still act as charge pumps but have a higher pumping capacity.
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I take it you have looked into the amount of flow your brushers max is? It does not seem to help to reduce the engine rpm, the brush cutter still surges when you move the machine? I certainly don't notice this with my 773 bobcat, I only get a surge when moving the boom cylinders as the pump fllow is directed there momentarilly. Ken
The brusher requires 12 gpm, I don't know what the max would be. Engine RPM (low or high) does not seem to help. The surge you get while moving the boom cylinders as the flow is directed there momentarily is exactly what is happening to me except when I move the levers forward or back, the flow is momentarily directed to the drive motors for cooling purposes. As I have investigated further, I have found that the hydro motor on the right side gets weak after it heats up for about 20 minutes. I'm thinking I may be having a lot of internal leaking causing the surge to be more than it should be. I've been doing some testing and am just before pulling the drive motor and installing a new seal kit. I hoping this will help both problems.
