Bobcat 763 Help

[Hilbilly]

I've been in the process of converting my 3pth snow blower to hydraulic so I can run it on the Bobcat. I got the pump mounted on the blower with direct drive and put the blower in the SS snow bucket to see if it would work. It did but not well. So I did some checking and I think I have a pressure relief valve issue with the SS. I put a hose between the auxiliary out and in ports with a pressure gauge on the line. I'm getting about 600 psi in that line at full throttle. According to the service manual it should be 3000 psi. Also according the service manual the Main Relieve valve should be adjusted to increase the pressure. I found a picture showing the location of the main relief valve and tried adjusting it but there is no change. The relief valve has a cap over the adjusting screw and a locking nut. I have removed the cap, loosened the locking nut and used an Allen key to turn the adjuster in. So far I have got a total of 5 partial turns (maybe 1/8th turn each) clockwise and there has been no change. Am I doing something wrong or is the valve defective?

 

[oldnslo]

By connecting the aux ports you have created a flow path so you will not read system pressure. Just plug you gauge into the aux pressure port and activate that function. You will now read full system pressure.

FYI: If the blower ran to slow that is flow issue not a pressure issue. In hydraulics flow equals speed and pressure is force or torque.

 

[Hilbilly]

Thanks oldnslo.

I got it working and have a cross over relief valve between the SS and the blower motor. The relief is set at 2900 psi. The motor is rated for max continuous pressure of 2973. At full throttle the blower works but does not throw the snow very far and bogs down quite easily. I think the problem a lack of flow, like you say. I thought about putting sprockets on the motor and the blower gear box to increase the blower fan speed but that would reduce the torque and then I'm back to the blower bogging down. I talked to the hyd motor dealer and asked about using a larger displacement motor but they are rated to run at even slower speeds. I guess I'm stuck with this setup, unless you have any ideas to improve on it.

 

[oldnslo]

What make & model of motor did you use? Did it have a flow Vs RPM chart?

Also be nice if the chart included torque vs differential pressure

What size hose did you have on the loop when you where initially trying to check pressure. The 600 PSI is all back pressure and reduces the amount of power to run the motor.

 

[Xfaxman]

This is how I setup my pressure gauge:

I can put it in line to see if I am going too fast in thick grass or heavy brush:

The low-flow brush hog uses 3/4" hose.


.

 

[Hilbilly]

What make & model of motor did you use? Did it have a flow Vs RPM chart?

Also be nice if the chart included torque vs differential pressure

What size hose did you have on the loop when you where initially trying to check pressure. The 600 PSI is all back pressure and reduces the amount of power to run the motor.

The pump is a house brand from Princess Auto and here is a copy of the table in the owners manual.

I used 1/2" hose. Which I think is too small but the steel lines to the Bobcat aux connections are only 1/2".

This is how I setup my pressure gauge:

View attachment 541819 View attachment 541821


I can put it in line to see if I am going too fast in thick grass or heavy brush:

View attachment 541820



The low-flow brush hog uses 3/4" hose.


.

View attachment motor.pdf

I like that setup and thanks for the tip on the 3/4" lines. I think that might be part of the problem but I think there is a bigger one producing that 600 psi back pressure.

 

[mikester]

You should consider picking up one of those cheap laser tachs at PA they were on sale again recently for like $20. Disconnect the motor from the blower and confirm your hydraulic motor RPM vs the skidsteer engine RPM. I'd suspect you are only getting something like 12-13 GPM on your flow which is keeping your PTO RPM's down.

On my setup I used the 5.9cu.in motor and my tractor was pushing at best 12 GPM and 2500 psi but I was able to throw the lighter snow a good 40 feet. Then again maybe your snowblower gearbox might have a lower gear ratio to the secondary impeller which is why it doesn't throw as far. Heavy wet snow meant I had to go slower and it didn't throw as far.

 

[Hilbilly]

Good timing; I picked up one of those laser tach's yesterday when I was in the City.

This blower has never thrown snow very far. The tractor has a claimed 38 hp pto and running it at pto speed I might get 25' out of it when the snow isn't heavy. The smaller motor might be an idea. The tech at PA even suggested I bring this one back if I wanted to try different one. Right now I think the bigger concern is to resolve the heat and back pressure issue. These could kill the motor and the SS. By the way did you hook up the case drain on your motor. I did not.

edit, Xfaxman; do you think the back pressure could be caused by plugged case drain filters. I've never checked them in the 200 hours or so that I have on the machine. It appears the hydraulic fluid needs to be drained from the system to check them. Is that right?

 

[Xfaxman]

--------------------------

edit, Xfaxman; do you think the back pressure could be caused by plugged case drain filters. I've never checked them in the 200 hours or so that I have on the machine. It appears the hydraulic fluid needs to be drained from the system to check them. Is that right?

No, they were not in the the loop with your pressure gauge.

It appears the hydraulic fluid needs to be drained from the system to check them. Is that right?

No experience with case drain filters, so can't answer that question.

 

[mikester]

Good timing; I picked up one of those laser tach's yesterday when I was in the City.

This blower has never thrown snow very far. The tractor has a claimed 38 hp pto and running it at pto speed I might get 25' out of it when the snow isn't heavy. The smaller motor might be an idea. The tech at PA even suggested I bring this one back if I wanted to try different one. Right now I think the bigger concern is to resolve the heat and back pressure issue. These could kill the motor and the SS. By the way did you hook up the case drain on your motor. I did not.

edit, Xfaxman; do you think the back pressure could be caused by plugged case drain filters. I've never checked them in the 200 hours or so that I have on the machine. It appears the hydraulic fluid needs to be drained from the system to check them. Is that right?

If it never threw snow very far then its the gearbox and its out of your control. I'm curious to see what your motor RPM is with your existing setup

 

[Xfaxman]

I went out and took pictures with the brush hog parked on concrete, no resistance to the blades, showed 500 pounds to spin the blades at max RPM and 175 pounds on the return hose.

Cutting heavy grass, moving fast the pressure will go up to 1,000 or 1500. Too fast in brush will show 2500 and you can hear the pressure relief in the brush hog open.

 

[Hilbilly]

I went out and took pictures with the brush hog parked on concrete, no resistance to the blades, showed 500 pounds to spin the blades at max RPM and 175 pounds on the return hose.

View attachment 541969 View attachment 541970


Cutting heavy grass, moving fast the pressure will go up to 1,000 or 1500. Too fast in brush will show 2500 and you can hear the pressure relief in the brush hog open.

Thanks for doing that. It would appear I have a problem if I get 600 psi with nothing hooked up. I called the Bobcat dealer 2 days ago and asked if this was normal and if not where I should start looking. He said he would call back shortly. I don't expect to hear from him now, unless his idea of shortly is a week or so,lol.

I used the blower again and at first it seemed fine. After about 15 minutes of use the remote lines were only warm to the touch. But another 15 minutes and they were hot. I got out and checked the oil cooler lines. They were warm but not hot. The input line was warmer than the outlet. The remote lines cooled quickly after turning the remotes off but they also heated back up quickly. I think I'll call the dealer again tomorrow and see if they will help or not. I'm just looking for an honest answer. If they are not willing to help I totally understand.

I did take an RPM reading on the blower input shaft with the SS running at full throttle and the blower running but no load. It was 523 RPM. By the way, after using it more today I am satisfied with the performance. It's not a lot worse than on the tractor but I can now drive forwards. Waaaaaaaay better. Just have to sort out the heat and back pressure issue.

 

[oldnslo]

Back pressure things to check.

What size and style are the quick disconnects. These can be a source of pressure drop.

Line or tubing size on the SS? Not sure but would like to think bobcat sized these for continuous use.

Any kinks or pinched points in the return line or hoses.

Can you install the gauge and take pressure readings from idle to full throttle. Curious to see if the rise is linear or does it suddenly climb.

 

[Hilbilly]

Back pressure things to check.

What size and style are the quick disconnects. These can be a source of pressure drop.

Line or tubing size on the SS? Not sure but would like to think bobcat sized these for continuous use.

Any kinks or pinched points in the return line or hoses.

Can you install the gauge and take pressure readings from idle to full throttle. Curious to see if the rise is linear or does it suddenly climb.

The QC's are 1/2" Pioneer style and the hoses are 1/2". The steel tubes on the SS are 1/2" and one of them has a bit of a kink just before the remote connection point.

I recall the pressure increase was linear from idle to full throttle. Idle was about 50 psi and I could watch the pressure increase steadily as I increased throttle. Definitely not a sudden increase. Full throttle pressure of 600 psi, with nothing attached. Just a loop from the remote out to the remote in, using 1/2" hose. There is a total of 12' of 1/2 hose. I could easily reduce this length but I doubt that length alone would produce that kind of pressure lose. From the graph I got from PA 1/2" hose at 15 gpm would produce 3 psi pressure lose per foot of those. Total of 36 psi at full throttle.

 

[oldnslo]

According to my reference catalog 1/2 OD tube requires a wall thickness of .049 to run at 2700 PSI . This reduces the ID to .400 @ 12 GPM this 30 feet/ sec and approx 8 PSI / foot.

 

[Hilbilly]

According to my reference catalog 1/2 OD tube requires a wall thickness of .049 to run at 2700 PSI . This reduces the ID to .400 @ 12 GPM this 30 feet/ sec and approx 8 PSI / foot.

I just mic'd the steel lines on the SS and they are 5/8" OD, so I'm thinking that would be 1/2" ID. There is about 5' of this on the output and return lines, then it connects to 3/4" flexible hose that runs to the back of the SS.

I called the dealer and I'm waiting for a reply. There used to be an awesome parts guy working there that would bend over backwards to help with things like this. He would even get one of the mechanics to come to the phone to answer questions. Unfortunately he left and the new guy is one of those very abrupt kind, that gives me the feeling I am interfering with his life and wants me to go away.

 

[Hilbilly]

I gave up on the local Bobcat dealer and phoned one of their other offices. Big difference. The guy in their service department was very helpful and willing to help. I descrobed my situation to him and he said it was normal for the pressure to build up like that and or the lines to get hot when the machine is working hard. I still think the pressure build up is high but that is just a feeling, not based on real information. I also asked about max oil temps and he said he thought it was around 170 F but would have to check to make sure. I didn't want to bother him any more than necessary and said I would google that. I thanked him for being so helpful.

I'm going to take an IR thermometer with me the next time I use the blower to see what temps the lines get up to. That may not happen again this year though. The temps have warmed up today and we are getting some rain. Next comes the mud season :thumbdown: and it's going to be a nasty one this year because of all the snow that has accumulated.

 

[oldnslo]

Hillbilly
I agree that 600 PSI seems very high but without moving your pressure gauge around it will be hard to pinpoint the source. You would have to install the gauge at various points in the return line to see if any one item shows excessive loss.

Possibly run the unit for a few minutes and see if one point is generating heat or getting hot compared to line upstream. Heat is power (pressure) loss.

I presume your auxiliary function can be used to operate a grapple so the flow has to go through a directional valve. Is this correct?

If yes this adds more plumbing and line length & pressure loss.

Agree that 170 - 180 degrees F in the summer would be acceptable but not in the winter

70 degrees over ambient should be about the max temperature differential and preferably less.

 

[Hilbilly]

oldnslo,

I'll look for hot spots tomorrow and thanks for that.

You are correct about operating a grapple. There is a toggle switch on the handle to open or close the grapple and on the backside of the control handle is a switch to send flow to the remotes continuously. So I guess there must be a directional valve.

I ran the blower today until the lines got hot and I took a temp reading with the IR therm. It read 92 F and the ambient temp was about 32 F. So I guess that is normal. I sure don't like running the SS at full throttle though. I think that is going to kill the poor old thing. I'm considering going to a smaller motor so I can run the SS at a slower speed to get the 540 rpm to the blower. Either that or I could mount the motor differently and use sprockets to up the speed.

 

[oldnslo]

Hillbilly
I would check with PA to see if they have any information on bearing loading for you existing motor. I suspect it would have side load capabilities so that you could then use sprockets to increase the speed and still have the option of greater torque.