Bobcat 763 C Changing flow rate

[Bobcat_Ed]

Hi all, is there any one out there that knows if the speed of my hydraulic can be slow down on this 763, I am using a snow plow attachment and the speed the plow is moving way to fast, I tried running it on the backhoe hyd and on my aux hyd and the both appear to run at the same speed. it looks like on the newer machines there is a switch on the controls that address this problem. Thanks, Ed

 

[TriHonu]

On the older models the valve for the auxiliary hydraulics is either on or off. The newer models use a proportional valve that allows the operator to control the flow rate from the same switch on the right handle.
Those of us with the older models, just add a flow restrictor in one of the lines on the snow plow. Flow restrictors are a fitting with a small orfice drilled through. It works just like you pinch off a garden hose. The excess flow gets directed through the High Pressure Relief valve and returns to the tank.
The orfice can be drilled out to the size you want. Just make sure you debur and clean all the chips before you reinstall.
The other option is to add a Hydraulic Needle Valve in one of the lines on the snow plow. You can then adjust it to the speed you want. A Needle valve is much more expensive, flow restrictor should be less than $10.
Flow restrictors are only used in circuits with intermittent operation. Continuous operation will cause excessive oil heating.
For my plow, I used 1/4" lines going to the cylinders. This restricted the flow enough for me to control the plow, especially when the oil is cold.

 

[Bobcat_Ed]

On the older models the valve for the auxiliary hydraulics is either on or off. The newer models use a proportional valve that allows the operator to control the flow rate from the same switch on the right handle.
Those of us with the older models, just add a flow restrictor in one of the lines on the snow plow. Flow restrictors are a fitting with a small orfice drilled through. It works just like you pinch off a garden hose. The excess flow gets directed through the High Pressure Relief valve and returns to the tank.
The orfice can be drilled out to the size you want. Just make sure you debur and clean all the chips before you reinstall.
The other option is to add a Hydraulic Needle Valve in one of the lines on the snow plow. You can then adjust it to the speed you want. A Needle valve is much more expensive, flow restrictor should be less than $10.
Flow restrictors are only used in circuits with intermittent operation. Continuous operation will cause excessive oil heating.
For my plow, I used 1/4" lines going to the cylinders. This restricted the flow enough for me to control the plow, especially when the oil is cold.

TriHonu, thanks for all your help! I have one other question on the backhoe side there is a third quick coupling I believe it to be a overflow return line is this ever used in my situation? Thanks, Ed

 

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TriHonu, thanks for all your help! I have one other question on the backhoe side there is a third quick coupling I believe it to be a overflow return line is this ever used in my situation? Thanks, Ed

i would put in a check valve as well so if you hit a curb or something it doesn't put all that pressure back into the machine.

 

[jerry]

i would put in a check valve as well so if you hit a curb or something it doesn't put all that pressure back into the machine.

Check valve would not help since the aux valve is closed after angling the plow. It would have to be a two way relief of some sort between the two angle cylinders. Since the aux valve is closed the most damage you could do is blow a hose but there may be a set-up for this out there.

 

[Bobcat_Ed]

Check valve would not help since the aux valve is closed after angling the plow. It would have to be a two way relief of some sort between the two angle cylinders. Since the aux valve is closed the most damage you could do is blow a hose but there may be a set-up for this out there.

Thank guys for all your help, I purchased 2 restrictors from bobcat today for $9ea installed them and what a difference. This is my first post and found this group to be very helpful. thanks again -Ed

 

[TriHonu]

Thank guys for all your help, I purchased 2 restrictors from bobcat today for $9ea installed them and what a difference. This is my first post and found this group to be very helpful. thanks again -Ed

Quote: Bobcat_Ed - 'I have one other question on the backhoe side there is a third quick coupling I believe it to be a overflow return line is this ever used in my situation? Thanks, Ed'

I have never seen a skid steer backhoe attachment with a 3d line.
Normally a third line is a case drain line. Case drains are used on hydraulic motors that need to reverse frequently. The motor has drain ports behind the seals so any oil that gets forced past the seals is allowed to drain back to the tank. Without the drain, seals can be "blown" when the flow is reversed.
You will most commonly find case drains on High Flow skid steer attachments utilizing a hydraulic motor. You don't commonly see them on low flow motors.
What model is your backhoe? Have you traced the line and located its source?

Quote: Jerry - 'Check valve would not help since the aux valve is closed after angling the plow. It would have to be a two way relief of some sort between the two angle cylinders. Since the aux valve is closed the most damage you could do is blow a hose but there may be a set-up for this out there.'

Been there. I caught the end of blade on a frozen drift. Most of us don't think about how much leverage there is from the end of the blade to the cylinder pivot point. If you impact load one end of the plow you create a large pressure spike. I didn't blow a hose on the plow, but it did find weak spot in the rubber line at the base of the boom pivot. Of course it was the outer line...
Most inexpensive way would be two pressure relief valves vented to atmosphere or you could add (2) additional tee fittings and two hoses. Since both cylinders are single acting you could "vent" to the opposite cylinder.

 

[Bobcat_Ed]

Quote:
Bobcat_Ed - 'I have one other question on the backhoe side there is a third quick coupling I believe it to be a overflow return line is this ever used in my situation? Thanks, Ed'


I have never seen a skid steer backhoe attachment with a 3d line.
Normally a third line is a case drain line. Case drains are used on hydraulic motors that need to reverse frequently. The motor has drain ports behind the seals so any oil that gets forced past the seals is allowed to drain back to the tank. Without the drain, seals can be "blown" when the flow is reversed.
You will most commonly find case drains on High Flow skid steer attachments utilizing a hydraulic motor. You don't commonly see them on low flow motors.
What model is your backhoe? Have you traced the line and located its source?



Quote:
Jerry - 'Check valve would not help since the aux valve is closed after angling the plow. It would have to be a two way relief of some sort between the two angle cylinders. Since the aux valve is closed the most damage you could do is blow a hose but there may be a set-up for this out there.'


Been there. I caught the end of blade on a frozen drift. Most of us don't think about how much leverage there is from the end of the blade to the cylinder pivot point. If you impact load one end of the plow you create a large pressure spike. I didn't blow a hose on the plow, but it did find weak spot in the rubber line at the base of the boom pivot. Of course it was the outer line...
Most inexpensive way would be two pressure relief valves vented to atmosphere or you could add (2) additional tee fittings and two hoses. Since both cylinders are single acting you could "vent" to the opposite cylinder.

Trihonu, I don't think I explained my self correctly, I am referring to the case drain line on the machine my backhoe only has 2 lines. My question is can excessive pressure caused from the plow cylinder be vented back to the case drain line?

 

[jerry]

Trihonu, I don't think I explained my self correctly, I am referring to the case drain line on the machine my backhoe only has 2 lines. My question is can excessive pressure caused from the plow cylinder be vented back to the case drain line?

It would seem that you could put a relief in each cylinder hose and run them together back to the case drain fitting , might be a very good thing if you are going to do much plowing for others with hidden things beneath the snow.

 

[TriHonu]

It would seem that you could put a relief in each cylinder hose and run them together back to the case drain fitting , might be a very good thing if you are going to do much plowing for others with hidden things beneath the snow.

As I think about this, the mechanics are two-fold:
If you catch the end of the plow the cylinder on that side will create a pressure spike. The cylinder on the opposite side is trying to extend and if it did, would create a vacuum in the other hose.
Having a pressure release in the first line would allow the over-pressure to return to tank. However the question I have is how much counter-force is created by the vacuum in other cylinder?
Based on my experience, the vacuum force may be minimal.
So as Jerry stated, having two pressure reliefs tee'd into one drain line should work fine. The only question that remains is how high to set both pressure relief valves to allow them to operate below the force necessary to blow a hose or damage the plow. I would probably set them both low and increase if the plow is changing angle without an impact load.