Hydraulic steering help

[oldnslo]

The problem I have is that when I'm driving the sled, if I'm on smooth hard ground the steering works great. If I am on a soft track, or if a tire hits a dirt clod or something when I'm backing up it will kick the tires out of line. It pushes the fluid right out of the cylinder and the tires will flop around and this is with me holding the steering wheel still. I know this setup works, almost every other sled out there uses one just like this. The only thing I'm not sure of is if they are using a different steering valve? I can't understand why the pressure could be just pushed out of the cylinder like that.
Can anyone give me ideas what may be wrong?
Justin

Justin,
Are their any valves between the gear type flow divider and the steering cylinders?
Are their any valves between the steering unit and the gear type flow divider?
How are the steering cylinders plumbed? Both rod ends together and both cap ends together or one rod end and one cap end?
Which end of the cylinders is connected to the gear type flow divider?

From what you describing their is a flow path created by pressure that allows the steering cylinders to move when the mechanical advantage builds pressure in the steering cylinders. Some gear type flow dividers have relief valves in each leg to prevent over pressurization in one of the circuits. You may need to install pressure gauges at the steering cylinders to determine at what pressure the cylinders start to move and then trace back to where the leak point is. I believe some steering units also have work port reliefs built into them but not 100 sure on this.

A possible test:
With the engine off can you remove the tank line hose from the steering unit and then apply a mechanical load to the steering cylinder like you are driving and hit a rock. If fluid comes out the tank line when the steering cylinders move the problem would then appear to be in your steering unit.

 

[Farmerford]

Parkerfly:

The picture is not clear, but I looked hard and could not find a flow divider where the supply line from the valve splits to go to each cylinder. If there is not a flow divider there, I think I know why you have a problem. Before I give you my thoughts, can you confirm where the flow divider is located and how it is plumbed?

Thanks.

 

[oldnslo]

Farmer,
Good catch on the flow divider location.

Roy

 

[Farmerford]

Roy:

Thanks.

Note that the cylinders appear to be arranged so that both cylinders move the same way on a turn: that is, both extend on a right turn and both retract on a left turn or vice versa. If that is true, then they are in effect two cylinders connected in parallel; base to base and rod to rod. And when you then push on one cylinder to retract it, the fluid expelled from the base end flows to the base end of the other cylinder to extend it. In this case, the wheels then move in opposite directions and splay out or in.

When on a smooth surface the light loads trying to turn the spindles don't overcome the stickiness in the cylinders, but in soft earth or gravel, the drag forces both spindles to rotate away from the direction of travel of the machine and the plumbing does nothing to prevent that.

If I am right, the elegant solution is to install a flow divider on the base lines. The cheap solution is to reverse the hoses on one cylinder. The wheels will not turn through their angles of motion at the same rate, but I suspect it will be close enough for Parkerfly's purposes; at full extension and full retract they will be the same. Come to think of it, my old Club Car golf cart I use around my land is more out of line than that; lots of toe-out going forwards and backwards.

 

[Farmerford]

I neglected to point out that reversing the connections on one cylinder will tie their motion together because of the difference in displacement between the rod and base ends of a cylinder. Depending on the load that might increase the pressure in the lines and cylinders above system limits unless there are reliefs in the steering valve power ports.

 

[aczlan]

Parkerfly:
The picture is not clear, but I looked hard and could not find a flow divider where the supply line from the valve splits to go to each cylinder. If there is not a flow divider there, I think I know why you have a problem. Before I give you my thoughts, can you confirm where the flow divider is located and how it is plumbed?
Thanks.

Looks like there is a tee there to me. That would allow the wheels to bounce around however they liked.
Attached is how it looks like they are currently plumbed and how I would plumb them to get rid of the problem.
The red line is the one that makes it turn right (as seen from the cab) and the blue one is the line that makes it turn left.


Aaron Z

 

[Leejohn]

I well still go with it being the wrong steering valve or bad one. The A and B ports aren't getting all the way closed or blocked off in N. Thinking more as being the wrong valve.

 

[aczlan]

I well still go with it being the wrong steering valve or bad one. The A and B ports aren't getting all the way closed or blocked off in N. Thinking more as being the wrong valve.

Its the tees. With the tees in there (assuming that its still plumbed as shown in the picture), he could disconnect the lines from the valve and cap them and he would still have the same issue.
Look at my "Current" diagram and imagine the ram on the left being compressed while the ram on the right is being extended and see where the pressure will go.

Aaron Z

 

[Xfaxman]

If any of you all are familiar with tractor pulling, I have one of the sleds that the tractor pulls. It has a set of wheels on the front that lower to pick the pan up and steer to drive the sled around when its not being pulled. This steering setup does not use a tie rod, but an individual cylinder on each wheel and the line going to them runs through a gear type flow divider to keep the wheels in sync. My sled has a cab off of a Case 1660 combine, and the steering valve is the one that was already in the cab. I just put a priority valve in my system to feed the steering valve 4 gpm at 1500 psi.
The problem I have is that when I'm driving the sled, if I'm on smooth hard ground the steering works great. If I am on a soft track, or if a tire hits a dirt clod or something when I'm backing up it will kick the tires out of line. It pushes the fluid right out of the cylinder and the tires will flop around and this is with me holding the steering wheel still. I know this setup works, almost every other sled out there uses one just like this. The only thing I'm not sure of is if they are using a different steering valve? I can't understand why the pressure could be just pushed out of the cylinder like that.
Can anyone give me ideas what may be wrong? Going to a tie rod setup would mean redoing everything I've already done, and I'm not convinced it would solve the problem...I think it would keep the tires in line but still kick them around whichever direction it wanted. I attached a couple of pictures to maybe help people have an idea of what my setup is. Thanks.

Justin

I think adding a tie rod and removing one cylinder would be the best and cheapest solution. Then it couldn't move unless the steering valve moved the fluid.

Your problem is the two cylinders are in parallel, so if you force one in, the other will move out. It doesn't matter what kind of steering valve you have.

Look at aczlan's picture, you could put a pipe plug where the hoses from the valve connect to the tee, and the cylinders will still move in opposite directions, with an external force applied. The fluid just goes to the other cylinder.

 

[aczlan]

I think adding a tie rod and removing one cylinder would be the best and cheapest solution. Then it couldn't move unless the steering valve moved the fluid.

The problem is that the wheels angle in when they are lifted, so he would have to re-work the way that they lift in order to use a tie rod.

Your problem is the two cylinders are in parallel, so if you force one in, the other will move out. It doesn't matter what kind of steering valve you have.
Look at aczlan's picture, you could put a pipe plug where the hoses from the valve connect to the tee, and the cylinders will still move in opposite directions, with an external force applied. The fluid just goes to the other cylinder.
View attachment 348493

Yep, it needs to be re-plumbed to one of the ways that I showed (assuming that it is currently plumbed as shown in the pictures).

Aaron Z