Steering logic.

Bob999 · Sep 23, 2005

J.J. said: Now if you turn and lift at the same time, you will have about half going to each circuit. 

The flow will depend upon the resistance in each circuit and I think, in general that the flow will not be balanced. Rather I think that most flow will tend to go to the circuit with less resistence. In the situation you posit I think that could lead to an unsafe condition--if you are using the lift/tilt circuit while steering then the flow (or pressure) to the steering circuit would fluctuate and give varying steering results. Alternatively the lift/tilt could be quite variable and hard to control.

Charlie_Iliff · Sep 23, 2005

I agree with Bob. With open center valves, it is my undertsanding that parallel circuits won't work. The open one will flow nearly everything, and the active one will get next to nothing. Closed center valves would work with independent control of the two circuits, but that would have the relief valve the only return when the circuits were both closed, leading to the system always being at max pressure, with significant drag and heat.
I'm sure there's a solution to change the characterisitcs, perhaps with an accumulator, but I just have gotten used to the 1845 steering priority.

Spiffy · Sep 23, 2005

With all my verbosity you still put it better Charlie!

That leaves at least the steering as open center in series with the lift valves also probably open center. So, I'm still thinking that parallel wouldn't be bad if it was only allowed when a normaly closed solenoid is activated [open] with a spring return switch [like a push button]; this does of course assume the $$$ are worth the gains.

J_J · Sep 23, 2005

I had a discussion with the people at Bailey's Hydraulics. They confirmed what I was thinking, that there is variable flow in the steering circuit. If I am only using a little bit of steering, the remaining fluid should be available to the lift circuits. If I lock it to the left or right, the relief kicks in, and sends it back to tank. If you back off the hard turn, you regain the use of the lift and tilt. The more you back of , the more lift and tilt you should have. This seems to make sense to me.

Another question I have is, can you turn your steering wheel all the way around, and can you turn it at all with the engine off?

J_J · Sep 23, 2005

Charlie, Can you not lift and tilt at the same time. If you can, that is similar to parallel operation. I was going to say equally, but on the PT, the tilt should be faster because only one cylinder is used as compared to two cylinders for the lift circuits.

Bob999 · Sep 23, 2005

J.J. said: The more you back of , the more lift and tilt you should have. 

As I understand the operation of the steering valve it is only "drawing" fluid ( or allowing fluid to flow to the steering cylinders) when 1. the steering wheel is being rotated and, 2. when the steering wheel is against the stop. As I understand it no fluid flows from the steering valve to the steering cylinders when the steering wheel is stationary and not against the stop. If that is in fact how the Steering valve works then "backing off" more would not change the amount of fluid available for lift/tilt.

Sedgewood · Sep 23, 2005

As I understand the operation of the steering valve it is only "drawing" fluid ( or allowing fluid to flow to the steering cylinders) when 1. the steering wheel is being rotated and, 2. when the steering wheel is against the stop. As I understand it no fluid flows from the steering valve to the steering cylinders when the steering wheel is stationary and not against the stop. 

Right - as I understand it, the steering valve can be thought of more like a pump. In PT's case, with a power beyond option. Turning the wheel pumps fluid to/from the steering cylinders (er, rather, allows fluid to flow to/from the steering cylinders proportionally to wheel rotation and only while the wheel is in motion - move the wheel a little, get a little squirt - move it a lot, get a lotta squirt /forums/images/graemlins/tongue.gif). How it functions to block the power beyond at full lock I haven't tried to figure out. If anyone wants to take a crack at it, at my website {HERE} I have links to download the service manual (in PDF format) either from my site or directly from Parker's site.

BTW, Parker claims that if the machine geometry will permit it, it will steer without the engine running but I haven't tried it on my 1845.

Sedgewood

Charlie_Iliff · Sep 23, 2005

J J
I'm not completely sure that the lift and tilt circuits are true parallel, but I suspect you're right that they are. Parallel circuits will both work if both are active, meaning that there is working pressure in both. Where they would cause a problem is if one is open to the return and you try to build pressure in the other. I'll have to stare at some diagrams, but I think if you pull the stick to the side and back, it cuts off the open center. Both lift and curl circuits then have pressure, and each will get part of the flow. If one of those is steering, it will be open when you aren't actually turning the wheel, so lift and tilt won't be able to build pressure. Make sense? /forums/images/graemlins/confused.gif

J_J · Sep 23, 2005

When you are all the way to the left, You are causing the relief valve to kick in, you can hear the whine. and then most all fluid is being sent back to tank. In this situation, I don't believe there is any fluid available to the lift cylinders. If you back off the turn, there is some fluid available for the lift. If you go straight, full volume will go to the lift and tilt. Some one went out and did a test in one of the above post.

This is one of the reasons that we need a good technical manual, and theory of operation. What do you think will happen should Terry ever leave PT. Who will have the knowledge then. We are gaining more knowledge in using these machines than they [PT] will ever have. We are their sales people. They should give all of us a commission, and free shipping.