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.

J_J · Sep 23, 2005

The steering circuit is in front of and in series with the lift and tilt valve, and has priority. I believe this is for safety reasons.

blackwell · Sep 23, 2005

All regulatory groups require this, OSHA, Automotive (SAE), MSHA, and others. Steering must take priority, does not mean that other functions can't operate at the same time, but steering must work if all others stop.
As stated before, the steering valve only outputs a fixed flow per rev of the steering wheel, reguardless of the flow to the valve. This is done by a gerator element (a pump) that is turned by the steering wheel dumping oil under pressure equal to the displacement of the gerator. On small PT's that is about 7 cubic inches of fluid per rev on the steering wheel. When the engine is not running, thru a series of checks, you can mussle the wheel to pull oil out of the tank and steer the PT with mussle power.
As stated before, the steering valve is in series with the lift valve which allows the steering to take priority, but when not used, all the flow goes to the lift valve thru the power beyond port of the steering valve. The relief valve protects both valves, since it is the first thing in the circuit.

blackwell · Sep 23, 2005

Yes, still have a 2445 and 2460. Total of seven PT's at all locations.
EB

Charlie_Iliff · Sep 23, 2005

The steering circuit is in front of and in series with the lift and tilt valve, and has priority. I believe this is for safety reasons. 
Right - that's how it is now. I was talking about what might happen if someone replumbed the two in parallel instead of series. I think then the steering might only work if you were also lifting or curling - and vice versa -- not exactly the effect desired. /forums/images/graemlins/grin.gif

Spiffy · Sep 23, 2005

OK Dead horse alert on me! /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif

But the last several posts seem to confirm what I was thinking (even if my communication leaves much to be desired compared to Blackwell, Charlie, and Bob). So, unless I'm stuck in an incorrect assumption (still very possible): the Only way this would be effective would be putting a solenoid in to allow the parallel flow only when desired.

Spiffy · Sep 23, 2005

Am I the only one who found humor in the asumption that an eletrical guy might condsider jj to be either imaginary or negative? /forums/images/graemlins/grin.gif If so, my appologies for the lame attempt at humor. /forums/images/graemlins/crazy.gif

J_J · Sep 23, 2005

Parrallel to me means that each branch would have use of the available fluid. At rest, the fluid would go to tank. If sterring is activated, full force would be applied. If driving straight, full force would be available to the lift circuit. If turning and lifting, both would operate, but at a reduced rate.

Spiffy · Sep 23, 2005

You are right about the parallel, but if both are open center, the "open center" is the path of least resitance, then by plumbing in parallel it will actually flow to [and straight through] which ever one isn't being used.

BobRip · Sep 23, 2005

( You are right about the parallel, but if both are open center, the "open center" is the path of least resitance, then by plumbing in parallel it will actually flow to [and straight through] which ever one isn't being used. )

I agee. This is the point I was try to say with too many words perhaps.

Bob Rip

J_J · Sep 23, 2005

I just looked at my Hydraulic CD, and came to the conclusion that I only need to use a flow divider valve in place of the tee that I had mentioned earlier. This will isolate both circuits and provide fluid to both, steering and lift/tilt. The steering and lift pump on my 1445 is a 1.5 to 3 gal pump.

cqaigy · Sep 23, 2005

steer the PT with mussle power. 

I tried this out and did get it to turn a little, but wow it was pretty hard to turn. Maybe if the PT was moving it might have been easier.