Steering logic.

[BobRip]

Since flow it going back to the tank except when a section is being moved, this would mean that when (for example) the steering is engaged to change steering angle, most of the flow would revert to tilt and lift circuit and there would not be enough pressure to do much steering. Only if both were engaged would there be enough back pressure to do work and then the flow rate would be 1/2. In other words when lift/tilt and steering, are not being changed you would have return flow to tank from both system. When one is engaged to change angle most if not all of the flow would return through the other system and little pressure would be available to do work.

Bob Rip

 

[J_J]

Bob, I tend to disagree for this reason. After modification, if you have a 10 gal pump, and you activate only the steering motor, you will have the full 10 gal available to make your turn at maximum turn rate. The same will occur if you only activate the lift circuit, you would have the full 10 gal available, fast lift. Each system has it's own return line to tank, therefore, they are separate. Now if you turn and lift at the same time, you will have about half going to each circuit. Med turn, and med lift. Neither output will get in the way of the other. You will be using and dumping 5 gal from each circuit. I believe this is correct, but let me know if this logic is not valid.

I just don't like the priority setup as it is now. I can live with it till I get it changed.

 

[Spiffy]

Once again without time to take a closer look at the schematics (I don't recall it showed anyway), I may be typing out of turn:

but it depends whether each is open or closed center. I'll almost bet at least one is; likely steering; maybe both. This would require an auxillary solenoid(s) for your mod to work (to "close" the open center(s) when required); of course, then you need the switch(s) located conveiniently - perhaps a button on the joystick. Could be more trouble than value. /forums/images/graemlins/confused.gif

 

[Highridge]

</font><font color="blue" class="small">( MR: You guessed it; I'm contemplating a rear joystick to make BH life easier. Also would be great if I ever mount a 3pt blower; I think it'd be a snow moving machine with a blower on one end and snow bucket on the other. )</font>

If you ever did that, you would DEFINITELY need to take some pictures! /forums/images/graemlins/cool.gif

 

[J_J]

Open-Center: Typically used with a fixed-displacement pump, allows oil to free-flow back to the tank in neutral position. Shifting the spool redirects oil to the selected work port,
therefore in our situation cutting off, or reducing fluid down stream. If you do a 10 degree turn for instance, you may allow some fluid to slip by. If this steering system had power beyond, I don't believe I would have started this thread.

Closed-Center: Typically used with a variable-displacement pump, oil flow is blocked at the valve until the spool is shifted from neutral.





Open Center is the type valve/motor I believe is used in the PT's.
Therefore the output from the pump is available to either, steering or lift. They must be is series for the steering to affect the lift. In a lift situation, the fluid is going through the steering valve to the lift valve. Each has an output to tank. If you activate the steering, you interrupt the flow to the lift valve, which is exactly what is happening in my situation. Therefore if I separate them, they should work independently.

 

[blackwell]

Its the law.

 

[blackwell]

Not true. The steering meters oil to the steering cllinders at a fixed rate per rev of the steering wheel reguardless of the flow going thru the valve. The only way to increse steering speed is to increase steering valve displacement or decrese cylinder volume. The law requires the steering to take priority. The reason your machine wont lift when the steering is to one side, you are continuing to try to steer when the machine is fully steered, thus opening the relief and not allowing oil to the lift valve. This is the same thing as the little old lady coming out of a parking trying to steer her car more after the steering has hit stops and the belt is squalling due to the steering pump at max pressure.
On Pts the flow goes thru the steering and then to the lift valve, so what is not used steering can be used to lift. Try lifting the arms and steer slowly, you will see the arms slow down, then stop steering and they will speed up.
Try not to squill the belt! /forums/images/graemlins/blush.gif /forums/images/graemlins/cool.gif

 

[BobRip]

J J this is kind of hard to explain in words, but I will try again (and I am not an expert on hydraulics, but I am one on electricity). If the flow is 10 gallons per minute with no change in lift or steering then half will probably go through each of your new parallel circuit. The pressure is very low since these are both free flowing circuits. When you try to turn for example the flow will be restricted through the turning circut and back pressure will try to build up. Since the lift/tilt has not been activated and has little or no back pressure then most (if not all) of the flow will go through this circuit and you will get little or no steering force. Remember, in hydyaulics the flow is greatest when you are not changing the position of a cylinder.

At maximum steering forced to the end of travel the pressure builds up and trips the relief valve because there is no flow. In this situation, since there is no flow through the steering, then the tilt and lift get no pressure in PT plumbing system. In your approach, the pressure would not build since it would flow through the tilt system.

To use an electrical analogy if you have two wires in parallel providing power to a light bulb and the wire lengths and diameters are equal then the currrent (which is actually electron flow) will be the same in each. If you make one of the wires longer then you have more resistance and the current will shift to the wire with less resistance.

If you decide to do this, please make sure you can change it back. Remember if you just stay off the stop then you can still do lift.

Sorry for the long explanations and good luck with what ever you do.

Bob Rip

 

[J_J]

Are you talking about legal law, or laws of hydraulics? If you are talking about legal law, is there a precedent that requires this type of circuit?

 

[BobRip]

J J, I wonder if something is wrong with your particular machine. Please confirm that you do have lift control when you are not at the stops of steering. If you do not then it could be the relief valve is stuck partially open or relieves at too low a pressure.

Bob Rip

 

[J_J]

Are you saying that there is a fixed orfice in the valve that only allows a certain flow to go to the steering cylinders? I am thinking that the more you turn, the valve opens more, and if you turn all the way to one side, you decrease the fluid going to the lift cylinders. In a partial turn, some fluid gets by. Is this correct?

 

[J_J]

While steering, there is only a little lift. When I stop steering, I have full lift.

 

[BobRip]

I just drove my 422 to test this. When steering (4 in bucket installed and empty) I can easily raise and lower the bucket and tilt it. If I hit the lock at the end of steering then the tilt becomes real slow. I think you have a mechanical problem with some part, not a design issue. I suggest you call PT and describe the problem to them.

Bob Rip

 

[J_J]

My 1445 is an early 90's. After searching the web, I came across an article about hydraulic and safety, so maybe it is the law. I think my 1445 is working like it is supposed to. Steering has priority, and does stop most of my lift. I just don't like it that way. An analogy might be, when you are using a backhoe, and you want to swing the boom and uncurl the bucket at the same time.

 

[BobRip]

Your machine may operate differently from my 422 so it's hard to tell. I would still discuss this with PT people.
OK, enough said.

Bob Rip

 

[Spiffy]

Blackwell, good to see you! I presume you still have a 24XX.

Can't let these (1)4XX guys have all the fun. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[Spiffy]

<font color="blue"> (and I am not an expert on hydraulics, but I am one on electricity) </font>

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

j j [caps intentially incorrect], I'm afraid you won't be able to communicate with Bob. He thinks you're imaginary. Of course, that could be j*j in which case you are real, but negative. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[Spiffy]

Ok, assuming nothing wrong with JJ's machine and also that it is plumbed similar to newer models:

Then I'm thinking he may get away with putting a solenoid between the parallel connection he proposed [per Blackwells statement saying [I think he's saying] the ends of the steering are "deadheaded"; this does correllate to what we seem to be experiencing].

This would essentially then bypass the steering (yes, parrellel, but like electricity it will find the path of least resisitance or the combination thereof) at deadhead, and split in varying configurations depending upon loads at less than full steering. Only activated when he pushes a button on the joy stick (or where-ever) it shouldn't adversely affect any operation. /forums/images/graemlins/smile.gif

This make sense? Am I right, potentially right, or way off?

 

[toy]

I know Im not a hydraulic expert by no means but this is just how I think that it works. First of all the pump puts out a constant volum of oil and it needs somewhere to go. The oil goes over to the releif valve. There are two hoses coming out of it. one has a spring valve set to a designated pressure so that the oil can't flow that way unless the designated pressure is reached and in that case the oil could flow through that hose and back to tank. But there is another hose and at the releif valve there is no restriction of the oil flow at that point so the oil will flow through it to the steering valve. The oil enters on the left port so you have a pressure flow to there. now at that point the oil comes in to the steering valve and goes out the hose that goes to the valve bank which is an open center valve which allows the oil to flow back to the tank unrestriced. Now back at the steering valve I beleive there is a steep coarse threaded shaft. When you turn the steering wheel that opens up ports that allow the oil to go to the flow divider and then to the cylinders and then back to the flow divider and then back to the steering valve where it can go back to the tank. Now if you turn the steering valve to where it fully extends the cylinder and fully retracts the other steering cylinder there would be a full flow of oil going into the steering valve and with the sleeve pulled up as far as it can go I beleive it opens up an internal releif port that dumps back to tank and that is what robs the hydraulic fluid from the valve bank now when you back the steering valve back a little then it opens the oil flow back up to the valve bank. as you steer the steering valve it puts enough restriction in the inside of the port where the oil goes out to the valve bank to give you enough pressure to operate the steering cylinders. Sort of like a portioning valve that would divide the oil so much of the flow to go to one place to do that work and so much of the pressure oil going to another place to do that work. On scoops they have a valve like the quick attach valve pull it one way and it steers that way and push it the other way and it would steer in the other direction. and it had another valve to raise the bucket and extend the ram. I couldn't get a diagram to look at when I posted this but I hope I got it right.

 

[tracdoc]

oh boy..... now I really have a headache... wish I understood more about hydraulic valves and circuits /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif