Hydr only working 1-way after implement change

MadReferee · Nov 23, 2004

First of all there is nothing wrong with your spool valve, it just may not be the right one.

Check the ID tag on the loader joystick valve to see that it is an L2213A and not the L2203 which is a 3-way valve. I believe that the LA723 loader now comes standard with the L2213A 4-way valve but yours may be the L2203. This will definitely explain your problem. One of the links than ronjhall gave will explain what is happening.

The fact that it worked correctly in one direction tells me that you probably do not have to bleed/prime the center hose and that the problem is most likely the valve being 3-way instead of 4-way.

SeanInMN · Nov 23, 2004

I do have the correct (2213A 4-way) valve. I have an outstanding service call into the dealer to have them come out and look at it. The sales guy verified that I have the right valve and that the Left/Right operation on the blade was working, prior to delivery, with current plumbing.

Sean

DDT · Nov 23, 2004

I have the same problem with my L5030 front blade, I found out when swinging right there is a second detent ( like you want to dump the loader bucket fast) Try to pull the lever all the way to the right and that is the only way mine works. I do not know why but it works for me. Let me know if it works.
DDT

Henro · Nov 23, 2004

Henro, you just failed hydraulics 101. 

I don't think so...

Whether there is air between the cylinders or simply fluid, the pressure that is applied to the high pressure end is felt across both cylinders. The air between the cylinders will compress, and while this is happening the first cylinder may move while the second doesn't. Thus jerkyness is apparent. If you think this is not the case, then you might want to open your hydraulic books again...

Actually, in parallel set up, the force is not less at all, but rather set by the pressure of the pump. The pump pressure is applied to each cylinder independently, and each cylinder produces maximum pressure, which is the procuct of cross sectional area and pump pressure. So, since pump flow is a set amount, speed reduces over the series hook up, but pressure is maximum. This IS simply hydraulics 101...suggest you review...

Generally, what happens in any kind of system, is that if the power source is the same, if you change something to increase speed, you reduce force. A series hookup divides the force between the two cylinders, but increases system speed. If one believes it is possible to double both speed and force, then he might also want to check into options on perpetual motion machines.

We need to apply a little common sense here.

If the series hook up moves in one direction and not the other, but then when the hoses feeding it are swapped, and it now moves in the other direction but not the reverse, then the problem is not in the hook up between the series cylinders or the mechanism that is attached to them. The problem is in the supply side.

This is simply mechanical systems trouble shooting 101.

Sorry. I just have too many years of industrial systems troubleshooting experience under my pre-retired belt to accept an unjustified failing grade... /forums/images/graemlins/grin.gif

SeanInMN · Nov 23, 2004

Problem solved, and DDT had it right--boils down to operator error. There IS a second detent, way out to the right that I didn't realize was there. You have to move the joystick to the right, then push hard to move even further to the right. Likely most of you FEL users know about this already, but nobody mentioned this in my walkthrough, and I didn't see it mentioned in the manual. So I was moving the joystick to where I thought it was hard over to the right, which isn't enough to push the blade back.

Prior to reading DDT's note, I'd called the service dept at Kubota dealer today. The service mgr said at first that it sounded like a problem in the valve, but checked w/the mechanic who set my tractor up. The mechanic explained the second detent and said he also had no idea why it worked this way on the Kubota blade.

Thanks for all the info from everyone--a good discussion, at any rate, about hydraulics.

Sean

MadReferee · Nov 23, 2004

( A series hookup divides the force between the two cylinders, but increases system speed. )

Henro, I'll do even one better than quoting my textbooks.

I did a little search on the internet just now and found this site . It has simple descriptions and even has color pictures /forums/images/graemlins/shocked.gif. The first picture is a series connection and it totally contradicts your theory while verifying my textbooks. Now I am not a college professor but I am an engineer and a picture speaks a thousand words /forums/images/graemlins/cool.gif.

Since the original example had 2 identical cylinders with the same volume, no multiplication or division takes place.

Furthermore, since I do not want to get into a situation of playing mental ping-pong with you on a subject whose theory is no longer in the forefront of my little abused brain (I don't drink Iron City either, just Bud) /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif, I think I will have to agree to disagree with you. /forums/images/graemlins/blush.gif

Till later...

keeney · Nov 24, 2004

Even though the problem is solved, I'll throw in my $0.02.

The series hookup as shown doesn't really do anything other than acting as a convenient way to seal the extra ports on the cylinders and keep the retraction side lubricated (vs. dry). Having oil in there may be important for lubrication of the cylinder seals and bearings.

The un-pressurized cylinder would move in its retraction direction regardless of the fluid flow because its also mechanically connected to the pivoting blade being pushed by the other cylinder.

If the cylinders were dis-mounted from the pivoting blade, then the fluid flow in the center hose would be required for retraction.

It adds no force since the total force from the first cylinder is split between its pushrod and pushing the fluid into the other cylinder. However the forces balance, it still going to be the same total.

If the two cylinders were different sizes, things would get interesting.

The two-cylinder setup is used over a single cylinder in that both the left and right directions operate using the extend function of the respective cylinder, so it moves the same speed in both directions. A single cylinder connected to one side of the blade would move faster in the one direction (with less force) when retracting vs extending.

- Rick

khd · Nov 24, 2004

And that leads to my question. Why the DA cylinders? Is it because they have these cylinders laying around and is cheaper to use what they have then to purchase SA's for this purpose or is it...and this is a thread that I was going to start for a project I am contemplating.....Can or can not a DA spool on a valve operate two single acting opposed cylinders that have some sort of mechanical means to retract one while the hydraulics extend the other as in the blade design? I know snow plows for trucks usually use SA cylinders but I don't know if they are using two SA spools, one for each cylinder.

Just something I've been wondering that maybe someone can answer.

Regards,
Kevin

Henro · Nov 24, 2004

I did a little search on the internet just now and found this site . It has simple descriptions and even has color pictures . 

MadRef,

That is a nice site and a good reference for basic hydraulics.

Unfortunately, it does not picture the situation that was the topic of this thread, two hydraulic cylinders hooked in series, being supplied pressure by one pump.

I mention this not for the sake of playing mental ping-pong...but simply so whomever happens to read this thread in the future will not be side tracked down the wrong road.

A picture certainly is very valuable for communication of ideas. But the picture has to be one of the situation being discussed. The article you referred to shows two cylinders, but one is essentially acting as the pump, since it is outputting pressure and flow when a force is exerted against it.

Anyway, the problem was solved, and turned out to be external to the cylinders...glad the story has a happy ending... /forums/images/graemlins/smile.gif

rambler · Nov 24, 2004

Yea, the 'float' position I mentioned got you. /forums/images/graemlins/smile.gif On my tractors it is power first, go farther & then it goes to float. Your tractor is the opposite - float, then power.

Rick got the plumbing description right - it doesn't need oil in the middle as I was thinking - I had that wrong - as there is a mechanical connection to make the 'other' cylinder retract. They simpley put a hose between to seal the system & keep the cylinders clean in a potentially wet & corrosive environment. It would be possible for them to just put a vent on the 2 unused ports. The hose is probably better.

--->Paul