Hydr only working 1-way after implement change

khd · Nov 22, 2004

I don't have experience with blades but If I look at your first drawing this is what I see: Please correct me if I am wrong here.

Scenario 1: The two cylinders are double acting hence the two ports. If so, you don't get movement because retract is not hooked into the circuit. Extend of one should be hooked to retract of another then valve lines hooked the same way on the two free ports of the cylinders. Position on the valve would only be a matter which way you are comforatble with in moving the handle.

Scenario 2: The two cylinders are single acting with two ports..(I've never seen this but then again). If this be the case then I agree with the others who comented that the "retract" ports that are contected together are not oil filled.

The problem I have with scenario 2 is that even if the two connected cylinder ports are not oil filled you should still be able to compress the air in the closed loop. The other problem: If they are single acting then why does the system need the two extra ports as the push of one cylinder should retract the other because the other cylinder would be on the return side of the valve with free return to the valve and then tank and vise versa.

I vote for number one.

Might be way over my understanding of hydraulics but thats my opinion.

Regards,
Kevin

khd · Nov 22, 2004

Ah nevermind....I looked at it again and am correcting myself....I'm way wrong.

I change my vote. Maybe one line from lift and one line from tilt crossed?

Note to self: Never try and answer this stuff after work on a Monday.

Kevin

MadReferee · Nov 22, 2004

Let me see if I got this right. You have 2 double acting cylinders. When you activate the spool you want one cylinder to extend and the other to retract. Right?

If that is the case then I believe that you should hook up the cylinders as in the second drawing but swap the lines going to the ports on ONE of the cylinders. This insures that high pressure fluid flows to different sides of each cylinder. The other lines will exhaust fluid (under little or no pressure) and return to the same work port on the spool. This will give you the push/pull effect that you want.

As for the first drawing, assuming you bleed the center line going to the top port of each cylinder, and prime the line with fluid, there should be enough pressure to fully retract the opposite cylinder. I could be wrong but I doubt it.

JerryG · Nov 22, 2004

I have seen it plumbed both was, but the way you described is the best. He may have to get a different length of at least one hose.

MadReferee · Nov 22, 2004

The major problem with the first drawing is that the fluid trapped between the 2 top cylinder ports will only circulate between those ports. Not very good for hydraulic fluid and if there is any air in there, well, it ain't gonna work very efficiently if at all since you are relying on that fluid to retract a cylinder at a much reduced pressure.

Henro · Nov 22, 2004

I have seen it plumbed both was, but the way you described is the best. He may have to get a different length of at least one hose. 

Both ways sure seem like they would work to me too. If hooked up like madref suggested, and the hoses were reversed on one of the cylinders, then they would end up being hooked in parallel, rather than in series as is indicated presently.

When hooked in series, the pressure, and therefore the force exerted on each cylinder is halved, but speed is doubled, over the parallel hookup. Air in the middle would contribute to jerkyness it would seem, but it would be compressed and should not prevent the cylinders from moving in one direction, when they are able to move in the other.

Don't forget, apparently the set up moves in either direction when the hoses at the control valve are reversed.

IF this is the case, how could the cylinder hook up be the problem?

I think what MadRef suggest is a good way to do it. Parallel hookup with lines reversed. One cylinder retracts while the other extends. Self bleeding setup too. And slower operation to boot. Only downside would be the cylinders will develop max power...hopefully not a problem...would not want the chute twisted off...

Still...if swapping the lines from the control valve causes cylinder movement to reverse, I can't help but thing the problem is external to the way the cylinders are hooked up...

MadReferee · Nov 23, 2004

( When hooked in series, the pressure, and therefore the force exerted on each cylinder is halved, but speed is doubled, over the parallel hookup. Air in the middle would contribute to jerkyness it would seem, but it would be compressed and should not prevent the cylinders from moving in one direction, when they are able to move in the other.)

Henro, you just failed hydraulics 101.

For the series connection, assuming both cylinders are the same and that there is fluid in the center section of hose, then almost all the force exerted on the first cylinder is transmitted to the second cylinder. Hydraulic fluid does not compress so you have maximum efficiency. If there is air in the center line then most of the force on the first cylinder is used to compress the air rather than to move the second cylinder.

For the parallel connection, asuming you have a constant flow, the flow will be divided between the cylinders. The force will be less and the cylinders will move slower than the series connection.

The real problem for this thread's author is to bleed and prime the center section of hose in the series connection. Since no fluid can flow from the spool into the center section under normal opeating conditions, you must have enough fluid volume there to move the cylinder the length of its stroke. Thus the need for priming which up to now no one has mentioned.

SeanInMN · Nov 23, 2004

I suspect the problem is as Mad suggests--the the dealer did not bleed/prime the center hose section between the top two ports.

As far as hose connections to the valve go, everything IS connected correctly. Up/Down/Float on the blade work properly and I've verified hoses to the vertical actuator go to the correct ports (as compared to FEL). So the only remaining option, at the valve is swapping the two hoses between the two ports. If everything was working, swapping would be just fine--all it does is dictate whether moving the joystick left moves the blade left or right. The manual confirms this, saying that you can swap the hoses, depending on which mapping between the joystick and blade angle you want.

One additional confirmation of hose connections is that the dealer color-coded the front blade hoses and walked through the color-coding scheme with me.

Regarding my diagrams--diagram #1 is showing the setup on the blade, and is how everything is connected now (in series). Diagram #2 is just showing the setup for the FEL (parallel). If I understand Mad correctly, he's saying that you could plumb it both ways, but recommending Diagram #2/parallel, plus switching a hose. I did confirm that Diagram #1 is correct, according to the Kubota manual--so that is at least how they recommend the connection--pistons in series, with short center line in the middle.

So, given that I'm sticking with the "in series" plumbing, it sounds like the consensus is to bleed/prime the center section of hose, which I will try doing tomorrow.

I'm still a little confused, however, on why air in the center line would lead to the blade only working one way. It seems that, if air is in the center line and you apply pressure to left piston, left piston extends, but right piston fails to retract. Fine so far. But when I apply pressure to the right piston, why does it not move? The line goes directly to that right piston, so it seems like it should extend--w/o fluid in the center line, it just seems like either piston would extend, but neither would retract.

...I just tried operating again and here's what happens. Apply pressure to left piston, left piston extends and right piston DOES retract. This seems to imply that there IS fluid in the center line. Then apply pressure to right piston and nothing happens.. (Just to make sure we're looking at the same picture, this is all according to my first diagram--pistons in series). After doing this, I swap hoses at the valve.. Now when I apply pressure to right piston--via the port on the valve that I just used to run to the left piston--the right piston extends and the left one retracts. But now applying pressure to left piston, nothing happens.. In other words, one port consistently works and the other one does not.

Given this behavior, is it still probable that there is no fluid in center line, since the piston on the far side of the center line IS retracting?

I'm sort of migrating back to Henro's theory, which is that the problem is associated with the port on the valve, rather than the pistons. The one thing that consistently does NOT work is that particular port...

What I'll do next
- Hook back up to FEL, to see if the "bad" port works on bucket
- Call dealer to see what thoughts they have

I'll also say again that the dealer (it was actually the mechanic who set up the tractor) told me: 1) he did verify operation of the blade, including up/down AND left/right and 2) he did bleed all lines. I'm guessing that if he really did get left/right operating correctly, this implies that there was fluid in the center line at one point. (Nothing has changed in how the center line is plumbed).

Sean

ronjhall · Nov 23, 2004

Sean
I'm not a expert. But have played with my tractor enough to make me ask some questions.
Have you tried switch the raise lower hoses with the right left angle hoses?
Somewhere I read something about Regen circuit, and 3 way or 4 way valves. I'm sure someone else can add more information to this subject.
Until then here is a thread that mentions the reason for 3 and 4 way valves. Click Here