Complete rebuid/seal of control valve (quad, or 8 lines)

Montana Guy · Post by **Montana Guy** » Wed Oct 14, 2009 9:14 pm

I did the rebuild at a big Hydrolic Control Valve shop for $335. The forks (or tilt) are STILL bleeding out quickly? I see no leaks anywhere and the Rams seem fine too? No leaks at all there and the lift of the up motion is very strong. They power down fine as well.It will just bleed quickly down. Not like an overnight leak or anything, i mean it bleeds down as soon as you let off the up motion on the lever. It must be bypassing with-in its self somewhere? Is there a check valve in there? Clues Guys? Lavoy ?
Toby

Post by **Lavoy** » Thu Oct 15, 2009 9:16 am

I would bet that you need to rebuild the tilt cylinder/s, it must be bleeding past an o-ring internally.
Lavoy

Gil · Post by **Gil** » Fri Oct 16, 2009 7:46 am

There is packing at the very end of the piston which seals against the barrel of the cylinder. When you pull the control lever, hydraulic fluid is pumped into the back end of the cylinder, presses against the packing and pushes the piston out of the cylinder. When you pull the control lever in the opposite direction, the hydraulic fluid is pumped into the front of the cylinder which pushes the packing in the opposite direction and the piston rod retracts into the cylinder. Even if there is some leakage around the packing, the high volume of hydraulic fluid will still move the piston. However when the control lever is in neutral and there is weight against the piston rod (like the weight of a loader bucket) the hydraulic fluid may leak around the packing and the piston will be pushed in or pulled out of the cylinder.

Simpler than the hydraulic control to disassemble, you can get the packing and seals to repair it. There are also seals at the open end of the cylinder which keep the hydraulic fluid from leaking out and a wiper seal which cleans dirt off the piston rod when it retracts into the cylinder. These should also ususlly be replaced.

In worst cases there may be scratches in the cylinder wall which act as little channels to let fluid leak around the packing. In this case a hydraulic or machine shop can hone the cylinder and you can use oversize packing or they can cut off the ends of the cylinder and weld in a new cylinder barrel. You should be able to see if this is a problem when you take the cylinder apart and look in it with a flashlight.

Montana Guy · Post by **Montana Guy** » Sun Oct 18, 2009 9:27 pm

Awesome help guys, i am all over it. I did an old ford tractor a few years back and have been around 4o ton hydraulic cranes with some serious rams. Hope those knuckles come apart easier than they look! Wow!!

Montana Guy · Post by **Montana Guy** » Wed Oct 28, 2009 4:41 pm

Help !!! Somebody please give me some direction. I rebuilt the cessna control valve at a hyd, shop and tested good. I still had the forks bleeding out. I pulled both Rams and had a full rebuild/packing at the same hyd. place. It still bleeds out ! What else can be doing this? its on its own circuit(so to speak) so any other leaky line or something should not matter. But everything else is fine. I just bought this damm thing and am in a bind. I am stressed.............

Montana Guy · Post by **Montana Guy** » Wed Oct 28, 2009 6:40 pm

The John Deere guy told me it HAS to be in the control valve and did they test it under "back pressure" at the shop. Well, that is all this large company does..... hyraulics. Control valves and cylinders and the likes. I told the Deere guy i "assumed" it was properly tested and he said not for sure. I flagged the section of valve for the shop and they even photo copied my diagram and highlighted where i believed the problem area of the valve was. I called the shop and asked if it was tested with pressue. Well, yes & no. He said, "well. bring it on down and we will test it again". WHAT !! it was a days wrenching. pulling it out and a day going back in. Then, i rebuilt cylinders for nothing and you say "bring it on over"?
If they let this go out of that shop without proper testing and then i rebuilt cylinders for nothing there too, i am ready to strangle someone.
I willl be on that phone with a shop manager in the morning. I am p o'd like you don't even know.

Post by **Lavoy** » Thu Oct 29, 2009 10:23 am

Pull the hyd hoses off the tilt cylinders, and plug the holes. IF they droop, it is in the cylinder, if not, it is in the valve.
Maybe I should have asked first, does this occur only when running, or if you shut it off, will they droop too?
Lavoy

Montana Guy · Post by **Montana Guy** » Thu Oct 29, 2009 10:38 am

Lavoy, the hyd shop says it needs a load lock put in. That is what i am progressing towards today. But still, THAT is why it was brought to them in the first place. (bleeding off control valve) Yet, they did not even test it to see if it was fixed after a resealing of the WHOLE valve. They are giving me the pilot operated single load lock. Lucky they arn't up here in the snow installing it too. This better work......... It bleeds off quickly running or not ! AND, it seems to be not wanting to lift out of the down position at all?

Post by **Lavoy** » Thu Oct 29, 2009 2:02 pm

There is a problem with the system somewhere, I would not buy the lock. They did not come from the factory with them as far as I know, so it should not need it now. Don't know your shop, but sounds like they are making excuses.
Lavoy

Montana Guy · Post by **Montana Guy** » Thu Oct 29, 2009 6:54 pm

Lavoy, the shop is Catey Control, and they have Given me the Load lock which i installed today. The "Deere guy" and the shop said if the Spool is so worn in the conrol valve that it would have to have one installed, or a new control valve.
Today, the install seems to have stopped the the bleeding alright, but it chatters powering down, and barely has enough lift to roll its own forks back from the down position.
Is it still ALL in that damm Cessna Quad Contol valve? Is it that worn out? Should i actualy take the whole thing back out and into that shop again? Do i try another whole new control valve?
Its possible something with the Hydraulic pump is not right either? It really needs to race the motor to get good lift? The old owner showed me a Cessne pump he pulled out that was slipping at the spline. (had started to pull out, i think) he replaced the pump, but not the female splined end with the flange that bolts to the output shaft on the motor. It being worn has maybe started the slip in the new pump? Lavoy, i am ready to just cry......... where do i turn?

KenP · Post by **KenP** » Fri Oct 30, 2009 4:55 am

deleted

Montana Guy · Post by **Montana Guy** » Fri Oct 30, 2009 7:25 am

Thanks Ken P. I will see what it intails to either fix that control valve or put in a new one? Still. not sure what to do. I have bought this dang thing, and there it sits..........

Post by **Lavoy** » Fri Oct 30, 2009 9:28 am

Do a pressure test on the system as well, you may be under rated PSI, that will really hurt your lift capacity.
Lavoy

Montana Guy · Post by **Montana Guy** » Fri Oct 30, 2009 10:03 am

But, the boom and other contols ALL have plenty of power. It has to be inside that cotrol valve
spool" as Ken P. has said. I am afraid to take it back in to that shop that was "suppose" to fix it the first time. Do i risk it? Plug off that section of contol valve and plumb in a single lever valve to make it happen? Not a big mechanic, but that sounds like it might be the best route for this Montana guy. *sighs

Post by **Lavoy** » Fri Oct 30, 2009 10:37 am

Gothca, didn't catch that. Yes, it has to be bypassing in that spool would be my guess.
Lavoy

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Complete rebuid/seal of control valve (quad, or 8 lines)

Complete rebuid/seal of control valve (quad, or 8 lines)

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