Need Help Understanding Theory and usage of Valves on Rear Hydraulic Lift

[tjc1989]

Hey guys,

I hate to sound like a dummy, but can someone explain in terms I understand what several of the valves are designed to do and why, on my Branson 4220i rear hydraulic lift? I know somebody out there is knowledgeable enough to help on this.

Specifically the control valve, safety valve, relief valve and stop valve.

And also the draft control.

I am enclosing Branson schematics of each valve.

Mine has a front end loader, which is working OK as it should, BUT, the rear hydraulic lift bleeds off and jerks up and down. Or as some have referred to as hiccups. Its worse when cold, with more rapid jerking, and gets better somewhat when fluid is warm. But even when warm, does not go away. It shakes the whole tractor, if I have a heavy load on the lift , such as an 800 pound tiller.

I took it in to the dealer I bought it from when it was in warranty, and the mechanic advised me he didn't find much wrong with it, but did replace a piston o-ring on the hydraulic piston, and fine sandpapered a small spot on the cylinder. When I got it home, and lifted something , it still did it. I didn't take it back, though I should have. But after having my tractor for 10 days, I was very reluctant to take it back in. PLus the inconvenience, and my lack of confidence in them. Now its out of warranty, and I am going to try and fix it myself.

But I have some lingering doubts on it.

Number one: While rear lift is hiccuping and trying to sustain lift height, if I slightly use my FEL, and slowly lift it up, the jerking nearly subsides all the way, with no loss of rear lift height. When I stop the FEL lifting, it goes back to the jerking. It seems that somehow, the use of the FEL lessens the effect of the jerking, and does not cause the rear lift to drop in height.

A little history:

Tractor has 338 hours.

I have changed fluids and filters twice. I am using Shell universal tractor fluid, and Branson filter. Fluids or filters made no change.

I have tried changing settings on the valve that controls the rate of rear lift drop, by tightening the knob tighter or looser. No effect.

I have tried changing the draft setting by moving the draft control lever to high number and low number. No effect.

So, I am preparing to pull this unit off my tractor and get into it. My fear is that if I can't find anything wrong with the piston or cylinder, then what. I have a very good mechanical background, but don't know what the fluid valves are designed to do.

Thats why I am asking for theory behind the various valves used on the hydraulic lift. I'm pretty sure the Branson dealer mechanic did not touch any of the hydraulic valves when he had it apart.

So is it possible a pressure relief valve could be malfunctioning, or another valve? Could a misadjusted draft control cause this?

I would really appreciate some help on this. Thanks, in advance.

 

[Jerry/MT]

Hey guys,

I hate to sound like a dummy, but can someone explain in terms I understand what several of the valves are designed to do and why, on my Branson 4220i rear hydraulic lift? I know somebody out there is knowledgeable enough to help on this.

Specifically the control valve, safety valve, relief valve and stop valve.

And also the draft control.

I can give you a general idea of what the various valves do but without the hydraulic circuit diagrams it's pretty hard to be more accurate .

The control valve controls the up and down movemnet of the three point hitch. Depending on the setting, it usually also controls the mode of operation of the hitch; draft mode or position mode. Draft mode is made for ground engaging implements( i.e. a plow or mounted disk). Draft is sensed either through the top link compression ro the lower links and if the draft force increases above the set value, the lift will raise the implement and if it lowers below the set value, the control will lower the lift.

Likewise position control will try to hold position of the 3 pt. If there is a leakdown of pressure in the lift cylinder, the hitch will lower and the position control will activate and cause the lift to raise to its set position. this is probably what is causing your hitch to hiccup.( My Ford 4610 does this with a 1250# bale on the hitch.)

The relief valve limits the hyraulic system mak pressure to some preset value that is the limiting normal applied force for the lift cylinder. If you try to pik up a rally heavy loadthe relief valve will protect the system by opening and discharging the fluid back to the reservior.

I'm not sure that i know what the safety valve is for. It might be similar t the relief valve and protects the system in the event of a failed relief valve or it may have a higher setting to protect from some sort of overpressurization of th the system due to dynamic effects. I really don't know.

I don't know what the "stop valve" is for.

Hope this is helpful to you.

 

[tractorski]

My Branson 3510 had the same hiccup, it didn't affect the ability of the tractor. It was very annoying though.

 

[oldnslo]

TJC,
I agree with JerryMT some where in your lift circuit there is a leak that is causing the arm to "bleed down" and then the position sensor raises the arms back up. I.e. the hiccups.

I would look first at what oil is under pressure when the arms are raised and where are the potential leak points?

Lift cylinder and main control valve would both be seeing pressure. Not sure sure about other components.

A thought: Since using your loader slows or stops this I would look for the main control valve not returning to center position properly. Reason for my thinking is that the only logoical reason using the FEL would stop this is that you are either adding flow to replace the leak or plugging the leak with the increased inlet pressure. Both point towards the main control valve.

NOTE: I know nothing of how this valve is configured and the diagram you posted does not give any parts break downs.

Dumb question but simple test.

With no load on the 3pt arms and the arms lowered, do they move/ raise when using the FEL under load? Again would point towards main control valve.

Best of luck

Roy

 

[J_J]

The safety valve is a relief valve, and I believe it relieves if the load is to big. I believe that the stop valve is a knob adjust to vary the speed of lift or close off all hyd fluid to the 3pt.

 

[tjc1989]

Jerry/MT , oldnslo, and J_J,

Thanks for taking the time to read and respond. To clarify, Control Valve,
Position Control, Main control. If you look at the schematics I posted, does the control valve under the bottom do all three of your answers?

In other words, is this the valve that holds position control? And regulates flow to the cylinder?

And J_J, IF the safety valve is another relief valve, Do you know how either the relief valve or safety valve could be affecting the pressure on the lift piston?

I guess I am just trying to get a good pointer to try and zero in on the correct valve to clean and inspect. Of course, I will probably do all of them.

I am going to post another schematic, showing an overview of the system.

Its another story, but the dealer jerked me around horribly on some other minor warranty work, and who knows, maybe the mechanic never even put in a new piston o-ring. But assuming he did what he said, thats always led me to believe that some sediment , cuttings or trash is interfering with one of the other valves. That would explain why he did not fix it.

Obviously, pressure is bleeding down somewhere, either past the piston, or another valve.

On my tractor, high pressure fluid goes to the FEL joystick valve, then on to the rear lift through a hose. Is there any reason to suspect trash in the FEL valve?

 

[J_J]

Do you have the hydraulics schematics available.

If the 3pt does better when using the FEL, it is probably because the only fluid going to the back is the fluid not used by the FEL. If the FEL is only using a few GPM , then the rest of the pump volume is gong to the back, and you might not be getting the relief pressure.

Have you put a gage in the circuit and wrote down all the readings?

There are two relief valves, why exactly, I don't know. One might be for input pressure relief. and the other for draft relief.

 

[oldnslo]

TJC,
in looking at the diagrams you posted I would have to say the "Control Valve" would be the first place I would look. Be very careful taking this apart because it looks like there could be lots of parts to loose from spring loading.

Do you have a part description to go with the exploded views? If yes this might help narrow down potential problem areas.

Roy

 

[tjc1989]

J_J,

No, sorry. It would sure make life easier if I had something better. The Branson manual supplied with purchase leaves a lot to be desired. I have gone through every page to try and determine fluid flow through this thing, and what I posted is as good as it gets. The little manual that came with the loader is no help either. If I knew where to purchase a comprehensive repair manual , I would.

I used to be an automatic transmission mechanic in an earlier life. It was nice to have manuals that showed color coded fluid flow through each band servo, and clutch pack, torque converter, pump, and planetary gear pack lubrication, etc. Plus testing procedures and points, etc.

In research, I ran across others having similar problems. Nice to know its not unique to Branson brand. One user, bdblount made a post on 9-21-2008 in repair section of the forum, complaining on a John Deere for problems similar to mine, where he noticed issues with his loader and rear hydraulic lift. Not exactly like mine, but similar. You might check it out. I noticed several other posts where users had similar rear hydraulic issues, but it seems none ever got resolved.

The answers he got were like you guys" answers, pointing to position control valve.

For me, its way too annoying. Mine doesn't just bump back up every minute or so, it does it 2 or 3 times a second, jerking the whole tractor. This can't be good for that much force to be banging so frequently.

 

[tjc1989]

Oldnslo, thanks. Here is the parts list.