NH air in hydraulic lines

[HCb]

Hello, All. I have a New Holland TC35A that was bought used with about 300 hours on it about 3 years ago. It has a 16LA loader and a Bush Hog 3 point backhoe. From the beginning I've had problems with the hydraulics, specifically, having air in the lines. The most prevalent problem is when I lower the loader to the ground with the bucket rolled out (usually slightly beyond level for back dragging) and the bucket contacts the ground it will roll back several inches. It is so pronounced sometimes that the cylinders actually contract (the pistons move in) more than 2 inches before the bucket finally stops moving/pivoting and maintains its position meaning the bucket travels 6 or more inches. I've replaced the hydraulic fluid filter, checked the hydraulic fluid level, and cycled the hydraulics more times than I can count. Sometimes, simply cycling the bucket roll out and roll in with the loader about eye level from the seat several times seems to alleviate the problem but it always comes back. It's even got air in the lines on the backhoe and the boom will swing side to side as much as 6 inches as I drive over uneven terrain. I've contacted the dealership where it was purchased twice, several months apart, to see what they say and each time I got the same answer (I was hoping talking to someone else, months apart, might get me different experience on the part of the person I would speak with). They claim that the hydraulic fluid "moves too fast" and causes "vacuum pockets in the fluid" and that the solution is to put a restrictor plate in the hydraulic lines (they did not clearly define where in the lines I would put such a device) which would reduce the flow and cut out the "vacuum pockets" caused by rapid fluid flow. Maybe I'm a cynic but that sounds like bull butter to me. I theorize that vacuum pockets would 1) collapse back on themselves once partway down the line, past the point of occurrence, and 2) certainly not build up as a void in the cylinders. Maybe I'm wrong, but the answer I've gotten from them didn't really make sense to me. My neighbor has a new TC40 and has no such problems (although I'll grant you it is several years newer than mine).

As I mentioned, I've checked the fluid level (at the rear of the tractor on top of the 3 point/differential housing), changed the hydraulic fluid filter, cycled the hydraulics ad nauseum, and still have the problem. It seems most pronounced when I roll the bucket forward/out and I can roll the bucket out to the stop (with the joystick in the first position of roll out (this joystick has two positions for roll out: first is slow/power, the second is rapid/recirculate) and when it hits the stop all the way rolled out it kind of waggles and takes several seconds (I've counted 4 seconds) before it finally builds up pressure with the cylinders and locks the bucket in position and places load on the engine.

It's frustrating and I'm not sure what else to do. I've even checked the return lines for obvious leaks but found nothing amiss.

I'd appreciate any thoughts or ideas you might have.

Thank you for your time.

--HC

 

[beenthere]

Welcome to the forum.
I don't think you have air in the lines. Running the cylinders all the way out, and hold them there under pressure should relieve any air, and cycling them a few times this way should make doubly sure there is not air.

I'm thinking you have a different problem in the hydraulics, maybe in the spool valves.

But as long as you have checked the fluid level, and cycled the cylinders, just seems it cannot be air.

 

[tommu56]

HC

Welcome
It actually it sounds like the lines for the bucket and arms are swapped and you end up in "float for the arms" with the bucket floating.

Is that possible?

Can you let the loader arms float in the detente and the bucket will follow the ground?

tom

 

[kennyd]

Welcome to TBN HC

The "air" in the dump/curl circuit could be caused by "vacuum" pockets like your dealer suggested, and that is what the regenerative feature of the valve is supposed to help-that is the second position of the dump side of the valve. This is commonly called "regen" is is much better explained in the first post HERE.

As for the backhoe...well I don't know, I assume your running the 'hoe from the tractor's system and not a separate PTO pump?

You said:

I've even checked the return lines for obvious leaks but found nothing amiss.

How did you do that? You will not be able to see leaking fluid, but rather since there is negative pressure in the return/suction side it will be sucking in air bubbles. The evidence of that problem is foamy fluid meaning it's entrained with air. Another common suction side leak is the filter...but again it's rare to "see" a leak.

Check your fluid after the tractor is warm-while it's running you are looking for foamy looking fluid.

 

[HCb]

Welcome to the forum.
I don't think you have air in the lines. Running the cylinders all the way out, and hold them there under pressure should relieve any air, and cycling them a few times this way should make doubly sure there is not air.

I'm thinking you have a different problem in the hydraulics, maybe in the spool valves.

But as long as you have checked the fluid level, and cycled the cylinders, just seems it cannot be air.

****
Thank you for your reply. I agree that the cycling of the cylinders should purge them of any air but since the problem seems to recur I guess it is something else or that the air is being re-introduced into the system. I wonder, IF there is air in the lines/cylinders, if cycling them might just move the air from the cylinders to the lines and if the lines are not long enough to still have the air trapped (essentially, the fluid just flows forward a certain amount and then back a certain amount, never making a circuit...but I would think the volume in the cylinders would greater than that in the lines and therefore some fluid exiting the cylinders would make it back to the reservoir).

Not sure. It's been suggested here that the problem may not be air at all. I will finish replying to the other posts and then crack a line open on the loader and see what I get.

Thanks again.

--HC

 

[HCb]

HC

Welcome
It actually it sounds like the lines for the bucket and arms are swapped and you end up in "float for the arms" with the bucket floating.

Is that possible?

Can you let the loader arms float in the detente and the bucket will follow the ground?

tom

Thank you for your reply. The loader does float properly and all the controls work as the device is marked to work (left-right for bucket roll in/out, forward for boom down, second forward for boom float, rearward for boom up).

--HC

 

[HCb]

Welcome to TBN HC

The "air" in the dump/curl circuit could be caused by "vacuum" pockets like your dealer suggested, and that is what the regenerative feature of the valve is supposed to help-that is the second position of the dump side of the valve. This is commonly called "regen" is is much better explained in the first post HERE.

As for the backhoe...well I don't know, I assume your running the 'hoe from the tractor's system and not a separate PTO pump?

You said:
How did you do that? You will not be able to see leaking fluid, but rather since there is negative pressure in the return/suction side it will be sucking in air bubbles. The evidence of that problem is foamy fluid meaning it's entrained with air. Another common suction side leak is the filter...but again it's rare to "see" a leak.

Check your fluid after the tractor is warm-while it's running you are looking for foamy looking fluid.

Thank you for your reply. I read the post you referred to and that explains a lot about the regenerative dump feature. I thought it was simply a "fast dump", I didn't know it worked like that and had the added benefit of eliminating that "floppy" bucket problem. I will try that and see if that works. However, if that is the problem that means that when I dump a load I either have finesse control (first dump position without regen) or wide-open regen dump...but I suppose that if I dump slowly then the problem shouldn't occur (leaving time for the fluid to fill the space behind the piston) and when I want to dump fast use the regen position. I'll see.

I am running the backhoe from the tractor's hydraulic system (from the remote on the back).

I checked the system for obvious leaks...tears in the line, gashes in the tubes, any visible damage to the components. I understand that it's a vacuum side/low pressure side and that leaks might not be noticeable, but I did look for anything obvious like a tear or a gash or some other blatant physical damage.

I will check the fluid. How much air bubbles or foam would be acceptable? I have only limited experience with hydraulic systems and the only other device I have that I could use as a reference would be a log splitter I built; I seem to remember looking in the tank on that thing when it was running and seeing some bubbles at the top but they were kind of large and few and far between like maybe they came from the turbulence of the fluid returning to the tank, not like an emulsion of bubbles like they'd been run through the pump.

Thanks again. And somebody tell me about the etiquette here...I'm leaving the messages I'm replying to above because I think it makes it easier to follow the thread and the replies but if it's irritating (like all caps) let me know please.

--HC

 

[kennyd]

Thank you for your reply. I read the post you referred to and that explains a lot about the regenerative dump feature. I thought it was simply a "fast dump", I didn't know it worked like that and had the added benefit of eliminating that "floppy" bucket problem. I will try that and see if that works. However, if that is the problem that means that when I dump a load I either have finesse control (first dump position without regen) or wide-open regen dump...but I suppose that if I dump slowly then the problem shouldn't occur (leaving time for the fluid to fill the space behind the piston) and when I want to dump fast use the regen position. I'll see.

I am running the backhoe from the tractor's hydraulic system (from the remote on the back).

I checked the system for obvious leaks...tears in the line, gashes in the tubes, any visible damage to the components. I understand that it's a vacuum side/low pressure side and that leaks might not be noticeable, but I did look for anything obvious like a tear or a gash or some other blatant physical damage.

I will check the fluid. How much air bubbles or foam would be acceptable? I have only limited experience with hydraulic systems and the only other device I have that I could use as a reference would be a log splitter I built; I seem to remember looking in the tank on that thing when it was running and seeing some bubbles at the top but they were kind of large and few and far between like maybe they came from the turbulence of the fluid returning to the tank, not like an emulsion of bubbles like they'd been run through the pump.

Thanks again. And somebody tell me about the etiquette here...I'm leaving the messages I'm replying to above because I think it makes it easier to follow the thread and the replies but if it's irritating (like all caps) let me know please.

--HC

Quoting the message you are replying to is great, makes following the thread much easier.

Theoretically, there should be NO bubbles at all visible-it will be obvious if the is to many though especially with the problems you are having.

The one problem that has not been addressed so far is the seals in the curl cylinders, they could be leaking internally causing the "mushy" feeling. An easy test is to extend the cylinders, then remove to hoses from the rod side-now operate the joystick to try to extend the cylinder further...if fluid comes out of the open port then the seals are bad.

 

[Wayne County Hose]

Also, when you backblade or leave the machine parked where there is force pushing the rod in, you could be sucking air in past the rod seals. These seals do a great job of keeping fluid in, but are not made to keep air out. If you have air in the fluid, which all hydraulics do, after sitting, the air separates from the oil and causes a little air pocket. This is common in almost all machines, new included. I have been asked by dealers why their new machines do exactly what you describe and the 2 scenarios I described is all I could come up with. But honestly, I never really researched it too much. Not really a problem, just a weird occurence.

Andy

 

[HCb]

Quoting the message you are replying to is great, makes following the thread much easier.

Theoretically, there should be NO bubbles at all visible-it will be obvious if the is to many though especially with the problems you are having.

The one problem that has not been addressed so far is the seals in the curl cylinders, they could be leaking internally causing the "mushy" feeling. An easy test is to extend the cylinders, then remove to hoses from the rod side-now operate the joystick to try to extend the cylinder further...if fluid comes out of the open port then the seals are bad.

Thank you for your reply. After reading what you posted and thinking about the post regarding the regen position on the joystick I did some playing on the tractor. Here's what I came up with:

Hitting the regen detent seemed to immediately fix the problem of the top cylinders compressing when the boom was lowered and the implement (forks today) touched the ground. Raising the boom and then curling the implement in and then back out rapidly and then lowering the boom caused the cylinders to compress significantly when the implement touched the ground. Repeating that process but rolling the bucket out slowly seemed to keep the problem from happening, without the need to hit the regen detent.

This was with no load on the implement. So I'm a little confused. If it's the load that supposedly causes the implement to lower more rapidly than the fluid can move in to fill the void (on the top end of the cylinder) then I would have expected not to have experienced the problem because there was no load on the implement. Also, I would think that on a double acting cylinder that the way it works is simply apply fluid to one port under pressure and vent the other port to the reservoir. If that's the case then moving the joystick slightly to slowly extend the cylinders would cause the fluid to move slowly into the cylinder, seemingly enhancing the problem of the implement extending the cylinders rapidly causing a vacuum pocket on the top of the piston, not alleviate it. Unless, as the dealership said, it's caused by fluid moving too rapidly and causing the vacuum (some kind of turbulence in the fluid?). That starts to make more sense when I consider that there was no load on the implement to cause rapid extension of the cylinders and therefore a vacuum pocket above the piston.

Theoretically, though, what I'm seeing is a vacuum pocket formed by some phenomena that, when the valve is returned to center, blocking both ports, is trapped in the cylinder (top side only, it seems) allowing the cylinder to compress when pressure is exerted on the implement trying to roll the implement in. Seeing as it takes four seconds (I've counted) from when the implement touches the ground until the cylinders tense up, that's a heck of a void in the cylinders. There should be no way for that much air to get sucked into the top cylinders without having a large enough hole to then leak fluid when under pressure (there are no fluid leaks), and, when there is no load to cause a significant pulling force on the cylinders, it should be simply the fluid flowing into the cylinders forcing them out, not a suction on the cylinders causing them to extend.

I did not check the reservoir for bubbles (yet) after I found what I could do to alleviate the problem, even if it is not a solution. Also, I cycled the hydraulics on the backhoe and it doesn't seem to be slapping around anymore so perhaps I had simply gotten air into the lines from disconnecting and reconnecting it (although I have used it once since I re-attached it).

Where that leaves me is: I will continue to play with the roll-out, roll-in functions, varying speed and see if my first conclusions bear out. I will check the reservoir for bubbles after using it for a while (I had a job to get done today and, after my other observations, just didn't make time to check it today).

Thanks again for your help.

--HC