Air seeping into rod seals?
- Thread starter SmallChange
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wdchyd
Elite Member
I’m my experience any air entrained into a hyd system after the pump would be caused by a suction leak at shaft seal or before the pump in suction lines, which leads to foamy oil, then when machine is idle the air separates.
Air theoretically could be sucked in by a bad hyd rod seal but usually a hyd leak shows it’s ugly face before.
Air theoretically could be sucked in by a bad hyd rod seal but usually a hyd leak shows it’s ugly face before.
OP
SmallChange
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- New Holland WM25 with 200LC front end loader, filled R4 tires 43X16.00-20 and 25X8.50-14 (had a Kubota B6200D with dozer and R1 tires)
I think air leakage is possible because:
1) Air leaks much more easily than liquid
2) The oil seals around the rod are designed to hold pressure in only one direction
3) There can be weeks for air to leak on a parked machine, but usually much less than a minute for oil during use
1) Air leaks much more easily than liquid
2) The oil seals around the rod are designed to hold pressure in only one direction
3) There can be weeks for air to leak on a parked machine, but usually much less than a minute for oil during use
LD1
Epic Contributor
Rod gland seals are indeed a lip seal that seals with hydraulic pressure behind it. No stopping air from entering under a vacuum.
But you are overthinking it.....if the "floppy" bucket is only upon startup, then simply start the machine and curl the loader all the way.....and hold the lever for a few seconds after it stops moving. All air is now purged and your ready to go.
OR...is this something that is happening at times while operating? And what machine is this on?
But you are overthinking it.....if the "floppy" bucket is only upon startup, then simply start the machine and curl the loader all the way.....and hold the lever for a few seconds after it stops moving. All air is now purged and your ready to go.
OR...is this something that is happening at times while operating? And what machine is this on?
Tx Jim
New Member
IMHO in order for air to enter a hyd cylinder that is full of oil from previous operation the oil in cyl barrel must leak past a seal or valve in order to be any space for air to enter a sealed cylinder. I agree with LD1 that cycling cyl rod out/in a few times will purge any air that possibly could get into cyl barrel.
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SmallChange
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- New Holland WM25 with 200LC front end loader, filled R4 tires 43X16.00-20 and 25X8.50-14 (had a Kubota B6200D with dozer and R1 tires)
"hold the lever for a few seconds after it stops moving" -- you mean, drive it into relief and keep it there several seconds?
It's only upon startup, if I work it enough to get the floppiness out. But it takes more than curling all the way. I worked on this during a recent usage by putting the tractor on the steepest safe uphill and downhill slopes I have, and working both the motions back and forth to their extremes, making a special effort to get the rod end cylinder fitting as high as possible (though there's still obviously some space above it because it's on the side, and I also don't know how close to the end of the cylinder the piston gets when the bucket hits its travel stop). Only after doing this a few times did I feel the floppiness go away. If I'm not working the bucket to extremes of its travel, for example if I just do a little pallet fork task, the floppiness does not go away. As far as I know, the floppiness comes when the machine is parked, doing a lot of movement works it out until the next time it's parked, and doing a little movement doesn't.
By floppiness I mean, for example, I park the bucket flat on the ground, and when I look days later the edge will be several inches off the ground. I can step on the edge and drive it down to the ground or nearly to the ground. By stepping on it I can make the rod travel at least an inch out of the cylinder. After I've been using it a little bit I can still do this.
This is a NH Workmaster 25 that I bought new. When I did the initial 50 hour maintenance, which called for changing the hydraulic filter but not the hydraulic fluid, I didn't know what to expect and let most of the fluid drain out before I could get the new filter seated. Of course I replaced this ($$$!). I started noticing the floppiness soon after that and had been afraid I'd created a lasting problem, though since then I've started thinking the two were unrelated.
Today is Tractor Maintenance Day. I'm headed out to replace the battery, rinse the machine off, apply Fluid Film, grease things, et cetera. I am going to experiment around a bit more, get as much floppiness out as possible, and park it with both cylinders slightly in tension so the rod end seals have oil pressure behind them. That is, I'm going to put a little stress on them before shutting down, so the pressure may well relieve over a few days, but it will go to zero from the positive side.
By the way, this machine lives in the barn on an asphalt paved floor. It would be very easy to see even a small hydraulic fluid leak, and I always look, but have never seen any.
LD1
Epic Contributor
YES....curl it back and HOLD it on the relief for a few seconds. This will purge the air out.
Pointing uphill/downhill or the orientation of the gland seal is irrelevant.
Cycle all the way to the stops, hold it on the relief a few seconds. Do it full dump too. Won't hurt a thing but 99% sure it will solve your issue
Pointing uphill/downhill or the orientation of the gland seal is irrelevant.
Cycle all the way to the stops, hold it on the relief a few seconds. Do it full dump too. Won't hurt a thing but 99% sure it will solve your issue
OP
SmallChange
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It worked! Parked with the cylinders loaded with a little tension last night, and it's still tight as a drum. I can't feel any softness at all. I can't tell by looking whether they drifted any, as the tension was slight enough that I could only see movement when I tightened them by paying attention. It's not like I could see space underneath anything (and a good thing, as I've no particular animus towards the toads).
By the way, I measured a little more carefully late yesterday, and I was extending the floppy cylinders by very close to one inch, which translated to several inches at the bucket edge.
About the uphill - downhill thing, the point was to keep the cylinder fitting at the upper end. I don't see how I can flush the air out if the fitting is at the lower end. I'd only be able to drive the air into solution in the hydraulic fluid and then cycle that out so it could bubble out at a lower pressure point in the system like the valve or the return tank, which seems like it'd be slower, though I didn't try to cipher that out.
By the way, I measured a little more carefully late yesterday, and I was extending the floppy cylinders by very close to one inch, which translated to several inches at the bucket edge.
About the uphill - downhill thing, the point was to keep the cylinder fitting at the upper end. I don't see how I can flush the air out if the fitting is at the lower end. I'd only be able to drive the air into solution in the hydraulic fluid and then cycle that out so it could bubble out at a lower pressure point in the system like the valve or the return tank, which seems like it'd be slower, though I didn't try to cipher that out.
LD1
Epic Contributor
The uphill and downhill is irrelevant on a pressurized system.
Think of your car....master cylinder is alot higher than your brake calipers where the bleed screw is
Anyway....glad you have a solution that works for you.
But in any case, a simple full cycle extend and retract of the cylinders....with a 1-2 second pause at full stroke while STILL holding the lever would solve the issue.
Vigo327
Platinum Member
Smallchange i think you've got your head all the way around this and don't need any further help really, but as mentioned air can't enter unless fluid leaves, and in this case that fluid is leaving through leakage across the loader valve which really doesn't matter when the tractor is running. So you can choose to 'work around it' through the methods you've discovered, or you can replace the loader valve (i probably wouldn't), or if you want to modify the tractor you could add a 'load holding' valve aka 'pilot operated check valve' where fluid can't leave one side of the cylinder until actual pressure is formed on the other side. This is what keeps things from 'drifting down' in all kinds of hydraulics.
But, it's a somewhat complicated modification to make since you have to alter your hydraulic plumbing, plus the cost of the valve itself. But a certain type of person could DIY it and have it end up cheaper than replacing a loader valve which is probably $350-1000+. But the loader valve is 'plug and play' as long as you can install everything to the correct ports, tighten properly and not mess up any threads in the process. Me personally.. I would probably 'park it a certain way' like you're talking about, and just live with it. But i did buy a double pilot operated check valve for $50 because it was listed incorrectly, so maybe i'll futz with that someday! I have heard that some loader valves have that functionality built into them, but i'm not sure i'd know how to spot it unless it was spelled out in the item description.
In a way i was lucky enough to be able to 'feel out' this whole thing about the directional lip seal in real life on my own tractor. Im an ASE master tech and i've messed with a bunch of automotive hydraulics (automatic transmissions, power steering, brake systems, fuel systems blah blah) but on one of my tractors I had a leaking gland seal on my bucket cyl and was able to 'verify' the theories in action.. If i extended the cylinder very slowly, almost nothing would come out of the leaky gland seal because i wasn't pushing fluid any faster than it could flow out of the hose port and no significant pressure was building from the 'restriction' of the return circuit (through cylinder port, through hose, through loader valve, through another hose etc). If i extended a little faster it would GUSH out of the gland seal because i was pushing fluid faster and pressure in that rod end rose enough to push fluid past the seal, but not high enough to SEAL the seal! And if i pushed the loader valve all the way and extended the cylinder 'full speed' i'd get an initial spurt of fluid as pressure in the rod end rapidly built up and then it would almost stop leaking entirely because the pressure was making the seal 'seal better' as long as it had that pressure behind it. And it all makes perfect sense. It's hard to grasp that <15psi difference can cause a leak in one direction and >1500 psi won't leak in the other direction, but in reality our gland seals don't seal that well without pressure, and noone is really 'forced' to learn that as long as the pressure their gland can seal, goes up faster than the fluid pressure does! We may all be running tractors that at any given time can only seal ONE psi more than what they've got pushing on them, but as long as those numbers move up and down together and never cross, we'd never know... we only find out when the two numbers cross.
But, it's a somewhat complicated modification to make since you have to alter your hydraulic plumbing, plus the cost of the valve itself. But a certain type of person could DIY it and have it end up cheaper than replacing a loader valve which is probably $350-1000+. But the loader valve is 'plug and play' as long as you can install everything to the correct ports, tighten properly and not mess up any threads in the process. Me personally.. I would probably 'park it a certain way' like you're talking about, and just live with it. But i did buy a double pilot operated check valve for $50 because it was listed incorrectly, so maybe i'll futz with that someday! I have heard that some loader valves have that functionality built into them, but i'm not sure i'd know how to spot it unless it was spelled out in the item description.
In a way i was lucky enough to be able to 'feel out' this whole thing about the directional lip seal in real life on my own tractor. Im an ASE master tech and i've messed with a bunch of automotive hydraulics (automatic transmissions, power steering, brake systems, fuel systems blah blah) but on one of my tractors I had a leaking gland seal on my bucket cyl and was able to 'verify' the theories in action.. If i extended the cylinder very slowly, almost nothing would come out of the leaky gland seal because i wasn't pushing fluid any faster than it could flow out of the hose port and no significant pressure was building from the 'restriction' of the return circuit (through cylinder port, through hose, through loader valve, through another hose etc). If i extended a little faster it would GUSH out of the gland seal because i was pushing fluid faster and pressure in that rod end rose enough to push fluid past the seal, but not high enough to SEAL the seal! And if i pushed the loader valve all the way and extended the cylinder 'full speed' i'd get an initial spurt of fluid as pressure in the rod end rapidly built up and then it would almost stop leaking entirely because the pressure was making the seal 'seal better' as long as it had that pressure behind it. And it all makes perfect sense. It's hard to grasp that <15psi difference can cause a leak in one direction and >1500 psi won't leak in the other direction, but in reality our gland seals don't seal that well without pressure, and noone is really 'forced' to learn that as long as the pressure their gland can seal, goes up faster than the fluid pressure does! We may all be running tractors that at any given time can only seal ONE psi more than what they've got pushing on them, but as long as those numbers move up and down together and never cross, we'd never know... we only find out when the two numbers cross.
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