Air seeping into rod seals?

   / Air seeping into rod seals? #1  

SmallChange

Platinum Member
Joined
Apr 19, 2019
Messages
668
Tractor
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)
My FEL always seems loose and floppy, and if I move things around a lot with the tractor leaning forwards and also backwards, it all tightens up. But soon it's back the same way.

I'm wondering if the problem is that the bucket cylinders generally wind up loaded in compression when I park, because of how the bucket sits. If it's been parked a week or so, the bucket winds up curled, even though it was horizontal when I parked. I'm not sure what's happening to the hydraulic fluid on the closed end of the cylinder, but, could it be that on the rod end of the cylinder, air is coming in around the rod seal? That side of the cylinder is under some vacuum as the whole setup relaxes over time, and the rod seals obviously can seal against huge pressures when the fluid behind them is under pressure with the cylinder in tension. But if the cylinder's being compressed, isn't it easy for air to slowly seep through those seals?

I'm going to try some experiments, but I'm packing for a trip at the moment and so can't do anything with it for a few days. Wondered if anybody had any advice.

Thanks!
 
   / Air seeping into rod seals? #2  
The best I can offer is, don't worry about it.

They all curl up like that.
 
   / Air seeping into rod seals? #3  
My FEL always seems loose and floppy, and if I move things around a lot with the tractor leaning forwards and also backwards, it all tightens up. But soon it's back the same way.

I'm wondering if the problem is that the bucket cylinders generally wind up loaded in compression when I park, because of how the bucket sits. If it's been parked a week or so, the bucket winds up curled, even though it was horizontal when I parked. I'm not sure what's happening to the hydraulic fluid on the closed end of the cylinder, but, could it be that on the rod end of the cylinder, air is coming in around the rod seal? That side of the cylinder is under some vacuum as the whole setup relaxes over time, and the rod seals obviously can seal against huge pressures when the fluid behind them is under pressure with the cylinder in tension. But if the cylinder's being compressed, isn't it easy for air to slowly seep through those seals?

I'm going to try some experiments, but I'm packing for a trip at the moment and so can't do anything with it for a few days. Wondered if anybody had any advice.

Thanks!

It is always advisable to relieve all pressure from your hydraulic lines and cylinders after you shut down your machine. This helps to prolong seal and control valve life. Simply activate the control valves until the implement achieves it's natural resting point with the engine off.
 
Last edited:
   / Air seeping into rod seals? #4  
I try to park my tractor so the cylinders are all retracted to prevent dust on the exposed rods. I do like the idea of relieving pressure after killing engine, though.
 
   / Air seeping into rod seals? #5  
I try to park my tractor so the cylinders are all retracted to prevent dust on the exposed rods. I do like the idea of relieving pressure after killing engine, though.
You make a valid point Roadworthy. Most of my equipment is under roof and therefore having the rods exposed has not been a problem for me so far. If it were stored outdoors I would tend to lean towards keeping the rods in the cylinders as well. Perhaps propping something underneath them so they can be at rest while at the same time being retracted.
 
   / Air seeping into rod seals? #6  
Smallchange, in my opinion you’ve found your way to a fairly ‘advanced’ little nugget of information that a lot of very knowledgeable people claim is impossible or wrong.

I think you’re exactly correct. In the absence of something that seals better than a loader valve, like a ‘load holding valve’ or ‘double pilot operated check valve’, then yes the oil in the base end can gradually seep past closed loader valve to tank port, and rod end of cylinder can gradually suck air past gland seal that doesnt actually seal all that well with no pressure behind it because it’s a directional lip seal.

I think most people that have this happen simply dont notice. If you have a column of air in the rod end of the curl cylinders, bucket may still keep its angle when you lift the loader arms because the base end CAN hold negative pressure to a greater extent than the rod end, so if the bucket is empty and light enough it might not present an immediate symptom (drooping). Now if it did drop and one tried to curl the bucket, there would be a slight delay while the hydraulic system compressed the air column as it ‘refilled’ the rod end with fluid. Depending on how much pressure you get the rod end up to, the air column will shrink to a miniscule proportion of its original volume, but it will still be there because it will be sitting at the top up against the piston and the only way out is the fluid port all the way down by the gland. Depending on how much pressure you built in that circuit before releasing the valve, you’d have a varying degree of ‘springiness’ in the bucket’s downward/dump direction because the compressed air acts like a spring. If you only added enough pressure to hold the bucket at level after it had initialy drooped, you may see it ‘bouncing’ over bumps. But if you held the valve all the way until the bucket was fully curled and hit relief pressure, then at that pressure the air column would be so tiny, that any bouncing you might experience from severe jolts would hardly be visible or noticeable. The entire rod end of the cylinder worth of air, raised to 1700-2500psi or something like that, would probably be a 1/4” thick layer of air hugging the bottom of the piston. At most youd get less than that of bounce, and not notice anything. But the air would remain in the cylinder until you either fully dumped the bucket, raised loader to full height and put the rod end port near level or above the piston, or cycled the cylinder up and down multiple times. Eventually the air would end up ‘purged’ in the tank. But the issue would reoccur consistently as long as you parked it the same way for the same amount of time.

But if you did something like park the bucket on top of something that was only touching the very rear of the bucket, the weight of the bucket would be trying to extend the cylinder, would put a small amount of pressure on the gland seal, and then if the bucket EVER dropped while parked like that, it would be purely from the leakage between the shuttle valves and their bores in the loader valve assembly, but there would be no air added to the system and it would have full normal ‘stiffness’ in both directions the instant you started it.

👍
 
Last edited:
   / Air seeping into rod seals?
  • Thread Starter
#7  
But if you did something like park the bucket on top of something that was only touching the very rear of the bucket, the weight of the bucket would be trying to extend the cylinder, would put a small amount of pressure on the gland seal, and then if the bucket EVER dropped while parked like that, it would be purely from the leakage between the shuttle valves and their bores in the loader valve assembly, but there would be no air added to the system and it would have full normal ‘stiffness’ in both directions the instant you started it.
Thank you! THIS is the direction I was trying to get to!

To clarify, I didn't say so before, but I thought of the bucket curling up while parked as a clue, not a problem itself. I don't care if it does that, but it's a clue that the reason I have so much sloppy operation is air seeping in.

I'm going to find something to park on such that the bucket droops into the dump position rather than the curl position. I also want to make sure that if there's any force acting on the lift arms, it's trying to extend the cylinders too, not to compress them. It might mean that I push the loader down to lift the front end slightly when parking, just enough to unload the front tires (and not so much that anything can crawl under them for a nap).

No pressure would be best, but positive pressure would be much better than negative, in the rod ends of the cylinders.
 
   / Air seeping into rod seals?
  • Thread Starter
#8  
It is always advisable to relieve all pressure from your hydraulic lines and cylinders after you shut down your machine. This helps to prolong seal and control valve life. Simply activate the control valves until the implement achieves it's natural resting point with the engine off.
Seems like the bucket motion valve would need a float position to do this on the bucket cylinders, no?
 
   / Air seeping into rod seals? #9  
My FEL always seems loose and floppy, and if I move things around a lot with the tractor leaning forwards and also backwards, it all tightens up. But soon it's back the same way.

I'm wondering if the problem is that the bucket cylinders generally wind up loaded in compression when I park, because of how the bucket sits. If it's been parked a week or so, the bucket winds up curled, even though it was horizontal when I parked. I'm not sure what's happening to the hydraulic fluid on the closed end of the cylinder, but, could it be that on the rod end of the cylinder, air is coming in around the rod seal? That side of the cylinder is under some vacuum as the whole setup relaxes over time, and the rod seals obviously can seal against huge pressures when the fluid behind them is under pressure with the cylinder in tension. But if the cylinder's being compressed, isn't it easy for air to slowly seep through those seals?

I'm going to try some experiments, but I'm packing for a trip at the moment and so can't do anything with it for a few days. Wondered if anybody had any advice.

Thanks!
Always to remember the last thing you do, just before dismounting the tractor is to cycle the loader control lever through all positions. This will relieve all residual hydraulics pressures in the loader hydraulic system.
 
   / Air seeping into rod seals? #10  
Seems like the bucket motion valve would need a float position to do this on the bucket cylinders, no?

I believe this should be possible with any open center hydraulic system with the engine turned off. My tractor has a joystick for the controls and I simply activate the valve to lower the arms and then at the same time cycle left to right to drop or curl the bucket depending on it's position and hold there until it stops moving. Then as a final step make clockwise and counter clockwise motions to activate all the valves.

I hope this helps!!
 
Last edited:
 
Top