NH 7308 Loader - Replaced bucket roll hose, now bucket droops down. Won't stay in a fixed position.

[ntxguru]

Rubber hydraulic line cracked open, replaced it with new one made up at local supplier. Now the bucket will not stay in a fixed position. Tried rolling the bucket from one limit to the other with no change. I assume there must be air in the system somewhere but don't know how to bleed it.

 

[Tinhack]

Welcome to the Forum!

Without knowing more history about the problem, I would check the level of your hydraulic fluid. And be sure to run ALL cylinders through their limits.

 

[seville009]

Generally the hydraulics should be self bleeding; cycling it a few times should do it.

After you check the fluid level as suggested above, make sure the new hose isn’t leaking at the connections.

 

[LD1]

IF the problem wasnt there before and all you did was replace a hose.....cycle it some more. But dont just cycle back and forth.....go to the limit when the bucket stops moving.....and hold the lever there for 3-5 seconds.......then do the same the other direction.

I would also question what caused the line to "crack" open. Was it just age? or did you do something to damage the cylinder before the line blew and you have other problems

 

[Vigo327]

Nothing moves between the valve and the cylinder when the relief valve is open at the end of a cylinder stroke. Fluid simply enters the valve, exits the relief, and nothing between the work ports and cylinder moves.

But, you do need to hit the ends of travel and hit high pressure, you just dont need to leave it there for any length of time. The reason you need to hit high pressure is because if you have an air pocket in the cyl, it acts like a spring. Compressing it to a high pressure is what is going to ‘propel’ it out of the port when you switch directions on the valve and let that side of the cylinder ‘decompress’ (nothing decompresses but the air).

Hitting the ends of travel will minimize the volume of air in the cylinder, but if you dont also build up any pressure once you hit the end, then unless the cylinder port happens to be at the highest point and the remaining air works its way out like bubbles in water, it would have no real motivation to move towards the exit. If you compress it to 1500psi (or whatever) and then make the port on the cylinder a 0 psi exit hole (not zero in real life, but for sake of argument) then the air will launch itself in that direction.

So do more back and forth, and make sure you make pressure at the end of stroke. Whether you hit relief pressure for half a second or 10 seconds it will accomplish the goal.

 

[LD1]

IF you hit the end of the travel...IF there is air in the cylinder it wont go into relief and will force out the air.

If you stop immediately after movement stops, it wont purge the air as effectively.