Aeration tractor fluid- How much is normal?

[J252]

Does anyone know how much hydraulic fluid aeration is normal when a tractor is operating?

I am working on the 3PH control valve on my Kubota L3400 which is inside the cylinder housing under on the seat. I removed and reinstalled this housing a couple of times which gave me a unique view of the trans sump I don't normally get. I noticed that after briefly testing and then removing the housing, the hyd fluid visible in the sump went from clear to aerated (entrained air, not water).

Is this normal or does it point to a small leak on the suction side of the system? I suppose the position control valve dumps its unloader inside the case but above the fluid level, which would seemingly cause some aeration too, right?

I ask because I am also battling a problem of power steering that eventually fades out, and I was wondering if it was possible that after an hour or so, the entire sump was getting aerated? L3400 Weak Power steering - TractorByNet.com

 

[techman]

You should not see visible aeration of the oil. Look for a suction side leak. Another possibility is worn cylinder rod seals. This can allow air to be sucked into the cylinder with certain overrunning load conditions. This air then is discharged into the system.

Don't let it go too long since a high level of entrained air can result in cavitation and damage to the pump.

paul