air in hydraulics

tank->filter->pump->spool->cyl->spool->tank

Im having trouble with air in the cylinder, causing slow response on lifting, and sudden jerky motion when letting the cyl down under load. Ive unmounted the cyl and held the ports high in an effort to get the air out to no avail.

Ive also removed the return line from the tank and run it through a section of clear hose to watch for air. during open-center operation (no levers pulled) the oil looks clean and clear, with no visible air passing through. when the cylinder is cycled down under load, large burps of air pass through the hose.

Any ideas on the culprit?

You've got the filter in the wrong place. Put it behind the system "exhaust" just before she goes back into the tank so that you get it clear away from that pressure side and the cylinder, 'cause you're starving 'er fer oil.

The filter should only work on the "open center" part of the system and not the working side.

Hope this makes sense,

Allan

Ill remove it from the circuit and test it for air. If it is successful, Ill move it to the return line.

Thanks!

res->pump->spool->cyl->spool->res

the cylinder seems to stroke fine both directions without delay until it is loaded in the extended direction. When the spool is moved to the retract position, the load drops quickly and suddenly. When the cylinder is retracted enough to fully unload it, it pauses just after the load is removed, then resumes, as though the load pushes the rod in until there is no more load, then it has to wait until the air in the cylider is compressed enough to continue retracting.

Im no professional at hydraulcs, yet no newbie either. Ive built 2 other loader systems from scratch in the past. I had air getting into the system on one previous system when the returning oil stirred up the resivoir enough to make air bubbles, but that was quickly solved. This one is baffling me.

Im considering perhaps a seal on the cylinder itself.