Air often enters the hydraulics when the lines are replaced or if the cylinder is new. The hydraulic cylinders in most newer models of tractors are self-bleeding. There is a check valve inside the cylinder, and any air is expelled through an overflow system. Running the cylinders through their range of movement should expel the trapped air. If you operate an older model, however, and you are experiencing poor performance in the hydraulics, you may have to bleed the air out of the hydraulic cylinder manually.
Remove the filler nut from the cylinder with the adjustable wrench. Refer to the owner's manual to locate the nut, if necessary. Fill the cylinder with hydraulic fluid. Reinsert the filler nut and tighten it.
Extend the hydraulic cylinder. For example, if it runs a front-end loader, raise the bucket.
Find the bleeder nut and loosen it. If it can't be turned by hand, use the adjustable wrench.
Allow the hydraulic fluid to discharge from the bleeder nut. Once there is no air present in the liquid being emitted, tighten the nut.
Operate the cylinder to check that it functions properly. For example, start the engine and raise the bucket of a front-end loader.
If you disconnect hydraulic lines, cap them off. This reduces the amount of air that may enter the cylinder. If you must bleed air from a cylinder, it may be a good time to change the hydraulic fluid if it has not been done recently.
Do not bleed the cylinder after the tractor has been running for a while as the cylinder and the hydraulic fluid may be hot.