hydraulic?

Do most or all tractor hydraulic systems have a vent or are they sealed? I asked this before but asked about ih2500 and did not get an answer. THANKS DAN

All systems that I know of are vented.
Usually at the tank.

Some are, others aren't. Most probably are. Depends on the design of the specific system.

The super A and 140s arent vented. They build up a bit of presure in their system.

There are vented and non vented systems. In systems that have large capacity there is almost always a vent, in self contained systems with no remotes, there may not be.
One way cylinders, with no hose on the non pressure end, and a vent, or atmospheric port, draw their extend volume from the reservoir. This volume is substantial, and would lead to a vacuum in the system, and cavitation in the pump if allowed to happen with no reservoir vent. Generally all one way cylinder systems need vents unless the non pressure end of the cylinder is plumbed into the reservoir, acting as additional volume, and returning fluid to the res as it is being pumped out to the pressure side. The ram of the cylinder takes up volume in the system, so there is somewhat less returning than is sent. In a large complex system this differential in volume can be a problem if all cylinders are extended at the same time. Venting is good but it also provides the primary route for moisture to get into the system. A vent filter with a desiccant is probably best. Systems that routinely operate at full temperature under load heat the water out of the oil. Systems that are worked only lightly will need the fluid changes as it becomes milky. Heating the fluid can drive out the moisture, but care must be taken to prevent flash fires. JimN

I can'r speak with any authority on this but I don't think the Cub Touch Control system is vented. If that is true, the same probably applies to the system on an A or Super A.