Thanks Scotty. That is very interesting.
What is a hydraulic circuit? Do you mean just draw all the hydraulic line connections and where they connect to?
A hydraulic circuit is just hydraulic-speak for a fluid pathway. The simplest non-work pathway is when your tractor is just sitting there running but not doing anything. Fluid is moving from the reservoir thru a filter, to a pump, past a control valve (closed), and back to the reservoir. That would be a hydraulic circuit NOT doing any work.
To do work, the path back to the reservoir is blocked which builds pressure in the whole system and the cylinder moves. That would be a hydrualic circuit doing work.
Yes, drawing those parts, hoses, and connections is exactly what I'm suggesting. It sounds to me like you want to figure this out, and a good first step is to draw out as much as you can. Most of the common compact & utility size tractors have a similar hydraulic circuit. Once you understand one of them, they are all just variations on the same theme.
Here is more detail on how the simplest of all tractor hydraulic works when the hydraulics are NOT doing any work:
From the hydraulic reservoir or tank - usually shared with the transmission - hydraulic fluid is sucked through a filter and into the hydraulic pump. At that point it has very little pressure. The hydraulic pump then circulates the fluid through all parts of the system until ultimately returning the fluid home to the hydraulic reservoir. There is fluid flowing all through the system, but it isn't doing anything. Just flowing around a circle in which there no high pressure.
To get the hydraulic flow to build pressure and do some work for us - like moving a cylinder rod - all we have to do is to block off that easy flow of hydraulic fluid back to the reservoir.
Here is how it works:
The operator moves a control valve lever which diverts a flow of fluid to a cylinder or set of cylinders while simultaneously closing off that easy return path back to the hydraulic reservoir. Now the fluid is still being pushed by the pump, but since its low resistance path back home to the reservoir has been blocked the pump keeps pushing fluid and builds up pressure until something gives - in this case the "something that gives" is that the cylinder rods all move a little which allows more fluid to enter the cylinder.
Once the operator decides that the cylinder rod has moved enough, he releases the control valve lever, trapping the additional fluid in the cylinder and simultaneously re-opening the old easy return pathway back to the reservoir.
That's about all there is to it. The downside of this simplest of all open center type hydraulic flow system is that it is only good at doing one thing at a time. After the fluid exits the pump as flowing fluid, all of the various hydraulic systems are receiving that fluid in parallel with one another - but only one can work at a time. The control valve levers select which system this will be.
One system (for example the FEL lift cylinders is one system) can receive flow, build pressure, and do some work, but it can only do so by simultaneously blocking the flow into and out of all the other parallel systems.
Bottom line is that somehow in your tractor two of these circuits - the curl and the 3pt - have gotten connected in series instead of parallel. Instead of curl & 3pt being on separate parallel branches, their flow is in line with each other. That may or may not have been the way it was intended to work. Drawing out a diagram of the system is the only way I know to figure it out, but maybe this rather long-winded explanation will help too.
Hope this helps,
rScotty
Appreciate your help.
