The Friends of Ferguson Heritage Ltd. - The Ferguson Hydraulic System
We all know what an immense change the three point linkage
made to mechanized farming, allowing the use of mounted
implements.Fifty-odd years later, many of us (me included) are
still trying to work out just how it all works. Well, here's my
There's a lot of bits in there, but I've
ignored most of them, simplified the rest, and then taken
liberties with parts such as the pump and the control valve. I've
also painted the external components in the wrong shade of grey,
and dyed the tractor oil yellow...
Control spring: this
is the big spring which the top link is connected to.
When the implement (e.g. plough) meets with more
resistance (in the soil), it pivots around the lower
links, and puts pressure on this spring via the top link
Lift arms: er, the
arms which do the lifting... (shrug)..
Pump: not drawn in
Control valve: this
is difficult to represent in two dimensions, so it has
been "re-designed" here- don't attempt repair
of your tractor using this diagram... The valve has three
Forward: (toward the front of the tractor) oil is
allowed into the pump, and then forced into the
ram. The oil path through the control valve is via a hollow annulus around the spool.
Middle: no action: no oil movement.
Rear: oil is cut off from the pump inlet; oil is allowed to drain out of the ram,
lowering the lift arms.
Don't skip over this bit:
that's where I went wrong. The important bit about the
fork assembly is that it pivots around the point marked
"a", which is mounted on a link connected to
the top link. It also has a "knee" at the point
marked "b". The "knee" is normally
held straight by the fork retracting spring. At
the top of the fork assembly is a "shoe" which
is pushed forward when you push the control lever down.
The following pages will be slower to download (image size is 44 and 33 kb)
Hydraulic Lift shows the action
when an implement is raised and lowered.
Safety Device. Well named: before Ferguson,
tractors tried to invert themselves (with driver) when a buried
obstruction was met. More information
on the safety device soon, if any interest is shown....
The author would like to acknowledge Johan Bakker, of the USA, and John Gaunt, of Australia, for their comments and assistance in things hydraulic.