* Emergency stop: see chapter 2.1
17
Fig. 4-12
Fig. 4-13
4.10
HYDRAULIC SYSTEM WITH OPEN OR CLOSED CENTRE
(See also section 14.1.)
The selective control valve (V1) allows you to choose between an open and closed centre for the
hydraulic system. Most tractors have a hydraulic pump which produces a fixed volume of oil per
revolution (open centre). The valve must then be in the open position. (See fig. 4-12.)
Some other tractors (such as John Deere) have oil pumps with
variable
volume per revolution
(closed centre). The valve must then be in the closed position. (See fig. 4-13.)