The symbol is representative of the mechanics. The 4/3 directional valve means that the block has 4 holes and the spool (item 7) 3 positions.
The spool moves when the coils are energized (items 5 and 6). It resumes its initial position thanks to the return springs (items 10 and 11) located on each side of the spool.
At rest the spool is closed (P, T, A, B closed).
- P : Pressure.
- T : Tank.
- A & B: Directional valve outlets
The pump (item 1) driven by a heat engine (item 2) delivers 30l / min which are directed towards the tank by raising the pressure relief valve (item 3) at a pressure of 200 bars.
The cylinder ports A and B are closed and lock the cylinder in position.
To note : Directional valves spool are not waterproof. Despite a closed spool, it is possible that a slight leak appears between P to A & B thus causing drift of the cylinder if it is not loaded.
3- Directional valve 4/3 closed center: straight arrows