The above directional valve is a Cetup type mounting (ISO standard).
It is mounted on a drilled block and assembled with 4 screws. The seal between the drilled block and the distributor is provided by 4 O-rings.
This directional valve has 4 holes and 3 positions (4/3).
The diagram is representative of the mechanics. The spool (item 7) is represented by 3 boxes.
The central box corresponds to the spool (item 7) in the rest position. The P communicates to the T, the A & B are closed. (This center is also called tandem center)
The spool moves with 2 electric coils (items 5 & 6). Two springs (item 10 & 11) allow the spool to return to neutral (item 7). A mechanical pusher (item 8) is used to force the spool with a peg. (Used for troubleshooting).
The pump (item 1) is driven by a heat engine (item 2). It delivers a flow rate of 30 l / min which returns to the tank through the center of the directional valve, thus avoiding pass the oil in the pressure relief valve (item 3). We will read 2 bars in M1, pressure created by the pressure drops (friction of the oil in the piping).
The cylinder is hydraulically locked since the A & B holes are closed.
To note : Directional valve spools are not waterproof. If a mechanical force is permanently applied to the cylinder (suspended load for example), the cylinder may drift. It will then use pilot check valves to block the cylinder and change the center of the directional valve (use a center Y to decompress the valves).
3-Directional valve 4/3 center open from P to T: crossed arrows
