3/2 directional seat valve
General
The directional valve of the M-.SEW type is a directional seat valve with solenoid actuation. It controls the start, stop and direction of flow.
It basically comprises a housing (1), the solenoid (2), the hardened valve system (3) and the spool (8) as closing element.
Basic principle
In the initial position, the control spool (8) is pressed onto the seat by the spring (9) and in spool position by the solenoid (2). The force of the solenoid (2) acts via the angled lever (6) and the ball (7) on the spool (8) that is sealed on two sides. The chamber between the two sealing elements is connected to port P. Therefore, the valve system (3) is pressure-compensated in relation to the actuating forces (solenoid or return spring). Therefore, the valves can be used up to 630 bar.
Notice!

3/2-directional seat valves feature “negative spool overlap”. Therefore, port T must always be connected. That means that during the switching process – from the starting of the opening of one valve seat to the closing of the other valve seat – ports P–A–T are connected with each other. However, this process takes place within such a period of time that it is irrelevant in nearly all cases of use.

The manual override (10) allows for the switching of the valve without solenoid energization.

Attention!
It is to be ensured that the maximum flow indicated is not exceeded! If applicable, a throttle insert for flow limitation is to be inserted (see functional description).
The seat arrangement offers the following options:
Control spool symbol “U“
Control spool symbol “C”
Type M-3SEW 10 U…
4/2 directional seat valve
With a sandwich plate, the Plus-1 plate, under the 3/2 directional seat valve, the function of a 4/2 directional seat valve is achieved.
Function of the Plus-1 plate:
Initial position
The main valve is not operated. The spring (9) holds the ball (4) on the seat (11). Port P is blocked and A is connected to T. Apart from that, one control line is connected from A to the large area of the control spool (12), which is thus unloaded to the tank. The pressure applied via P now pushes the ball (13) onto the seat (14). Now, P is connected to B, and A to T.
Transition position:
When the main valve is actuated, the spool (8) is shifted against the spring (9) and pressed onto the seat (15). During this, port T is blocked, while P, A, and B are briefly connected to each other.
Spool position:
P is connected to A. As the pump pressure acts via A on the large area of the control spool (12), the ball (13) is pressed onto the seat (16). Thus, B is connected to T, and P to A. The ball (13) in the Plus-1 plate has a “positive spool overlap”.
Attention!
In order to avoid pressure intensification when using differential cylinders, the annulus area of the cylinder must be connected at A.
The use of the Plus-1 plate and the seat arrangement offer the following options:
Control spool symbol “D”
Control spool symbol “Y”
Type M-4SEW 10 Y…
Throttle insert
The use of a throttle insert is required if, due to prevailing operating conditions, flows which exceed the performance limit of the valve can occur during the switching processes.
Examples:

Accumulator operation,

use as pilot control valve with internal pilot fluid tapping.

3/2 directional seat valve (see functional description)
The throttle insert is inserted into port P of the seat valve.
4/2 directional seat valve (see functional description)
The throttle insert is inserted into port P of the Plus-1 plate.
Check valve insert
The check valve insert allows a free flow from P to A and closes A to P in a leak-free form.
3/2 directional seat valve (see functional description)
The check valve insert is inserted into port P of the seat valve.
4/2 directional seat valve (see functional description)
The check valve insert is inserted into port P of the Plus-1 plate.