Bosch Rexroth R901281588

2/2 and 3/2 directional seat valve General The directional valve of the M-.SMM type is a directional seat valve with manual, mechanical operation. It controls start, stop and direction of flow and basically comprises of the housing (1), type of actuation (2), the hardened valve system (3) as well as the ball/the spool (4) as closing element. Basic principle In the initial position, the ball/the spool (4) is pressed onto the seat by the spring (7), and by the relevant type of actuation (2) in the switching position. The actuation force acts via the ball (5) on the actuating plunger (6) 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 (actuation 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 start of the opening of one valve seat to the closure of the other valve seat – ports P–A–T are connected with each other. However, this process takes place within such a short time that it is irrelevant in nearly all cases of use. 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:

2/2 directional seat valve
Symbol “P”
Initial position	P and T connected
Spool position	P blocked
Symbol “N”
Initial position	P blocked
Spool position	P and T connected

3/2 directional seat valve
Symbol “U”
Initial position	P and A connected, T blocked
Spool position	P blocked, A and T connected
Symbol “C”
Initial position	P blocked, A and T connected
Spool position	P and A connected, T blocked

Type M-2S.. 6 N… Type M-3S.. 6 U… 4/2 directional seat valve The use of the Plus-1 plate and the seat arrangement offer the following options: 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 (4.1) 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 (4.2) 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”. In order to avoid pressure intensification when using differential cylinders, the annulus area of the cylinder must be connected at A.

Symbol “D”
Symbol “Y”

Type M-4S.. 6 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.

2/2 and 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. 2/2- and 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.