two position valves

TWO POSITION VALVES

1. 2/2 Directional Control Valves

The 2/2 valves have 2 ports and 2 positions.

1. Construction and Operation

The poppet-type check valve illustrated in Fig.6.10 is a typical 2/2 valve. However, the construction and operation of a similar type 2/2 DC valve is illustrated in Fig.6.1.

Position 1: When the push-button is in normal position, spring and fluid pressure force the ball up, therefore the flow is blocked, as shown in Fig.6.10(a).

Position 2: When the pressure of the push-button pushes the ball off its seat, then the flow is permitted from port P to port A, as shown in Fig.6.10(b).

2. Graphic Symbols

Fig.6.10(c) depicts the above operation of a push-button operated, spring return type 2/2 valve.

2. 3/2 Directional Control Valves

The 3/2 valves have 3 ports and 2 positions.

1. Construction and Operation

The construction and operation of a typical sliding-spool type, solenoid-actuated 3/2 DC valve is illustrated in Fig.6.11. It has three ports or openings: pressure supply port (P), output port (A), and exhaust port (R).

As shown in Fig.6.11(a) and (b), the valve is actuated by a current passing through a solenoid and, returned to its original position by a spring. The spool slides over the finely finished valve bore inside the valve housing.

Spool position 1: In the original or neutral position of the spool, (Fig.6.11(a)), the pressurized fluid flows from port P to port A to move the actuator, the exhaust port (R) remaining closed.

Spool position 2: When the solenoid is activated (Fig.6.11(b)), the spool moves to the extreme left. In the extreme spool position, the fluid from port P gets closed and hence the fluid is permitted to flow from port A to port R.

Thus the valve alternately connects and disconnects fluid supply to the cylinder by the sliding spool.

2. Graphic Symbol

Fig.6.11(c) shows a graphic symbol of a solenoid actuated, spring return 3/2 valve, illustrating the above operation.

3. 4/2 Directional Control Valves

The 4/2 valves have 4 ports and 2 distinct positions.

1. Construction and Operation

The construction and operation of a typical sliding-spool type 4/2 DC valve is illustrated in Fig.6.12. It has four ports or openings, P, A, B, and T.

Spool position 1: When the spool is in position as shown in Fig.6.12(a), the fluid can flow from port P to port A and return from port B to port T.

Spool position 2: When the spool is in the position as shown in Fig.6.12(b), the fluid can flow from port T to port A and return from port B to port P.

2. Graphic Symbol

Fig.6.12(c) represents the graphic symbol for the above 4/2 DC valve.