Direction control valve and reversing circuit

The directional control valve can be divided into one-way control valve and reversing control valve according to the action direction of air flow in the valve.

(1) One way control valve

1) Check valve.

The working principle and function of pneumatic check valve is the same as that of hydraulic check valve.

In the pneumatic system, in order to prevent the compressed air in the air tank from flowing back to the air compressor, a check valve is installed between the air compressor and the air tank. The one-way valve can also be combined with other valves to form one-way throttle valve, one-way sequence valve, etc.

2) Shuttle valve (or gate valve). Shuttle valve is a combination valve with two check valves in reverse series. Because the valve core moves back and forth like a weaving shuttle, it is called shuttle valve.

Its working principle is that when P1 enters the air, the valve core is pushed to the right, P2 is closed, so the air flows from P1 into chamber a, as shown in Fig. 3-25 (b);

On the contrary, when the valve core is pushed to the left from P2, the air flows into P2 cavity from several sides, as shown in Fig. 3-25 (c). When P1 and P2 are fed at the same time, which end has high pressure, a will connect with which end, and the other end will automatically close. It can be seen that as long as there is one input in the two output population of the valve, there is output at the output port, and the relationship between input and output presents a logical "or".

Or gate shuttle valve is widely used in logic circuit and program control circuit. Through the function of shuttle valve, solenoid valve and manual valve can operate cylinder independently.

3) Figure 3-27 shows the working principle of the dual pressure valve.

When P1 is in air, push the valve core to the right end, and a has no output, as shown in Fig. 3-27 (a); When P2 is in air, push the valve core to the left end, and a has no output, as shown in Fig. 3-27 (b); Only when P1 and P2 are simultaneously air fed, a has output, as shown in Fig. 3-27 (c); When the P1 and P2 gas pressures are not equal, the low air pressure is output through a.

Thus, the valve only has output when a is simultaneously fed in two transmission population, and the output and the input are logically "and". The double pressure valve is widely used in interlock circuit. Only when the positioning signal 1 and clamping signal 2 of the workpiece exist simultaneously, the double pressure valve can have output, which makes the reversing valve reverse, thus feeding the cylinder.

4) Quick exhaust valve. The valve used to make the pneumatic components or devices exhaust quickly is called the quick exhaust valve, or the quick exhaust valve. Usually, when the cylinder is discharged, the gas is discharged from the cylinder through the pipeline and the exhaust port of the reversing valve. If the distance from cylinder to change-over valve is long, and the exhaust port of the reversing valve is small, the exhaust time is longer and the cylinder movement speed is slow. At this time, if the rapid exhaust valve is used, the gas in the cylinder can be discharged directly from the fast exhaust valve to the atmosphere, and the speed of the cylinder movement can be accelerated.

The experiment shows that the speed of cylinder can be improved after installing the fast valve.

When p enters the air, the diaphragm 2 is pressed down to seal the exhaust port 0, and the air flows to chamber a through the small holes around the diaphragm, and a has output, as shown in Fig. 3-29 (b); When p cavity is empty, the pressure of a cavity will lift up the diaphragm, P

It is not connected with a, a is connected with 0, and the gas in chamber a is quickly discharged to the atmosphere, as shown in Fig. 3-29 (c).