 |
|
Since one valve will normally cost less than two, circuit designers will opt for a single 5/2 or 4/2 solenoid valve to operate the double acting air actuator.
The 5/2 configured compressed air valve works the same way as the 4/2 style.
The 5/2 valve will have two actuator ports that are plumbed to the air actuator (air cylinder). When compressed air is supplied to the 5/2 valve, that air will pass through the valve and air will flow to just one of the two actuator ports.
The other actuator port will be open to exhaust allowing air from one side of the air actuator to escape, as a fresh compressed air supply flows into the other cylinder port.
 |
When the 5/2 valve is shifted, the spool or poppet inside the valve moves, and air is directed to the other actuator port. Then the previously charged line is opened to atmosphere allowing it to become the exhaust line from the actuator.
In this manner, the actuator can be extended or retracted alternatively; hence the term double acting.
The ‘home’ position for the actuator (whether it's an extended or retracted rod or, if a rotary actuator, rotated in one direction or the other) will be determined by the requirements of the application.
The 5/2 valve will be plumbed to ensure that air is supplied to the appropriate actuator port when the air valve is at rest based on the demands of that particular air circuit.
We know that the first number in a valve number designation refers to the number of ports, and the second number is the number of positions. Therefore, a 5/2 air valve will have five ports and two positions.
Two of the ports are for the actuator supply as noted above, one of the ports will be the supply air to the valve, and the other two – and this is the difference between the 4/2 and 5/2 – the other two will be exhaust ports. A 4/2 has one exhaust port, but the 5/2 valve has two exhaust ports.
The additional exhaust port provides significant benefit to the system designer, and that’s why, in selecting a valve for a double acting actuator, I would always opt for a 5/2 version over a 4/2.
Having two exhaust ports allows the installation of two exhaust flow controls , one for each exhaust port.
For an air operated rotary actuator, the two speed controls can adjust speed of rotation in one direction and allow a different speed for rotation in the other.
A 4/2 valve, with it’s single exhaust port, can only provide one speed adjustment which will affect the actuator similarly in both extend and retract.
Depending on the manufacturer and their design of their 5/2 valve, you may be able to use the two exhaust ports as dual supply ports, and use what was the supply port as a common exhaust.
Plumbing the 5/2 valve with supply air to the two exhaust ports does negate the dual flow control possibility for that valve. However, now with the two supply lines, two separate pressures can be sent through one 5/2 valve to allow different forces to be generated by the cylinder in the extend or retract cycle.
If the application for a particular actuator means that it is moving without load in one or the other direction, lowering the pressure for that movement can save significant dollars in reduced compressed air use.
If it’s your job to select a valve for a double acting cylinder application, picking the 5/2 over the 4/2 provides some benefits, all other things being equal.
Interested in learning how to draw a 5/2 air valve? Just click click here!
Want to know all about 5/3 valves? Click here.
To top
