In a previous RealPars video,
we learned about what a spool valve is
and how it works mechanically.
If you want to watch that video,
we have provided the link to that in the description area.
In this video, we will continue this theme
and learn about how a spool valve is represented in engineering and manufacturers drawings,
how to understand what the drawing means
and how it relates to the operation of a valve.
At RealPars, we love helping you learn,
so if you enjoy this video as much as we enjoyed making it,
click the ‘Like’ button.
Subscribe and click the ‘Bell’
and you’ll receive notifications of new RealPars videos,
so you’ll never miss another one!
As we already know directional air valves, in particular, spool valves,
are the building blocks of pneumatic control.
In engineering drawings,
pneumatic circuit symbols provide detailed information about the valve they represent.
Symbols show the methods of actuation,
the number of positions,
the flow paths and the number of ports a valve has.
When we see a valve schematic,
we can see it is made up of boxes,
each containing a number of lines and arrows.
The number of boxes that make up a valve symbol
indicates the number of possible positions the valve has
Flow direction is indicated by the arrows in each box.
These arrows represent the flow path the valve provides
when it is in each position.
To the left and right of the boxes,
we can see the types of actuators being used;
In some cases, there will be a single actuator at one end of the boxes
and a spring return at the other end.
In other cases, there may be an actuator at both ends.
Let's look at an example of a typical two-position valve schematic.
This valve is controlled by a manual lever
and has a spring that returns the valve back to the start position
when the lever is not being operated.
The current state of the valve is shown by the box immediately next to the active actuator.
So in the case of our example,
if the lever on the left is NOT operated,
the spring return actuator on the right side
is controlling the valve.
So we can look at the blue box to see the flow path
and ignore the red box.
When the lever is actuated, the red box next to the lever shows the flow path of the valve
so we can now look at this and ignore the blue box.
Remember a valve can only be in one position at a given time
and the number of the boxes in its schematic
represents the number of the positions it can be in.
So in this example, the valve has two positions.
Now, let's look at a 3-position valve.
This 3-position valve has both solenoids
AND spring return actuators on both sides of the valve,
the spring return actuators will return the valve to the middle position
but only IF neither of the solenoids is active.
In this example, the middlebox indicates that there will be no airflow at all
until one of the two actuators is active.
It should be noted that colors are used in this video
only to assist with learning.
In practice, the schematics you see on a day to day basis
will not have any colors.
A typical use for the type of valve would be to “bump” or “inch” a cylinder incrementally
along its stroke length by pulsing one of the actuators.
The number of ports a valve has
is shown by the number of endpoints in a given box.
We should only count the ports in a single box once per symbol.
For example, in the 3-position valve,
there are three boxes which show the three possible positions,
but the valve has five physical ports.
So the valve will be called a 5/3 solenoid valve.
You may also see some manufacturers use letters instead of numbers to identify the ports,
but once you understand the schematic it is easy to translate this.
In this video, we have continued our theme
looking at the construction and operation of spool valves.
We have looked at how valves are represented in engineering and manufacturers drawings
and also how to translate those schematics into real-world valve operation.
We know that each position of a valve is represented by a box
which shows the physical ports and the direction of flow.
We understand where the actuators are shown in the schematic
and if we want to see valves current status
we need only to look at the box directly next to the currently active actuator.
Some 3-position valves can have a middle position
which will be active when neither solenoid is active.
Finally, we discussed port numbering
and how some manufacturers may use letters instead of numbers.
We hope you enjoyed this short video on reading pneumatic valves’ schematics.
If you’d like to learn more about any of the topics covered in this video
head over to our website at Realpars.com.
We’d love to hear your suggestions for topics you want our team to cover.
Want to learn PLC programming in an easy to understand format
and take your career to the next level?
Head on over to realpars.com