How to Read a Spool Valve Schematic Drawing

How to Read a Spool Valve Schematic Drawing


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

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