Tech Briefs Magazine - August 2021 - MD-7

Prerequisites for implementing pneumatic
design best practices are an understanding
of pneumatic circuit symbols;
types of valves available such as 2-way, 3way,
and 4-way; pneumatic cylinders; and
related pneumatic components such as
tubes, hoses, flow controls, and air
preparation devices.
The starting point for a good pneumatic
design is ensuring proper plant
supply air pressure. A consistent plant
air pressure and flow is needed for pneumatic
devices to operate consistently and
reliably. Air preparation of the plant
supply at the machine is important as
well and is the first basic pneumatic circuit
discussed below.
To help control the air and the related
motion of pneumatic actuators, the
cylinder should not be oversized, as this
may cause it to stroke slowly due to
excess airflow requirements. A properly
sized cylinder provides more efficient
use of air and moves at a higher speed. A
good design will include the use of flow
controls to throttle the air exiting the
cylinder, which slows down the cylinder
motion - generally a desired outcome.
The use of cylinders with built-in cushions
also helps stop the cylinder at the
end of travel. Both the flow control and
cushions can help prevent banging and
possible damage to the cylinder.
Actuators that move too quickly can
cause excessive noise, as can the ex -
hausting of air from valves. Using mufflers
on the exhaust ports is a simple
design practice that should always be followed
to attenuate this noise.
Air Preparation Subsystem
In terms of airflow, the first pneumatic
circuit applied in most machines is air
preparation. Plant-supplied compressed
air needs to be prepped before it feeds
air to any other pneumatic circuits on a
machine. The air preparation circuit
shown in Figure 1 starts with a singlepoint
pneumatic air connection, with its
common components listed in Table 2.
These devices often include a filter, regulator,
and less often, a lubricator (FRL).
The order of the pneumatic devices
listed in Table 2 is typically the order the
devices are assembled in an air preparation
unit but not always. For example,
some designs require a manual shutoff
relief valve (VLV01) or a pneumatic isolation/lockout
valve to be the first component
connected to the plant air supply.
Others believe it should be mounted
after an FRL to ensure clean, dry air
flows through the valve.
This valve's purpose is to remove or
dump all the compressed air from the
machine. Releasing the air by rotating a
manual valve or a push-pull action de -
pressurizes the machine for maintenance
and although not shown in Figure
1, this manual valve should be lockable
in the OFF position.
Mounting this shutoff valve upstream
of the FRL enables maintenance of the
FRL at the machine. Without it up -
stream of the FRL, filter maintenance
would be difficult and could affect other
equipment in the area when air is
dumped for service. Additional plant
level, area, or zone air preparation and
shutoff units can help protect the shutoff
valve at the machine if necessary.
Motion Design, August 2021
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Tech Briefs Magazine - August 2021

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