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This article will give detailed information on air pressure
The article will cover the following:
Air pressure switches and pneumatic pressure switches
Applications, adjustments, and construction of an air
Types of air pressure switches
Differences between flow switches and pressure switches
Diagram of an air pressure switch circuit
Calibration of pressure switches
Components of air pressure switches
…and much more
Chapter 1: Air Pressure Switches and Pneumatic Pressure Switches
Air Pressure Switches
A mechanical device called an air pressure switch uses pressure
to regulate how an electric air compressor operates. The
device's air pressure circuit mechanism supplies the motor with
electricity. A pressure switch relief valve is a part of the
pressure switch on air compressors.
By releasing head and line pressure, this valve makes it simpler
and less complicated for the machine to start. Various air
pressure switches are available, and they all have unique
functional characteristics. Switches still function much the
same for all devices, though.
The person in charge can switch the level to auto position once
the air compressor has been connected. This act of switching
causes the motor to turn on and pressurize the compressor
simultaneously. As a result, the device's pressure system is
A diaphragm within stops the motor by severing the circuit due
to the pressure being set. The pressure relief valve
simultaneously releases back pressure. The pressure decreases to
a certain level due to the air used in the procedure. Once more,
when the connections close, the motor turns on. Up until the air
compressor is in use, this procedure continues.
The air pressure switch is utilized throughout numerous sectors
for various purposes. The air pressure switch measures the rise
and decrease in system temperature to provide electrical
Pneumatic Pressure Switches
Pneumatic pressure switches are used in pneumatic systems to
monitor changes in air pressure. They are useful for pressure
and vacuum applications and come in various forms, including
adjustable and non-adjustable devices. These tools are
frequently used to check the pressure in compressed air systems
automatically and can be employed in hydraulics and
manufacturing. When a certain pressure or setpoint is reached, a
pressure control valve known as a pneumatic pressure switch
produces an output. The pneumatic pressure switch performs its
function by delivering process pressure to a piston or diaphragm
to provide a force akin to a pre-compressed range spring. Fluid
pressure can also be detected using the pneumatic pressure
switch. A diaphragm is frequently utilized as a sensing element
in pneumatic pressure switches. To start a control action or set
off an alarm, the movement of the sensing element is employed to
actuate one or more switch connections.
Pneumatic Switches Working Principle
Pneumatic pressure switches are essentially pressure control
valves that may direct airflow in various directions. In
general, there are two different conditions to take into
account. First, the airflow to the second slot is initially
obstructed if the switch is placed in the first slot. The action
is reversed if the control is turned to the opposite setting. If
the pneumatic pressure switch is manually operated, the user
only needs to alternate between the two switches based on the
situation and the demand that is present at the time. Second, a
pneumatic pressure switch powered by electricity automatically
enables the switch or the user to choose between a broken or
open circuit and a closed circuit. This choice permits the
movement of air between two locations.
Differences Between Pneumatic Pressure Switches and Air Pressure
When water is pulled from the pressure tank, a pneumatic
pressure switch automatically switches on a water pump. When the
reservoir reaches a predetermined pressure, it turns off an
electrically powered gas compressor. When the tank reaches the
desired air pressure level, an air pressure switch, which
maintains consistent pressure, can shut off the compressor. The
switch can also activate the compressor if there is a reduction
in air pressure and more air is needed.
Chapter 2: Applications, Adjustments, and Construction of an Air
Several industrial control systems use air pressure switches and
pneumatic pressure switches. Below are some uses:
These switches are utilized in many different types of
equipment, including process equipment, HVAC equipment,
pumping systems, compressed air systems, etc.
These switch types are widely utilized in various industrial
and manufacturing applications, such as pumps and compressors.
These are utilized in manufacturing to regulate equipment,
including press, welding, and injection molding machines.
Pneumatic and hydraulic switches control truck air bellows and
train brake pressure.
These switches can be used in various automobile applications,
including power steering, transmissions, and engine oil
These switches are used in medical equipment to monitor the
pressure of incoming gases, such as oxygen supply systems.
These switches are employed in filtration systems, blockage
detection in various systems, compression units within medical
facilities, HVAC boiler room controls, medical breathing
apparatus such as ventilators, machinery in agriculture such
as crop spraying, water levels in washing machines, DNA test
machines for solution level, among other applications.
Compressed Air Systems
One should now realize the significance of the pressure switch.
If the pressure switch is not functioning properly, the
compressor function does not reach the anticipated height.
HVAC equipment is used in residential and commercial buildings
to offer heating and cooling functions. For safety reasons,
pressure switches are a part of HVAC equipment. The air pressure
switches in HVAC equipment assist in sensing the maximum and
minimum set points. The trait is seen in air conditioning
Depending on the setpoint level, the system can start or stop
using this function. Yes, there will be hassle-free HVAC
operation since the pressure switch enables an automated system
to turn on and off. However, the heating and cooling system's
performance deteriorates if the air pressure switch needs to be
The use of air pressure switches is common in the manufacturing
industry. The air pressure switch aids in the manufacturing and
industrial sectors' seamless achievement of objectives. The
pressure switch increases production efficiency in all
manufacturing sectors. Yes, the switches provide a steady flow
of gas and liquid for the systems' ongoing operation in the
The primary purpose of the air pressure switch is to maintain
the fluid level in the pumps. The pressure switch engages and
deactivates water pumps based on the specified points.
Thus, the following briefly describes a pressure switch-like
circuit, its operation, and its applications. This industrial
sensor is used to open or close an electrical contact by
detecting a fixed quantity of pressure. To actively monitor the
air pressure or fluid within a system, these are typically
employed as ON/OFF switches to control electrical elements.
Adjustments of an Air Compressor Pressure Switch
The features for adjusting the air compressor pressure switch
are always accessible inside the cover. Therefore, it's okay to
follow the instructions below when one doesn't have the
The principal adjustment instruction is to turn the primary
spring in a clockwise or counterclockwise direction to increase
or decrease the cut-in or cut-out settings. The air compressor's
differential can be raised or lowered.
How to Test an Air Pressure Switch
The following procedures are used while testing an air pressure
switch. The procedures are as follows.
Disconnecting the power is the first step in testing the
pressure switch. First, the breaker must be unplugged to
The switch's cover can be removed using a screwdriver. For the
task, try removing the central screw.
Cut any blue or brown wires that connect the switch to the
terminal block. However, it is best if the black and white wires
used for power are not cut.
The next step is to apply pressure to the switch using sources
that provide pressure.
Placing the ohmmeter leads to the exposed wires is the next
step. During the application of air, shut the switch. After the
switch closes, the ohmmeter should read zero, indicating that
the air pressure is in good condition.
The setpoint screw is then used to adjust the pressure switch.
Construction of an Air Pressure Switch
Different parts are used to build a pressure switch, including a
diaphragm, adjustment spring, auto/off lever, electrical
contacts, and terminals.
An air pressure switch measures pressure using a diaphragm that
functions as a detection element. Usually, a plastic,
pressure-responsive polymer is used to create this component.
The set of cut-out points can be altered via an adjustment
spring. In addition, some switches' set and cut-out points are
controlled by independent springs.
The switch can be manually activated or deactivated using an
AUTO/OFF lever. When installing or doing maintenance, using this
lever to turn off the switch is quite beneficial. The knob is
occasionally used in place of a lever, but its operation is the
Once they come into contact with an external power source,
electrical contacts allow current to flow through them. The
switch's terminals link the contacts to an external power
source. For example, a pressure switch operates an electrical
circuit when a fixed liquid pressure is reached. When the
pressure changes from a certain preset level, this switch will
create electrical contact, depending on whether the pressure
rises or falls.
The specifications of the pressure switch include the following.
It spans from -1 to 250 Bar.
At 250/125 Vacs, the contact rating is 5a, 10a, and 15a.
Process connections come in sizes of ¼”,½”, ¾”, ⅜.”
BSP or npt Threaded (m/f)
The switch can be a 1spdt, 2spdt, or dpdt type.
Aluminum is die-cast in the casing.
Protection can be flameproof, weatherproof, or ip66.
180° C is the highest operating temperature.
Field, online, wall, and back panel mounting are all options.
Mechanical and electronic pressure switches are the two
varieties offered on the market.
Electronic Pressure Switches
Electronic pressure switches have a pressure transducer similar
to a strain gauge. These switches' analog capabilities enable
them to deliver a continuous and varied signal for more precise
monitoring rather than being limited to an open or closed
position. These are, therefore, transmitters or measuring
devices in addition to switches. These electronic switches also
have features like switching functionality, on-site time delay,
hysteresis, setpoint, etc. A few benefits are greater accuracy,
less contact wear, superior long-term stability, ease of use,
and the capacity for millions of switching cycles.
Mechanical Pressure Switches
These short and durable switches make them popular choices for
simpler jobs. A spring and a piston control the pressure at
which mechanical pressure switches are activated. The spring,
which opposes the inlet pressure, has a tension that may be
changed using a set screw or knob. The pressure where an
electric contact occurs is directly related to the spring
tension. When the pressure drops, the switch returns to its
initial setting. The mechanical pressure switch is better
equipped to handle high voltages and amperages than an
electronic pressure switch. Through a change in contact, one can
utilize them to raise or decrease pressure.
These switches are more frequently utilized than electronic
pressure switches due to their reduced cost and simplicity.
These switches can be ordered with a mechanical
pressure-detecting component that deforms in response to the
fluid pressure. These switches fall into one of two categories,
electronic or electromechanical, depending on how pressure is
detected. Below is a discussion of the many mechanical pressure
Piston Pressure Switches
This switch is the most well-liked and frequently employed in
various applications. When the liquid's pressure changes, the
piston is moved axially, which activates the switch. This switch
can directly or indirectly detect liquid pressure. Therefore,
O-ring seals are primarily used in direct detecting to prevent
liquid from entering the components. In contrast, a flexible
diaphragm is primarily used in indirectly detecting to separate
the piston from the liquid.
Diaphragm Pressure Switches
These switches are of a high caliber and were created primarily
for applications that required safety. The fundamental advantage
of these switches is that switching doesn't require a voltage
supply. Instead, the diaphragm activating the switch is
connected directly to the drenched portion of the switch by a
metal membrane. This switch monitors pressure and manages
processes in various industries, including chemical,
petrochemical, gas, and oil.
Bourdon Tube Pressure Switches
One end of the switch is connected to this elastomeric or
flexible metallic tube, while the other is left unattached. When
the liquid pressure inside the tube increases, it tends to level
out, and this movement is mostly employed to turn on the switch.
As a result, these switches can be used in various industries,
including chemical, conventional power plants, and petrochemical
plants, wherever a middle-to-high operating force is required.
Differential Pressure Switches
This switch is highly helpful in analyzing the forces between
two places inside a system. The two system points are connected
to the equipment's upside and downside through two process
ports. A switch can be activated if the pressure differential
between the two sides exceeds a predetermined threshold. These
switches can be used to monitor the levels of tanks, filters,
and screens for pressure drop.
Chapter 4: Differences Between Flow Switches and Pressure
The following aspects set a flow switch apart from a pressure
While a pressure switch is used to turn ON/OFF an electrical
circuit by pressure, a flow switch is used to monitor the rate
of water flow and the pressure of air and liquids through a
system, duct, or loop.
While a pressure switch is also known as a pressure sensor, a
flow switch is also known as a flow indicator or flow sensor.
The identification of water flow activates flow switches.
Typically, one to two gallons of water pass through before the
pressure switch switches ON when the pressure is lower than 500
PSI. Once the pressure between 500 and 700 PSI is reached,
pressure switches start to work. This switch can activate the
hot water burner once the pressure reaches this level.
Engine-driven hot water pressure washer machines can use flow
switches. Pressure switches are appropriate for situations
requiring lower hot water pressure.
Chapter 5: Diagram of an Air Pressure Switch Circuit
Below is a diagram of a pressure switch circuit with a
force-sensing resistor. Typically, it is extremely easy to
construct lighting circuits or switches activated by sensors.
Here, we'll outline the design process for an AC pressure
switch. This circuit is employed in numerous applications,
including pressure monitoring, theft alarms, and automatic room
Pressure Switch Circuit Using FSR
A sensor, such as a force sensing resistor, or FSR, is required
to design this pressure switch circuit. In general, an FSR is a
resistor that changes resistance levels in response to force.
However, the force-sensing resistor's resistance will drop to
100 kiloohms as soon as force is applied. Furthermore, if a
strong force is applied to the sensor plate, this resistance
will decrease to 100 ohms.
This circuit begins to operate when FSR detects a force applied
to its plate. R1 and FSR are linked in series to provide a
The comparator's non-inverting terminal receives the output
voltage from this divider. Alternately, R3 and a variable
resistor can create another voltage divider pair (RV1).
Therefore, the comparator's inverting terminal can receive this
divider's output voltage. Here, the pressure or triggering
voltage in the circuit is controlled by a variable resistor.
When no force is applied, the output voltage of the FSR and R1
pair will be lower than the output voltage of the RV1 and R3
pair. Like the resistor, when force is applied, the resistance
decreases, increasing the voltage divider pair output. The
voltage at the comparator's non-inverting terminal will now be
higher than at the inverting terminal. As a result, the
comparator's output will be high, turning on the attached
transistor like a switch.
After that, any AC appliance with a 12A current rating is
activated using a 12V relay. A 2N2222 triggers the relay because
the LM193IC output is low. To protect the rest of the circuit
from the reverse current that comes on when the relay is
switched off, the "D1" diode serves as a safety component.
Chapter 6: Calibration of Pressure Switches
Pressure switches must be calibrated like many other instruments
to ensure their accuracy and dependability. However, switch
calibration requires more effort than transmitter calibration.
Therefore, the wrong calibration can lead to several
inaccuracies in the outcome. So, in this section, we'll talk
about how to calibrate pressure switches correctly. The
following procedures are used to perform the calibration
procedure for this switch.
Connect the switch to the pressure source in the first step. For
instance, a hand pressure regulator and test gauge connect a
pressure source, such as an air supply.
The switch contacts are continuously checked in the second stage
to see if they are showing as normally closed (NC) or normally
opened (NO) using a digital multimeter or an ohmmeter.
In the third step, connect the ohmmeter between two switches,
such as the NO and NC. Again, the ohmmeter readings must be
"open circuit." The hand pressure regulator must now be adjusted
to increase the pressure toward the switch's setpoint until the
switch contacts the switch.
The ohmmeter should now indicate "short circuit." Don't decrease
the pressure reading because this pressure is the switch's set
point for increasing pressure.
Increase the air pressure toward the switch to its highest
setting in the fourth stage. Once the switch is closed,
carefully lower the pressure until it is typically open. Again,
take note of the pressure reading because this is the switch's
setting for lowering pressure.
Check the pressure differential between the rising and
decreasing pressure settings in the final step using the values
acquired. This pressure differential is referred to as the
switch's dead band, and the dead band determined must be equal
to or lower than the manufacturer's dead band. Typically, the
manufacturer will mention the largest dead band value. The
switch is unserviceable if the maximum dead band value exceeds
the manufacturer's recommendation.
Chapter 7: Components of Air Pressure Switches
Auto/Off (Lever Or Knob)
Start by talking about the pressure switch's lever or knob.
Depending on the type and brand of the pressure switch, there
may be a difference in some circumstances.
Some switches may have a lever on the right or left side. At the
same time, the top of some pressure switch models will have a
red knob. Both perform the same task of separating the contacts.
Incoming and outgoing power cords should be connected to
terminals in these areas. The terminal's position depends on the
type of pressure switch used.
Contacts are parts that have been made from a conductive
material. 90% silver and 10% nickel are both present in the
Closing the electrical circuit is the contact's main purpose. It
permits power to move in the direction of the motor. However,
the circuit is incomplete when the contacts are open, which
causes the motor to shut off.
The diaphragm comes next on the list of parts. The flexible
material used to build the diaphragm is flexible. The
diaphragm's job is to regulate the contacts.
As air pressure rises, the flexible structure aids in pushing
against the barrier. Finally, achieving the necessary "cut-out
pressure," the diaphragm pushes the contacts apart and turns the
Pressure Relief Valve
This kind of valve releases pressure from the head and line. It
serves as a rescue back door, to put it simply. If, for any
reason, the pressure switch cannot stop the motor from receiving
electricity. The pressure inside the tank rises to a dangerous
level and can explode. Due to this, the PRV features an orifice
that opens up when the pressure rises to a specific level. This
feature is dependent on the air compressor's structure and
workings. The PRV opening is where the surplus pressure in the
tank vents. The compressor can then push it into the tank once
this procedure moves at a tremendous rate, thereby reducing the
pressure and returning it to normal.
The adjustment spring's primary function is to modify the
cut-in/cut-out pressure. There are, however, some pressure
switch kinds that use a supplementary spring. Smaller than the
"primary spring" is the "secondary spring." The secondary
spring's job is to control the cut-out pressure solely, not the
cut-in pressure settings.
Measurement Options and Sensors
One often has a choice between the following sensor types (which
detect pressure in various ways), depending on the system’s
Absolute air pressure sensors measure pressure relative to an
ideal vacuum (this is the least likely choice, except perhaps
for experimental work).
One can measure pressure concerning atmospheric pressure using a
gauge air pressure sensor (in tire pressure measurement, for
example, a zero reading means the internal air pressure is equal
to that of the atmosphere).
The difference in pressure between two places is measured using
a differential air pressure sensor (such as before and after a
filter in an air conditioning system).
The pressurized air and a pointer on the gauge are mechanically
connected in the simplest air pressure gauges. Bourdon tubes and
pistons are often used mechanisms for this. The farther the
pointer moves, the harder the pressure is applied.
However, air pressure sensors, which translate the effect of
pressure into a proportionate electrical output, should be
considered for higher accuracy and control. The term "pressure
transducer" is frequently used to describe this pressure sensor.
Various technologies and operating theories have been applied to
measure pressure accurately, each with advantages and drawbacks
of their own. Below are summaries of the three most popular
methodologies utilized in the field of air pressure sensors.
Resistive Air Pressure Transducer or Strain Gauge
As pressure rises, a diaphragm in contact with the measured air
undergoes deformation. Similar deformation is seen in strain
gauges fastened to the diaphragm's non-contacting surface. The
strain gauge material's resistance changes due to the
piezoresistive action, which is translated into an electrical
Capacitive Air Pressure Switch
This method uses two capacitive plates barely spaced apart from
one another. One is fixed, while the other is a flexible
diaphragm when it touches the air. The diaphragm is deformed as
air pressure rises, which reduces capacitance and causes the gap
to close. The change in capacitance creates an electrical
Inductive Air Pressure Switch
Here, the inductance principle is used to translate the
deformation of a diaphragm into linear movement of a
ferromagnetic core. The induced current, produced by an
AC-powered coil on a different secondary pick-up coil, varies as
a result of the movement of the core. An electrical signal is
then created from this alteration.
Options and Specifications
Applications differ slightly from one another. Therefore, one
must evaluate how well the air pressure switch in the shortlist
satisfies the requirements to make the best, if not ideal,
decision. Here are some standards to bear in mind.
Pressure Spectrum. The pressure spectrum should cover the
maximum pressure permitted by the equipment, at the very least.
Failure of an air pressure switch is frequently brought on by
too much pressure.
Temperature Affects Precision. At ambient temperature, most air
pressure switches are fairly accurate. Still, at higher
temperatures, they are less so. Use digital electronics and a
sensor with a high degree of precision if accuracy is the top
concern. Some sensors provide calibrated and
Location Affects Precision. Sensors may be affected by
vibration, shocks, and extreme temperatures near the equipment
they monitor. Look for a strong design if remote installation is
not an option. Ensure the sensors' housing provides adequate
protection if exposed to hot or humid weather.
Compatibility. Will the sensor's fittings allow one to easily
thread it onto the current setup? Is the signal conditioning
equipment compatible with its analog output?
Response Period. Some pressure transmitters have simple response
time adjustments, which can help prevent erroneous triggering.
Price. One must only spend what they have to, but be aware that
with inexpensive sensors, one will have to give up features like
precision and durability.
Lifetime Expense. Factors including affordability, low
maintenance requirements, durability, and robustness should be
considered along with the purchase price.
There is a wide range of options between capacitive and
resistive air pressure switches. The most popular of them is the
resistive, or strain gauge, category. It has benefits for
protecting against overpressure, resolving issues effectively,
and being resilient in the face of shocks, vibrations, and
dynamically changing pressures.
However, one should know the many material options when choosing
a resistive air pressure transducer for a specific use.
Regarding temperature, humidity, and sensor output stability,
In addition to handling overpressure well, capacitive air
pressure switches are superior to strain gauges for use at low
pressures. Hysteresis, linearity, stability, reproducibility,
and static pressure measurement are all areas in which they
However, they cost more to produce and are bigger. In addition,
particulates and humidity in the space between their capacitive
plates can also harm them.
The air pressure switch's specifications mentioned above can
help one comprehend how it functions and is utilized.
Additionally, one would have learned much about adjustable air
compressor pressure switches. The above information might
produce greater results when one operates pressure switches in
Technicians and pressure switch operators are needed in many
manufacturing and industrial sectors. By mastering the
techniques, one can seize the opportunity for a profitable
profession. Additionally, one must know how pressure switches
are used in the aforementioned suitable systems. This knowledge
would give one a thorough understanding of the applications of
A pressure gauge is a method of measuring fluid, gas, water,
or steam intensity in a pressure powered machine to ensure
there are no leaks or pressure changes that would affect the
performance of the system. Pressure systems are designed to
operate within a specific pressure range...
A pressure transducer is a mechanical device that converts
applied pressure, a physical quantity, into a measurable and
industry-standard electrical signal which is linearly and
proportionally related to the applied pressure...