Last Updated on May 31, 2022 by Kevin Chen
When pressure limits are exceeded, pressure switches are used to control the activation and deactivation of pumps in fluid systems. They’re also needed to keep mechanical or pneumatic pressure constant in process control systems.
When choosing a solution for a certain application, it’s helpful to understand how pressure switches function, the many types of pressure switches, and the common applications.
What is a Pressure Switch?
A pressure switch is an electrical device that measures pressure in a variety of applications & conditions across several industries.
The user sets the activation limit of a pressure switch depending on the application. The pressure switch will change state whenever the activation limit is reached, resulting in a circuit reaction. On the other hand, a pressure transducer provides a precise real-time reading of pressure.
Working Principle of a Pressure Switch
A conventional pressure switch has a piston exposed to fluid pressure on one side. In most cases, the opposing side is under atmospheric pressure. A force opposes the force exerted by a preloaded spring’s fluid pressure. The spring constant & the surface area in contact with the fluid are carefully engineered to move the piston only when a specified pressure is reached. The setpoint screw pre-compresses the spring. Despite the fact that pressure switches use several technologies to measure pressure, they are typically electromechanical or electrical. The setpoint screw is turned to raise or lower the activation pressure.
The cut-in & cut-out pressures are the most common operating points for pressure switches. When the fluid pressure in a pump or compressor system falls below a predetermined level, the switch is actuated. This switches on the pump or compressor’s motor, bringing the system back to normal. The switch does not immediately deactivate when the pressure exceeds the predetermined point; the switch does not immediately deactivate. Sudden tripping is prevented by a type of hysteresis known as a differential. This permits pressure to rise until it reaches the upper limit of the pressure range. The switch deactivates when the higher set point or cut-out is reached.
Parts of a Pressure Switch
The essential components of a pressure switch are discussed in this chapter. It’s worth noting that each type of unique design may have its own set of components. Only mechanical pressure switches are compatible with the parts listed below.
Process (Inlet) Port
The pressure switch assembly is connected to the processing unit via the inlet port. Nozzles attached to a pipe or tank have pressure switches installed. Threaded fittings are a common way to connect. Welded or bolted connections are only utilized in the most extreme circumstances. It’s critical that the fitting’s type and pressure rating match the fluid pressure.
The fluid’s force is countered by the spring. It is preloaded with the fluid’s operational pressure. The switch is only activated when the force from the fluid pressure surpasses the force applied by the spring.
Pressure Sensing Element
Mechanical pressure switches are categorized based on the pressure sensing element. The fluid pressure mechanically actuates the major portion of the switch. The fluid-side region of the piston or diaphragm is designed to transfer enough force from the expected fluid pressure. The greater the area, the greater the actuating power and spring force required. It should be noted that only a modest amount of force is required to activate the switch. The spring absorbs a large portion of the pressure.
Setpoint Adjustment Screw
These setpoint adjustment screws are built inside the spring. It is also used to increase or reduce the activation pressure.
This is used to expand or contract the switch’s operational pressure range. The most typical design observed in pumping systems is a set of springs and adjustment screws smaller than the set point adjustment. Tightening or loosening this screw changes only one end of the pressure range (higher or lower end), while the other end stays unchanged.
Together with the other sealing elements, the diaphragm protects the switch’s insides from the process fluid. It is a flexible material typically composed of elastomers, polymers, or metal alloys. The choice of diaphragm material is determined based on the fluid and its temperature. Common diaphragm & sealing materials include:
Nitrile or NBR (Buna-N)
These materials are very resistant to oils and petroleum-based fluids, although they deteriorate in the presence of ketones and ozone. Nitrile diaphragms & seals have a good balance of physical qualities & cost, making them appropriate for most neutral fluids. Its working temperatures can vary from -30°C to 100°C.
Ethylene Propylene Diene Monomer or EPDM
This is yet another elastomer commonly utilized in high-temperature steam and water operation. Its maximum operating temperature is 250°C. It is resistant to ketones, weak acids, ozone, alkalis, and other oxidizing agents. They are not utilized in petroleum service because EPDM absorbs oils and fuels, causing them to bloat.
Fluorocarbon or FKM (Viton)
Viton is a proprietary polymer having NBR-like characteristics. This substance is not affected by petroleum-based fluids or solvents. They are also unsuitable for fluids containing ketones. Viton has ideal working temperatures that can reach 200°C.
Because of its polymeric chain structure, PTFE is less commonly employed as a diaphragm membrane than the prior materials. It is less elastic than elastomers and is more prone to creep. They are only considered for use in high temperatures of up to 500°C and corrosive or abrasive environments. Teflon (PTFE) is combined with a Kapton layer in the popular PTFE diaphragm (polyimide).
The switch enclosure shields the switch and other internal components from the elements.
The protection grade of the switch casing is an important characteristic. NEMA, ATEX, and IP ratings are common enclosure specifications.
The NEMA and IP ratings reflect the level of protection against the intrusion of solid and liquid foreign objects. The ATEX classification is for environments with a risk of fire or explosion.
The contacts are one of the switch’s conducting components. The electrical circuit is de-energized or energized when the contacts are separated or linked. Switch contacts are made of both corrosion-resistant and electrically conductive materials, such as silver, gold, copper, or brass. Contacts might be NC, NO, or CO in terms of their connections. NO is used for de-energized circuits that cut in at the setpoint. NC does the inverse by being first energetic. CO switches control two links or circuits, one open and one closed, and are typically used to control interlocking or more complex circuits. NO or NC is sufficient for simple control activation.
This is the location of the control or instrumentation circuit. The configuration of the terminals in relation to the contacts is usually indicated on the nameplate of a pressure switch. The nameplate contains schematics or diagrams that can be used to determine the proper terminal connection in the circuit. The terminals, like the contacts, must be highly conductive and corrosion-resistant.
Pressure switch Types
Mechanical Pressure Switch
Mechanical pressure switches are used when a micro-switch is actuated by using a spring and a diaphragm or piston. The spring acts as an opposing force to the inlet pressure, and its tension is adjustable via a set screw or knob. The pressure at which the switch creates an electric contact is precisely proportional to the spring tension. The switch returns to its original state when the pressure drops.
Hysteresis refers to the disparity between the switch point and the reset point. This is sometimes represented as a percentage of the switch point value, such as 20%. The manufacturer determines the hysteresis, and it is not changeable by the user for most mechanical switches.
These pressure switches typically have three types of contacts: normally open (NO), normally closed (NC), and changeover (SPDT). Changeover contacts are used for both NO and NC activities.
A mechanical pressure switch is more suited to handle high voltages & amperages than an electronic pressure switch. They can be used to adjust the contact to raise or decrease pressure. The mechanical pressure switch is categorized based on the type of pressure sensing component.
Piston Pressure Switch
This is the most common and commonly used pressure switch. The piston moves axially when the fluid pressure changes, activating the switch. It can detect fluid pressure directly or indirectly. Seals, such as O-rings, are used in direct sensing to prevent fluid from accessing the electrical components. In indirect sensing, the piston is separated from the fluid by an elastic diaphragm.
Diaphragm Pressure Switch
This type is made up of a metal membrane connected or welded directly onto the wetted area of the pressure switch. Instead of a piston, the diaphragm immediately activates the switch.
Bourdon Tube Pressure Switch
A bourdon tube is an elastomeric or flexible metallic tube that is fixed at one end yet free to move. When the pressure inside the tube is increased, it tends to straighten. This motion is then employed to turn on the switch.
Differential Pressure Switch
This is a pressure switch that compares the pressures at two places in a system. These locations are linked to two different process ports. These can be either upstream or downstream of equipment or on the top or bottom of a vessel. The switch is engaged when the pressure difference between the two sides surpasses a specified level. These can be used in interlocking controls to monitor pressure drop across screens, filters, and tank levels.
Electronic (Solid-state) Pressure Switch
A pressure transducer, often a strain gauge, is combined with proprietary electronics that amplify & transform signals into a viewable display in an electronic pressure switch. The majority of electronic pressure switches are analog capable. This means they are not restricted to an open or closed position but can instead send a continuous, changing signal for more accurate monitoring.
Therefore, electronic pressure switches are transmitters or measurement equipment rather than switches. Electronic pressure switches have on-site programmability for setpoint, hysteresis, time delay, switching function, and other features.
What Is a Pressure Switch Used for?
The pressure switch is used in various industries for a variety of applications. The air pressure switch provides electrical feedback by sensing the temperature rise and fall of the system.
The air pressure switch is widely utilized in industrial control systems. The following are some of the systems where air pressure switches can be found.
Compressed Air Systems
The operation of the air compressor system has already been described above. Aside from the information provided above, you should comprehend the significance of the pressure switch. The compressor function does not reach the desired height if the pressure switch fails.
HVAC equipment, which can be found in residential and commercial buildings, provides both heating and cooling functions. Pressure switches are used in HVAC equipment for safety reasons—Air pressure switches in HVAC equipment aid in detecting min and max set points. The feature can be found in air conditioning systems.
This function assists the system in starting or stopping depending on the setpoint level. Yes, you will have a trouble-free HVAC system operation since the pressure switch allows the system to turn on and off automatically. If the air pressure switch fails to function correctly, the heating and cooling system’s performance deteriorates.
Air pressure switches are frequently utilized in the manufacturing industry. The air pressure switch assists companies and manufacturing sectors in meeting their objectives without gaps. The pressure switch improves production efficiency in any manufacturing industry. Yes, the switches enable a continual flow of gas and fluid for the continued operation of industrial equipment.
The primary function of air pressure is to maintain the water level in the pumps. Water pumps are engaged and deactivated by the pressure switch based on the specified points.
The information provided above about the air pressure switch will help you understand how it works and is utilized. You would also have learned a lot about adjustable air compressor pressure switches. If you happen to work with pressure switches in your field, the information provided above may help you achieve better results.
Pressure switch operators are needed in a variety of industries and manufacturing sectors. Knowing the approaches will allow you to capitalize on the opportunity for a lucrative profession. You must also comprehend the functions of pressure switches in the systems mentioned above. This would provide you with a thorough understanding of the applications of pressure switches to your fundamental understanding.
For more details on Pressure switches, contact us at ICRFQ. We manufacture the best electrical components in China.
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