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A pressure switch is a device—either mechanical or electronic—that is activated by the pressure of fluids, air, or gases reaching a predetermined level. These switches are designed using components such as bourdon tubes, pistons, diaphragms, or membranes that react or shift in response to the system's pressure changes.
Pressure switch components are connected to one or more contacts within the device. When adequate pressure is applied, a contact either closes or opens, based on the switch's setup. Although various methods exist for pressure detection, pressure switches can be primarily classified into electromechanical or electronic categories.
Pressure switches are vital across numerous industries, including those utilizing compressed gas systems, HVAC systems, as well as instrumentation and pumping systems.
In a typical pressure switch, a piston is present with one side exposed to the fluid's pressure and the other to atmospheric pressure. The fluid pressure's force works against a preloaded spring. The portion in contact with the fluid, along with the spring constant, is engineered to ensure the piston moves only when a designated pressure level is attained. The spring’s tension can be changed via an adjustable setpoint screw to modify the activation pressure.
Pressure switches typically operate between two key points: the cut-in and cut-out pressures. In systems like pumps and compressors, the switch engages when the fluid pressure drops below a predetermined level, triggering the motor to restore system pressure. The switch doesn’t deactivate immediately as pressure exceeds the set limit; there is a differential, or hysteresis, that prevents abrupt shut-off. This delay allows pressure to rise until the upper threshold, or cut-out level, is achieved, at which the switch turns off.
This chapter discusses the main parts of a pressure switch—a critical component in industrial automation, fluid control, and safety monitoring systems. Understanding the anatomy of a mechanical pressure switch is essential for optimizing process reliability and selecting the right product for your application. Note that each type or proprietary design may include additional components for specialized needs. The parts mentioned below apply specifically to mechanical pressure switches, which are widely used in various industries for their durability and straightforward operation.
The inlet port connects the pressure switch assembly to the process unit, allowing pressurized fluid (liquid or gas) to enter the device. Pressure switches are typically installed on nozzles connected to a tank or pipe, with threaded fittings such as NPT (National Pipe Thread) being the most common connection in HVAC, water treatment, hydraulic, pneumatic, and industrial process systems. In rare cases, bolted or welded connections are used for high-pressure or custom installations. Proper selection of fitting type and pressure rating is critical to prevent leaks and ensure the connection is compatible with both the fluid pressure and the material chemistry (e.g., stainless steel for corrosive processes). This helps maintain system integrity and supports accurate pressure measurements.
Mechanical pressure switches are classified according to their pressure-sensing element. This element, often designed as a piston, bellows, or diaphragm, is the main part of the switch that mechanically actuates in response to the process fluid pressure. The effective area of the piston or diaphragm on the fluid side is carefully engineered to translate the expected range of pressure into a measurable force. The larger the area, the greater the actuating force and spring force required. It’s important to note that only a minimal actuation force is needed since the switch spring offsets most of the applied pressure. This makes these switches sensitive and responsive to setpoint changes, allowing for precise pressure control and regulation in applications such as compressors, pumps, and safety alarm systems.
The spring counters the force from the fluid and is preloaded to match the desired operating pressure setpoint. The mechanical pressure switch activates (changes contact state) only when the force generated by the process pressure exceeds the spring’s resistance. Spring selection and calibration are fundamental for setting both the pressure setpoint and the pressure differential (also known as switch deadband or hysteresis). Quality springs contribute to repeatable actuation points and long-term accuracy, directly impacting the reliability of pressure monitoring and process automation systems.
Integrated with the spring is the setpoint adjustment screw, a feature that allows users to easily increase or decrease the switch activation pressure. This adjustability is essential for field calibration, ensuring the pressure switch meets specific operational requirements during installation, commissioning, or routine maintenance. Proper use of the setpoint adjustment screw supports optimal system performance and safety compliance.
This adjustment sets the pressure differential (or hysteresis), allowing you to widen or narrow the operating pressure range of the switch. In many pumping or compressor systems, a dual-spring arrangement and corresponding adjustment screws are provided. The smaller screw, typically located near the main setpoint screw, fine-tunes the switch’s pressure range on either the high or low end. Adjusting the differential prevents rapid cycling and nuisance tripping, thereby increasing equipment life and operational stability. Understanding and setting the correct differential is vital for applications such as level control, leak detection, and overpressure protection, where process stability is paramount.
The diaphragm, along with O-rings and other sealing components, forms the primary barrier protecting the internal parts of the switch from direct contact with the process fluid. This not only ensures switch longevity and prevents corrosion but also maintains the accuracy of pressure sensing functions. Diaphragm materials are selected based on chemical compatibility, fluid type, and temperature requirements. Popular choices include elastomers, fluoropolymers, and specialized alloys, each offering unique performance characteristics across various industrial environments:
These materials are highly resistant to oils and petroleum-based fluids but can degrade when exposed to ozone and ketones. Nitrile diaphragms and seals offer a good balance of cost and physical properties, making them suitable for most neutral fluids, general-purpose industrial, and HVAC applications. Their operating temperature range is -30°C to 100°C, supporting versatility across pressure switch types used in oil, fuel, and air systems.
EPDM (ethylene propylene diene monomer) is a popular elastomer for applications requiring high-temperature water and steam service. It withstands operating temperatures up to 482°F (250°C) and is highly resistant to ozone, ketones, mild acids, alkalis, and other oxidizing chemicals. However, EPDM is unsuitable for petroleum-based applications, as it may absorb oils and fuels, resulting in swelling or premature failure. EPDM is commonly found in pressure switches used for municipal water systems, boilers, and chemical processing.
Viton, a proprietary form of FKM, offers exceptional resistance to petroleum-based fluids, solvents, and aggressive chemicals, making it an ideal material for harsh operating environments such as refineries, chemical plants, and high-temperature industrial processes. With an operational range that can reach up to 200°C, Viton outperforms many other elastomers in terms of heat resistance and chemical stability, but should generally not be used with fluids containing ketones.
PTFE (polytetrafluoroethylene, best known as Teflon) is less commonly used as a diaphragm membrane than elastomers due to lower elasticity, which makes it prone to creep and reduced flexibility. PTFE, however, is the material of choice for extreme high-temperature environments (up to 500°C), aggressive chemicals, corrosive fluids, and abrasive slurries. Combination diaphragms featuring Teflon and Kapton (polyimide) further extend temperature and chemical resistance. PTFE-sealed pressure switches are vital in pharmaceutical, food & beverage, and chemical processing industries where process purity and resistance to attack are crucial.
The switch housing ensures mechanical and environmental protection for the sensitive internal components. A crucial specification of the switch housing is its protection rating. Whether for indoor industrial automation, outdoor water systems, or hazardous locations, choosing the correct enclosure rating—such as IP (Ingress Protection), NEMA (National Electrical Manufacturers Association), or ATEX (for potentially explosive atmospheres)—is essential. IP and NEMA ratings provide details about the level of protection against dust, water, and other environmental hazards, while ATEX compliance is mandated for areas where sparks or heat could ignite flammable gases. These factors must be considered to meet local safety codes and maintain uninterrupted system operation in demanding environments.
The contacts are the conductive parts of the switch responsible for either energizing or de-energizing the electrical circuit by separating or linking. They are made from materials with high corrosion resistance and electrical conductivity, such as copper, silver, gold, or brass. Contacts can be normally open (NO), normally closed (NC), or changeover (CO). NO contacts are initially de-energized and close at the setpoint, while NC contacts are initially energized and open at the setpoint. CO switches have two connections or circuits—one normally open and one normally closed—and are used for applications such as control interlocking or more complex circuits. For simple control activation or alarm functions, NO or NC contacts are typically sufficient.
The terminal is where the control or instrumentation circuit connects to the pressure switch. Most pressure switches have markings on their nameplate that indicate the terminal configuration relative to the contacts. The nameplate often includes schematics or diagrams to guide correct terminal connections in the circuit. As with contacts, selecting terminals with corrosion resistance and high conductivity is important to maintain signal integrity and ensure dependable operation over time. Proper terminal wiring is vital for safety, reliability, and efficient troubleshooting, especially in automated process control or building management systems.
When selecting a pressure switch for industrial, commercial, or residential applications, it’s important to consider additional factors such as:
By considering these technical aspects along with the detailed part descriptions above, users and engineers can confidently select the best pressure switch for process automation, equipment protection, or fluid control applications. For help with product selection, custom designs, or sourcing top-rated models, contact leading pressure switch manufacturers and suppliers specializing in industrial automation, instrumentation, and control solutions.
There are two main types of pressure switches: mechanical pressure switches and electronic pressure switches. Mechanical pressure switches are further categorized based on the design and construction of their pressure-sensing mechanisms—such as pistons, diaphragms, or Bourdon tubes. Electronic pressure switches, also known as solid-state or digital pressure switches, utilize advanced sensor technologies and integrated circuitry for indirect actuation based on varying electrical properties like resistance or capacitance. Understanding the distinct features and operational benefits of each type is essential when selecting the right industrial pressure switch for a specific application.
The previous chapters primarily describe mechanical pressure switches, which remain a staple in industrial automation and process control due to their reliability, robustness, and cost-efficiency. In these devices, a mechanical element physically interacts with the pressure medium, triggering an electrical contact at a defined set point. The durability and straightforward operation of electromechanical switches make them ideal for use in machinery, automotive systems, and fluid handling equipment where rapid pressure response and basic ON/OFF control are required. Mechanical switches are typically categorized by the type of pressure-sensing component they employ.
The piston pressure switch is among the most widely utilized types in both industrial and commercial pressure control systems. As fluid pressure increases or decreases, the piston moves axially, directly or indirectly operating the electrical contacts. For direct sensing, robust O-ring seals are used to isolate the electrical compartment from process fluids, ensuring safe operation. Indirect sensing may use an elastic diaphragm to decouple the piston from the process medium—important in handling corrosive or hazardous fluids. Their adaptability and ruggedness make them suitable for hydraulic pressures, oil & gas systems, and pipeline monitoring.
The diaphragm pressure switch features a metal or elastomeric membrane that responds to changes in process pressure. The membrane is typically welded or otherwise joined directly to the wetted area for high reliability. The flex of the diaphragm actuates the switch, providing excellent sensitivity for lower pressure ranges, and making these switches valuable in sanitary, food processing, and automotive transmission systems where contamination resistance is crucial.
A Bourdon tube pressure switch contains a specially-coiled metallic (or elastomeric) tube sealed at one end. An increase in pressure inside the tube attempts to straighten it, and this mechanical motion is transferred to switch actuation. Bourdon tube switches are renowned for their repeatability and are widely deployed in steam systems, compressed air systems, and other high-pressure monitoring applications.
A differential pressure switch is engineered to measure the pressure difference between two points within a process, such as the inlet and outlet of filters, pumps, or turbines. Two process ports connect to different zones, and the switch actuates if the pressure delta across them surpasses a specified set point. This type is vital for interlock control, signaling filter blockage, and monitoring fluid flow rates or tank levels. Differential pressure switches are commonly used in HVAC systems, clean room environments, water treatment plants, and fire protection systems to ensure operational safety and efficiency.
A snap disc pressure switch utilizes the rapid movement of two metal discs—snapping between convex and concave positions in reaction to specific pressures. The presence of a diaphragm between pressure and disc chambers ensures accurate actuation and protects sensitive internal mechanisms. These switches are engineered for precise control of switching points under varying pressure loads, supporting applications such as aerospace (e.g., reentry parachute deployment), temperature monitoring, and high-current electrical circuits where reliability and repeatability are paramount.
The consistent performance and high accuracy of snap disc switches also make them suitable in industrial boilers, appliance safety features, HVAC controls, and various critical process automation tasks.
Notably, snap disc pressure switches deliver longevity and reliability, often with long service intervals and low maintenance requirements. Their compact design and quick response characteristics have proven essential in both military and commercial aerospace missions, as well as everyday process environments.
An electronic pressure switch, often referred to as a solid-state or digital pressure switch, incorporates a pressure transducer—typically a strain gauge or piezoelectric sensor—coupled with advanced microelectronics to amplify and process the sensor output. These switches provide precise digital readouts, and many models offer programmable features including user-selectable set points, time delays, hysteresis adjustments, and multiple output signals (analog or digital). This functionality allows for real-time monitoring and control within automated process systems, supporting both ON/OFF relay switching and continuous variable output for data logging or SCADA integration.
Electronic pressure switches excel in scenarios demanding superior accuracy, rapid response, long-term stability, and data communication capabilities. They are favored in industries such as pharmaceuticals, water treatment, industrial automation, and food processing, where tight pressure control, diagnostic features, and ease of recalibration are critical to maintaining quality and compliance.
High pressure switches are purpose-built to withstand and operate reliably at pressures ranging from 1 psig up to—and exceeding�10,000 psig, with common ratings at 4,500 psig or 7,500 psig. Actuation mechanisms can include metal diaphragms, precision-engineered pistons, or rugged piezoelectric sensors. Among these, diaphragm-activated high pressure switches are prevalent for their rapid response and containment capabilities.
These devices are indispensable in applications where failure or loss of pressure control could result in hazardous conditions, such as in chemical processing, hydraulic press operations, wellhead pressure monitoring, and in explosion-proof or waterproof system designs. Materials used may include stainless steel, Monel, Hastelloy, or aluminum, chosen for their corrosion resistance, high tensile strength, and long-term durability—factors essential for maintaining performance in harsh and demanding environments.
Advanced high pressure switches may also feature tamper-proof housing, integrated overpressure protection, and optional remote status indication. Their role in ensuring equipment safety, system longevity, and compliance with relevant industry standards (such as ATEX or IECEx for hazardous locations) underscores their importance in pressure management strategies.
Low pressure switches—also referred to as light pressure switches—are engineered for highly sensitive detection of small pressure fluctuations or reductions. They provide vital protection against system downtime or damage caused by insufficient pressure, acting as failsafes by shutting off pumps, compressors, or entire processes when minimum pressure thresholds are not met.
These switches incorporate a range of actuation methods, including precision diaphragms, lightweight pistons, and delicate piezoelectric assemblies, offering exceptional repeatability and rapid response. Commonly used in pneumatic systems, medical devices, laboratory equipment, and hydraulic circuits where maintenance of consistent pressure is mission critical, low pressure switches are valued for their low actuation points and minimal drift over time.
Subcategories include differential low pressure switches, which measure differential pressure across system components and initiate control based on pre-set ranges, as well as positive and negative pressure switches, which translate respective increases or decreases in pressure into electrical signals. These features make low pressure switches indispensable for leak detection, filter monitoring, and air flow verification in energy management systems and automated environmental controls.
There are numerous specialized types of pressure switches, each tailored to support unique industrial processes, enhance safety, and optimize system performance. Beyond the elementary mechanical and electronic classifications, distinct models can be selected to address niche requirements in different sectors.
Adjustable Pressure Switches: These versatile switches empower users to set activation pressure points to meet dynamic application needs, making them ideal for pump control, irrigation, compressor management, and refrigeration systems. To optimize energy efficiency and minimize wear on connected equipment, adjustable switches are widely adopted in HVAC, food production lines, and process automation.
Air Pressure Switches: Vital for pneumatic automation, these switches monitor and control air pressure in tools, compressors, HVAC equipment, pneumatic conveying systems, and industrial clean rooms. Their rapid response ensures system safety, air quality, and regulatory compliance in manufacturing and packaging environments.
Gas Pressure Switches: Gas pressure monitoring switches are engineered for both residential and industrial setups. They are essential in maintaining gas pressure in pipelines, combustion controls for furnaces and boilers, and emergency shut-off functions in gas-fired appliances and chemical plants. Integral safety features help prevent gas leaks and fire hazards.
Oil Pressure Switches: Specifically designed for fluid systems, oil pressure switches are used to safeguard engines, hydraulic actuators, compressors, and industrial pumps by ensuring oil pressure remains within designated limits. Their role in preventive maintenance helps avoid critical failures, overheating, and expensive downtime in high-value industrial assets.
Hydraulic Pressure Switches: Hydraulic pressure switches serve as safety interlocks and operational controls within hydraulic circuits for construction, manufacturing, and agricultural machinery. By monitoring hydraulic line pressure, they activate alarms, shutoffs, or alternative circuits, providing real-time protection and optimal performance in machinery under heavy load or variable operating conditions.
Vacuum Switches: These measuring devices detect and maintain vacuum levels in closed or open systems, with electromechanical, solid-state, or pneumatic versions available. Their configurations address a spectrum of needs, from simple process alarms to sophisticated leak detection systems in semiconductor manufacturing, packaging, pharmaceuticals, and automotive brake systems. Users can choose from normally open (NO), normally closed (NC), and multipole-multithrow variants for greater application flexibility.
Well Pressure Switch: A well pressure switch manages the activation of submersible well pumps based on water system pressure, preventing over-pumping and protecting against dry-running. By precisely defining cut-on and cut-off points, these switches not only safeguard the well and extend pump life but also stabilize water supply in residential, commercial, and agricultural settings. Selection of the correct set point and maintenance are critical for optimal well pressure switch operation.
When selecting among these pressure switch types, consider factors such as pressure range, media compatibility, switching accuracy, electrical rating, environmental conditions, and certification requirements. Careful assessment ensures operational safety, cost-effectiveness, and regulatory compliance in every pressure switch application.
As with any measuring or monitoring device, selecting a pressure switch involves several criteria that must be considered. Choosing the appropriate pressure switch for a specific application can lead to reduced costs and extended service life of the device.
The chemical properties of the process fluid dictate the choice of materials for the wetted parts, which include the ports, seals, and the pressurized side of the pressure-sensing component. These parts must be able to withstand any chemical or physical damage from the process fluid. Potential degradation mechanisms include corrosion, oxidation, or erosion. Commonly used materials for the rigid parts are steel, brass, stainless steel, PTFE, and polypropylene (PP), while elastic pressure-sensing components and seals typically use NBR, EPDM, and FKM.
The operating temperature affects the choice of materials for pressure switches, as certain materials can degrade at high temperatures. Materials suitable for high-temperature service include FKM and stainless steel 316. It is crucial to ensure that the temperature of the media being measured is within the manufacturer’s specified temperature range for the switch.
The impact of temperature on accuracy should also be taken into account. If a pressure switch is calibrated at room temperature, the setpoint might need to be readjusted when the process operates at a higher temperature. Additionally, fitting connection sizes for pressure switches typically range from 1/8 to 1/2 NPT.
The pressure range defines the limits within which the cut-in and cut-out pressures can be adjusted, commonly referred to as the working range of the pressure switch. It is advisable to set the switch at 40 to 60% of the pressure range to allow for potential adjustments or field changes.
Pressure switches are commonly used in positive pressure systems, but they can also be applied in vacuum environments. For negative pressure systems, it is essential to use pressure switches specifically designed for vacuum and compound pressure applications.
Switches can be characterized by the number of poles and throws. The pole refers to the number of circuits a switch can control, while the throw indicates the number of connections the switch can make. Both poles and throws can be single or double. The classifications for switching functions are as follows:
This is the basic on/off switch, which can be either Normally Open (NO) or Normally Closed (NC).
This is the most versatile switch, capable of functioning as Normally Open (NO), Normally Closed (NC), or Changeover (CO). It can also have three positions, with the center position being off for a CO switch. This configuration is known as single pole, triple throw, though it is rarely used for pressure switches, which typically have only two positions.
This configuration is similar to having two Single Pole Single Throw (SPST) switches connected to a common actuator.
This configuration is equivalent to having two Single Pole Double Throw (SPDT) switches controlled by a common actuator.
This refers to the difference between the cut-in and cut-out pressures of a pressure switch. Pressure switches can have either adjustable or fixed deadbands. Adjustable deadbands are commonly used in water pumping services, allowing for flexibility in setting the pressure range. Fixed deadbands are often found in packaged equipment and alarm systems, where modifications are either not needed or are avoided to prevent accidental changes. Generally, diaphragm and bourdon tube pressure-sensing elements have a narrower deadband compared to piston-based switches.
Proof pressure is the maximum pressure a switch can endure without altering its properties or performance. It is also referred to as over-range capacity or maximum system pressure. Determining the proof pressure takes into account potential pressure spikes or surges within the system.
Accuracy refers to the maximum positive or negative deviation from the setpoint or specified characteristic curve under specific conditions and operations. It is a crucial factor when selecting analog pressure sensors and electronic pressure switches. Higher accuracy often results in increased costs for these devices. Accuracy is typically expressed as a percentage of the full scale (FS) value. For diaphragm and bourdon tube pressure switches, accuracy is usually ±0.5%, while piston pressure switches have an accuracy of ±2%. Electronic pressure switches generally offer better accuracy, ranging from ±0.2% to ±0.5%, depending on the manufacturer.
Repeatability refers to the deviation between measurements or activations at the same pressure. Unlike accuracy, which measures how close a device's performance is to the setpoint, repeatability indicates how consistently a device performs at the same pressure. A pressure switch can exhibit high repeatability by activating at the same pressure repeatedly, even if those activations are not close to the setpoint. Repeatability, like accuracy, is specified as a percentage of the full scale (FS) value.
This refers to the expected period between two activations of a pressure switch. It's important to consider this factor because continuous deformation of the pressure-sensing element can lead to fatigue, reducing its service life. Piston and bourdon tube pressure switches, which operate on deformation principles, are more suited for low-cycling applications. For high-cycling applications, piston and electronic pressure switches are preferable. Piston pressure switches experience less fatigue as their actuation relies primarily on the movement of the piston or plunger. Electronic pressure switches also have lower fatigue since the deformations in a strain gauge are minimal compared to mechanical sensing elements.
The service life of a pressure switch is directly influenced by the speed of cycling and refers to the expected number of times the switch can activate and deactivate before failure. Electronic pressure switches, being solid-state devices with no moving parts, generally offer superior service life, often exceeding one million cycles. Among mechanical pressure switches, piston switches tend to have a longer service life compared to bourdon tube and diaphragm switches.
This specifies the electrical characteristics of the control circuit. The pressure switch must be rated for the same current, voltage, and frequency to ensure proper activation and accuracy. Mismatched ratings can lead to malfunction or reduced performance, particularly in electronic switches. Control circuits that use pressure switches are typically DC, but AC voltages are also used in some cases. Common DC voltages include 8, 12, 24, and 30 volts, while AC voltages at 60Hz commonly include 24, 120, 240, and 480 volts.
The fitting connection on the pressure switch must match the process stub connection or pressure port. Male and female threaded connections are commonly used for mounting pressure switches, with sizes ranging from 1/8 to 1/2 inches. In addition to size and type, the material of the fittings should be selected based on the environment and compatibility with the connection to prevent corrosion, whether from atmospheric conditions or galvanic processes.
This determines the environmental protection the switch housing can provide. Pressure switches are used across various industries, necessitating different enclosure designs to balance durability and cost. Protection ratings are specified through NEMA and IP numbers. Generally, higher NEMA numbers indicate better protection levels, while IP numbers consist of two digits: the first digit represents protection against solids or particulates, and the second digit represents protection against liquids. For general indoor use, NEMA 1 to 2 or IP 10 to 11 offer adequate protection from personnel contact. For outdoor use, NEMA 3S to 4X or IP 54 to 64 protect against dust, rain, and snow. For environments requiring occasional washdown or immersion, NEMA 6 and IP 68 are commonly used.
In addition to protection from solids and liquids, enclosures are also rated for compatibility with explosive environments. ATEX and IECEX markings indicate the suitability of pressure switches and other electronic devices for hazardous applications. Before seeking an ATEX rating, it is crucial to accurately determine the type of hazardous area where the pressure switch will be used. Higher protection ratings can significantly increase the cost of the device, and a higher rating does not necessarily equate to better protection for a specific application.
Certifications ensure that a product meets the safety standards set by national and international organizations. This is particularly important for pressure switches used in applications impacting consumer health and safety, such as food manufacturing, fire protection, and flammable gas handling. Common certifications include Underwriters Laboratories (UL Listed or Recognized), CSA, FM, and CE, which are widely accepted and signify adherence to safety and quality standards.
Pressure switches serve two primary functions: maintaining the pressure or reservoir levels of a system, and protecting equipment from damage or inefficient operation.
This is a common application for pressure switches. In water pumps, pressure switches control the power to the motor. They activate the pump when the pressure drops below a set level and turn off the power once the desired pressure is reached.
Similar to water pumping systems, pressure switches in compressed air systems cut in power to the compressor motor when low pressure is detected. This helps maintain the proper pressure within the compressed air system.
In control systems utilizing pneumatic and hydraulic actuators, pressure switches regulate pumps and compressors to maintain reservoir pressure and levels.
In a refrigeration system, while the thermostat provides the control feedback signal by sensing the temperature in the cooled space, it does not monitor the equipment's state. A pressure switch acts as a safeguard, tripping the compressor motor in case of overpressure. It also protects against low-pressure conditions, which may indicate a refrigerant leak.
In a furnace or boiler, the pressure switch functions as a safety interlock, ensuring that the igniter does not operate if there is a problem with the draft system. This prevents the combustion chamber from running, avoiding incomplete combustion and potential safety hazards.
A differential pressure switch monitors the pressure drop across filters and screens. It triggers an alarm or notification when the pressure drop indicates that the filter is blocked or clogged, signaling that maintenance, cleaning, or replacement is needed.
Pressure switches have their roots in the 1800s, starting with the invention of the aneroid barometer by French scientist Lucien Vidie in 1843. Vidie's device used a spring balance to measure atmospheric pressure, with the spring's extension mechanically amplifying the measurement on an indicator system. Building on Vidie's work, Eugene Bourdon patented the Bourdon tube pressure gauge in 1849. This device, which remains in use today, was the first widely recognized mechanical pressure measurement instrument.
The Bourdon tube was later combined with a mercury switch, leading to the development of one of the earliest pressure switches. This innovation established the fundamental concept for electromechanical pressure switches, which integrate a sensing element like the Bourdon tube with a switching mechanism.
While the Bourdon tube pressure switch was groundbreaking, it had limitations. The Bourdon tube, being a tracing-type sensing element, had a shorter service life and struggled with pump ripple, surge pressure, vibration, and temperature fluctuations. Although using higher quality tubes could mitigate these issues, the cost of manufacturing remained high. This prompted the search for improved pressure switch designs.
In 1956, Roy Dunlap, recognizing the need for a reliable pressure switch for oil tanks, reached out to Ben Brown, a physics professor at the University of Kansas. Together, they developed the Static "O" Ring® pressure switch. This innovative design featured a force-balanced piston-actuated assembly sealed by a flexible diaphragm and a static o-ring. The diaphragm's response to fluid pressure counteracted the range spring's force, causing the piston shaft to move slightly and directly actuate the snap-action switching mechanism. The simplicity and durability of this design, combined with the static o-ring reducing wear and tear, led to successful manufacturing and sales. Roy Dunlap renamed the company to Static "O" Ring®, which eventually became SOR Inc.
Before 1930, mechanical pressure switches were the only available type. In that year, engineers began experimenting with transduction mechanisms, incorporating sensing device movements as part of electrical quantities. This marked the inception of the first pressure transducers. By 1938, engineers at the Massachusetts Institute of Technology and the California Institute of Technology independently developed bonded strain gauges. E.E. Simmons of Caltech was first to apply for a patent. The development of strain gauges was a pivotal step toward solid-state pressure switches, which were introduced widely in 1980 by Barksdale Inc. These early solid-state switches featured a bonded strain gauge sensor paired with a triac switch.
Today, solid-state pressure sensors are highly popular and advanced. They feature digital displays, offer both digital and analog outputs, and come with full programmability. Modern solid-state sensors can have one to four or more switch points, providing versatile control and monitoring options for various applications.
Although electronic pressure switches offer advanced features and greater flexibility, mechanical pressure switches still play a crucial role. One significant advantage of mechanical switches is that they do not require an external power source to operate. If power is lost, mechanical switches can still function by acting as a pair of contacts to make or break a circuit. This ensures reliability and safety in critical applications where power interruptions could otherwise lead to significant damage or harm.
Pressure switches are widely used as redundant safety measures across various industries. In situations where the primary instrument, such as a pressure transmitter, might fail or lose power, a mechanical pressure switch can act as a backup. By actuating when the setpoint is reached, mechanical switches provide an additional layer of safety. Their lower cost and independence from an external power supply contribute to a lower overall cost of ownership, which is a key reason for their continued use despite the advancements in electronic pressure switches.
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