In the field of industrial automation, liquid level detection is one of the most fundamental and critical aspects of process control. Particularly in applications involving flammable or explosive media, liquid level switches not only perform the function of “measurement” but also directly impact plant safety, personnel safety, and the stable operation of the entire production system. Among the many point-type level detection instruments, fork-type level switches are widely used in various industrial settings due to their mature design, clear operating principles, and excellent long-term stability.

However, with the rapid development of industries such as petrochemicals, coal chemicals, fine chemicals, and energy storage and transportation, production processes are increasingly moving toward higher automation, higher energy density, and greater risk. Consequently, the limitations of standard fork-type level switches in explosive hazardous areas have gradually become apparent. It is against this backdrop that explosion-proof fork-type level switches have become indispensable equipment in industrial settings.

I. Working Principle and Basic Applications of Fork-Type Level Switches

Tuning fork level switches are typical point-level detection instruments, and their core principle is based on detecting changes in mechanical vibration characteristics. When the tuning fork is in air or a gaseous environment, its vibration frequency remains stable; when covered by liquid or a high-density medium, the vibration is dampened, causing significant changes in frequency and amplitude. The electronic module uses these changes to determine whether the medium has reached the set level and outputs a stable switching signal.

Since fork-type level switches rely on changes in mechanical vibration states for detection, their measurement mechanism is independent of the medium’s conductivity, dielectric constant, color, or transparency, and does not require any calibration or compensation for the medium. Additionally, these instruments demonstrate strong adaptability to common on-site conditions such as foam buildup, liquid surface fluctuations, agitation, and process pressure variations, exhibiting outstanding stability and repeatability.

For these reasons, fork-type level switches have been widely and extensively used in various industrial process control scenarios. Typical industries include: Water Resources and Environmental Engineering: Used for high/low level alarms and interlock control in reservoirs, tanks, and wastewater treatment units

Chemical Process Level Control: Suitable for process points such as reactors, buffer tanks, and intermediate storage tanks

Food and beverage production: Meeting requirements for hygiene, reliability, and continuous operation

Pharmaceutical and biotechnology: Suitable for applications with high demands on process stability and equipment consistency

General industrial storage tanks and vessels: Used for limit detection and overflow protection of various liquid media

In non-explosive environments, standard fork-type level switches are capable of meeting the requirements of most operating conditions, demonstrating advantages such as stable performance, high reliability, and low maintenance.

II. Special Requirements for Level Detection in Explosive Hazardous Environments

In industrial settings involving flammable and explosive media—such as the storage and transportation of crude oil, gasoline, solvents, LNG, alcohol, and light hydrocarbon chemicals—the on-site environment often exhibits the following characteristics:

△ The prolonged presence of flammable and explosive gases or vapors

△ Frequent equipment start-ups and shutdowns, where static electricity and transient energy cannot be ignored

△ Extremely high requirements for the electrical safety rating of instruments

△ Strict safety regulations and certification systems

In such environments, any equipment capable of generating electrical sparks or high-temperature surfaces may serve as a potential ignition source for an explosion. Standard vibrating fork level switches, which lack explosion-proof design and certification, fail to meet relevant safety standards and pose serious application risks; therefore, their use is strictly restricted or prohibited.

1. Intrinsically Safe (Ex ia)

The core principle of intrinsically safe explosion protection is energy limitation. Through circuit design, voltage, current, and stored energy are strictly limited to levels below safe thresholds, ensuring that even under normal operating conditions or in the event of a single fault, the energy released is insufficient to ignite an explosive mixture.

Features include:

△ Suitable for high-risk areas such as Zone 0 and Zone 1

△ High safety level and low system-level risk

△ Requires use with intrinsically safe power supplies or safety barriers

2. Flameproof Type (Ex d)

Flameproof enclosures completely encapsulate components that may generate sparks or high temperatures within a high-strength metal housing. Even if an explosion occurs inside, neither flame nor energy is transmitted to the external environment.

Features include:

△ Robust construction with strong environmental resistance

△ Suitable for applications with high mechanical stress

△ Requires strict adherence to installation and maintenance standards

IV. Expanding the Scope of Application for Explosion-Proof Fork-Type Level Switches

• Intrinsically Safe Explosion-Proof (Gas):

Ex ia IIC T1…T6 Ga

By strictly limiting the energy of the electrical circuit, the equipment is incapable of igniting explosive gas mixtures under both normal operating conditions and specified fault conditions. Suitable for high-risk areas such as Zone 0 and Zone 1.

• Flameproof Explosion-Proof (Gas):

Ex db IIC T6…T1 Gb

Utilizing a high-strength flameproof enclosure structure, components capable of generating sparks or high temperatures are completely sealed. Even if an explosion occurs internally, energy will not be transmitted to the hazardous external environment. Suitable for Zone 1 and Zone 2 areas.

• Gas/Dust Dual-Protection Type:

Ex db IIC T6…T1 Gb + Ex tb ⅢC T440℃…T80℃ Db

Meets safety requirements for both explosive gas and combustible dust environments, making it suitable for petrochemical, coal chemical, energy storage and transportation applications, as well as complex operating conditions where dust accumulation is a risk.

Through combined certification for multiple explosion-proof types, the Ring-11 explosion-proof fork-type level switch covers a wider range of hazardous area classifications and media types, providing greater flexibility in selection and system safety redundancy for engineering design.

Users can flexibly select the appropriate explosion-proof type based on the risk level of the operating conditions, system architecture, and on-site regulations.

On this basis, the application scope of the explosion-proof fork-type level switch has been significantly expanded. Typical scenarios include, but are not limited to:

• Storage tanks for crude oil, refined oil, and chemical liquids

• Tank farms for gasoline, diesel, and lubricating oil

• LNG (liquefied natural gas) storage and transportation pipelines

• Reactors and buffer tanks containing flammable solvents

• High-risk level interlock points in petrochemical plants

In these applications, explosion-proof fork-type level switches not only perform level detection functions but also frequently serve as critical components of safety interlock systems, directly participating in safety control logic such as overflow prevention, dry-run prevention, and leak detection.

V. Engineering Value and Long-Term Operational Advantages

From an engineering application perspective, the value of explosion-proof fork-type level switches lies not only in their ability to operate in hazardous areas, but also in their long-term performance:

• Simple detection mechanism with strong interference resistance

• Low correlation with medium characteristics, resulting in a wide range of applications

• Clear output signals, facilitating integration with DCS/SIS systems

• Long maintenance intervals, reducing total lifecycle costs

In modern industrial environments that emphasize intrinsic safety, system reliability, and compliant operation, explosion-proof fork-type level switches have evolved from “optional equipment” to a standard component in many high-risk processes.