Will sealed liquid level sensors leak when used in coal mines?

Using sealed liquid level sensors in coal mine applications does not necessarily mean leakage will occur. The key factors are product structure, installation method, medium characteristics, and on-site maintenance standards. Underground coal mines commonly have high humidity, high dust concentrations, frequent equipment vibration, localized corrosive media, and temperature fluctuations. If the sealing design of a liquid level measurement device is inadequate, problems such as water ingress, liquid seepage, moisture in the wiring chamber, or measurement drift can indeed occur.

For drainage pump stations, water sumps, emulsion tanks, sedimentation tanks, chemical dosing equipment, and mine wastewater treatment systems, liquid level data is directly related to automatic drainage, equipment interlocking, and safe operation. Selecting a liquid level transmitter with a reliable protection rating suitable for coal mine operating conditions, and properly controlling vulnerable points such as threads, flanges, lead wires, and junction boxes during installation, can significantly reduce the risk of leakage and failure.

Relying on the production base of its subsidiary, Shaanxi Qinkong Sensor Technology Co., Ltd., Xi'an Shenghongchuang Instrumentation Co., Ltd. can provide liquid level transmitters and supporting intelligent digital display control instruments for industrial automation measurement and control systems. For humid, dusty, and vibration-prone conditions such as coal mines, selection should be based on the actual medium, pressure range, installation depth, power supply conditions, and signal connection method, rather than solely on “waterproof” parameters.

I. Where Leakage Usually Occurs in Coal Mine Liquid Level Measurement

1. The sensor body is not the only risk point

Common leakage risks in coal mine liquid level sensors may not occur in the pressure-sensing element itself, but more often at the cable outlet, junction box cover, threaded connection, flange gasket, pressure-guiding interface, and damaged cable locations. In particular, when submersible liquid level transmitters remain immersed in water sumps or sewage pools for long periods, the connection between the cable and housing must withstand water pressure, tensile force, and repeated bending, making it a key inspection area.

For example, when the installation depth reaches 10 meters, the external hydrostatic pressure on the sensor is approximately 0.1MPa. If the water level is deeper, the pressure borne by the housing, cable sealing end, and venting structure will also increase accordingly. Ordinary low-quality potting processes may perform normally in short-term tests, but after several months of immersion, vibration, and temperature cycling, tiny water seepage paths may develop, resulting in reduced internal insulation.

For liquid level measurement solutions with pressure-guiding tubes or external flanges, the gasket material must not be overlooked. Mine water may contain suspended solids, salts, oil contamination, or mildly corrosive components. If the gasket has insufficient medium resistance, it may harden, expand, or deform under pressure, ultimately affecting the contact quality of the sealing surface.

2. Humidity, dust, and vibration can magnify weak points

Humid air in coal mine environments can easily enter junction boxes and cable connectors that are not properly tightened, causing condensation. Even without obvious liquid leakage, long-term condensation may cause terminal oxidation, signal fluctuations, and reduced insulation resistance, appearing as fluctuating liquid level readings, unstable output current, or communication interruption.

Coal dust has strong adhesion properties. When it accumulates in junction box sealing rings, flange sealing surfaces, or gaps in mounting brackets, it may prevent seals from being fully compressed. Continuous vibration generated during equipment operation can gradually loosen threaded connections without anti-loosening measures. Special attention should be paid to areas near pump units, belt conveying zones, and locations with concentrated mechanical equipment.

Therefore, the reliability of coal mine liquid level sensors cannot be judged solely by a single IP rating. IP68 generally indicates strong dustproof and continuous immersion protection capabilities, but actual projects must still verify whether the immersion depth, continuous immersion time, cable structure, wiring method, and on-site protection measures conform to the product's technical specifications.

Common Sealing Risks and Key Handling Measures in Coal Mines

II. What Type of Sealed Liquid Level Sensor Is More Suitable for Coal Mines?

1. First confirm whether the measurement method is suitable for the site

Submersible hydrostatic liquid level transmitters are commonly used in coal mine water sumps, clean-water tanks, and drainage wells. These products are relatively straightforward to install and can calculate liquid level height through liquid-column pressure, making them suitable for continuous liquid level monitoring. For common measuring ranges such as 0 to 5 meters, 0 to 10 meters, and 0 to 20 meters, an appropriate margin should be reserved to avoid the measurement burden caused by long-term full-scale operation.

If the medium contains large amounts of sand, coal slurry, or floating debris, the sensor probe should not be placed directly on the bottom of the tank. A certain distance should normally be reserved from the tank bottom to reduce the likelihood of sediment covering the pressure-sensing diaphragm. For viscous, scaling-prone, or highly corrosive liquids, diaphragm material, installation location, and subsequent cleaning conditions must be evaluated.

In sealed vessels, pressurized storage tanks, or applications where gas pressure above the liquid surface changes, measuring only the bottom pressure may not accurately reflect the actual liquid level. For such conditions, a differential pressure liquid level measurement solution may be considered. By simultaneously obtaining pressure at the bottom and top of the vessel, the influence of gas-phase pressure on liquid level results can be eliminated.

2. Sealing materials must match the medium and temperature

In conventional mine water and general industrial wastewater environments, stainless steel housings offer good mechanical strength and corrosion resistance, enabling them to withstand routine impacts and long-term immersion. For liquids containing acids, alkalis, or special chemical components, they cannot simply be treated uniformly as “wastewater”; 316L stainless steel, PTFE, or other corrosion-resistant wetted materials should be selected based on the medium composition.

PTFE has strong resistance to many strong acid and strong alkali media, but its mechanical support method, installation stress, and temperature conditions must still be verified in conjunction with the product structure. If the on-site liquid temperature remains above 60℃ for extended periods, or if there are obvious hot-cold cycles, the temperature resistance range, elasticity degradation, and thermal expansion and contraction effects of sealing components should all be included in the evaluation.

High-quality liquid level sensors should undergo precision machining, calibration, and finished-product testing. For coal mine projects, in addition to accuracy class, the supplier should clearly specify the product protection rating, pressure resistance, wetted material, cable length, power supply range, and output type to avoid later rework caused by incomplete information.

Reference for Coal Mine Liquid Level Sensor Selection

III. Even the Best Sealing May Fail If Installation Is Inadequate

1. The cable and vent end must be properly protected

Submersible liquid level transmitters typically compensate for atmospheric pressure through an air-venting structure inside the cable to ensure accurate liquid level measurement. During installation, the cable end should not be directly exposed to standing water, dripping water, or high-humidity enclosed spaces; otherwise, moisture may enter along the vent path, causing zero-point deviation or moisture damage to electronic components.

It is recommended to install wiring terminals in a dry location that is convenient for inspection, using sealed junction boxes and waterproof cable glands. Cable routing should avoid sharp edges, vehicle traffic areas, and locations subject to strong pulling forces. When cable length exceeds 30 meters, attention should also be paid to cable fixing intervals and signal anti-interference measures.

In areas with strong electromagnetic interference from frequency converters, motors, pump units, and similar equipment, 4-20mA signals provide good anti-interference performance and are suitable for long-distance analog signal transmission. If RS485 communication is used, shielded twisted-pair cable should be used with proper grounding. In conventional projects, communication distances can reach several hundred meters, but the specific distance should still be determined according to cable quality, baud rate, number of nodes, and the level of on-site interference.

2. Installation location determines sensor service life

The sensor should be prevented from falling directly into sediment and should not remain close to pump inlets or areas subject to strong water-flow impact for long periods. Water-flow impact can generate instantaneous pressure fluctuations that affect the stability of liquid level readings, while vibration caused by pump starting and stopping may also accelerate fatigue in cables and mounting brackets. A more appropriate approach is to install a fixed guide tube or suspension point in a relatively stable measurement area.

For tanks with obvious liquid level fluctuations, appropriate filtering or delay can be set in the control system to prevent short-term surface disturbances from causing frequent pump starts and stops. However, the filtering time should not be too long, as this may reduce the response speed of high-level alarms. Actual settings should be adjusted according to tank capacity, inflow rate, and drainage capacity.

After installation, zero point, full scale, or comparative liquid level verification should be performed, and the initial output value should be recorded. For example, a product with 4-20mA output should be close to 4mA near 0% liquid level and close to 20mA near 100% of the measuring range. Including initial data in the equipment records helps identify gradual drift, water ingress, or cable faults during subsequent operation.

IV. How to Reduce Leakage Risks Through Maintenance in Coal Mine Applications

1. Establish periodic inspection items

Coal mine liquid level measurement devices should be periodically inspected in conjunction with equipment maintenance schedules. Daily checks can include whether display values are stable and whether control instruments have abnormal alarms. Monthly checks can cover junction box sealing, cable sheathing, mounting brackets, and threaded connections. During concentrated maintenance of the drainage system, further inspection should be conducted to determine whether the probe surface has coal slurry adhesion, scale buildup, or mechanical damage.

If the liquid level display remains unchanged for a long period, fluctuates frequently, or the output remains below 3.6mA or above 21mA, first check the power supply, wiring, PLC analog input channel, and communication line before inspecting the sensor body. A sensor leak should not be determined directly based only on an abnormal display, so as not to overlook actual issues such as loose control cabinet terminals or damaged cable sheathing.

If probe contamination is found, it should be cleaned using a method compatible with the material, avoiding the use of hard tools to scrape the pressure-sensing diaphragm. For corrosive medium applications, maintenance personnel should also confirm protective equipment, shutdown isolation, and pressure-relief conditions to ensure that maintenance procedures comply with on-site safety management requirements.

2. Support project acceptance with complete technical documentation

When purchasing coal mine liquid level sensors, it is recommended that the model, measuring range, accuracy, supply voltage, output signal, wetted material, protection rating, process connection method, and cable length be included in the technical agreement. For projects requiring connection to a PLC, digital display meter, or remote monitoring platform, it is also necessary to confirm in advance whether 4-20mA, 1-5V, RS485, RS232, or other protocol interfaces are compatible.

1-5V liquid level sensors can maintain relatively stable output under stable power supply, standardized wiring, and controllable interference conditions, but they are more susceptible to line voltage drop and electromagnetic environments during long-distance transmission. By comparison, 4-20mA signals facilitate the identification of cable break faults, while RS485 is suitable for multi-point networking and digital data acquisition. The specific choice should be based on the control system architecture.

Reliable industrial sensing and measurement-control products must not only meet initial measurement accuracy requirements but also provide long-term operational stability. Choosing a supplier with production, calibration, testing, and technical service capabilities can provide more targeted support during product selection, installation guidance, parameter commissioning, and fault handling, reducing downtime and maintenance costs caused by improper selection on site.

V. Conclusion: Leakage Prevention for Sealed Liquid Level Sensors in Coal Mines Should Be Addressed Systematically

Whether sealed liquid level sensors will leak in coal mine use cannot be answered simply with “yes” or “no.” Selecting a measurement solution suitable for mine water, coal slurry water, or pressurized vessels, using reliable housing, cable potting, and wiring sealing structures, and strictly implementing installation and maintenance requirements can effectively control the risks of leakage, moisture ingress, and signal distortion.

For ordinary drainage water sumps, focus should be placed on immersion protection, the cable vent end, and vibration-resistant installation of submersible liquid level transmitters. For corrosive liquids, priority should be given to verifying wetted materials and the medium resistance of sealing components. For sealed tanks, differential pressure liquid level measurement structures should be evaluated first to avoid the influence of vessel pressure changes on liquid level assessment.

Before determining a coal mine liquid level measurement project solution, on-site information such as medium name, liquid level range, installation depth, temperature, pressure, power supply method, PLC interface, and protection requirements can be compiled and submitted to professional technical personnel for targeted selection. Xi'an Shenghongchuang Instrumentation Co., Ltd. can provide liquid level transmitters, supporting control instruments, and non-standard measurement and control solution support according to actual operating conditions, helping projects establish stable and reliable liquid level monitoring and interlocking control systems.