Kayden CLASSIC 810 Thermal Flow, Level & Interface Switch

KAYDEN CLASSIC FLOW SWITCHES

BENEFITS

Reliability
Thermal dispersion flow switches are highly reliable and accurate, ensuring consistent protection for the pumps.

Maintenance
They require minimal maintenance, making them a cost-effective solution for long-term pump protection.

Versatility
Suitable for various types of fluids, including water, chemicals, and slurries.

• Ammonia Storage
• Biogas Flow
• Catalysis Vessels
• Chemical Injection & Additive Flow Monitoring
• Chemical Reactors
• Chlor-alkali Processes
• Compressors
• Condensers
• Cooling Water
• Deionization Tanks
• Digester Gas Flow
• Distillation Columns
• Drain Line Flow
• Emergency Eye Wash & Shower Stations
• Fermentation Vessels
• Flare Gas Monitoring
• Flare Knock-out Drums
• Flow Monitoring & Verification
• Heat Exchangers
• Heat Recovery Steam Generator (HRSG) - Power & Utilities
• High Pressure Flows
• Leak Detection
• Lube Oil Systems
• Monitoring Purge Air Flow
• Natural Gas to Boilers
• Oil Well System Testing
• Pumps
• Reboilers
• Refinery Flow Applications
• Relief Valve & Rupture Disk Flow Monitoring
• Remote Indication of Flow via Analog Output & Digital Communications
• Pump Protection - Dry Alarm
• Safety Spray Nozzle Monitoring
• Tank Blanketing
• Tank Overflow Protection
• Tanker Loading & Unloading
• Water & Wastewater
• Vaporizers
• Vent Monitoring

• Biogas Dehydration
• Blending Operations
• Carbon Slurry Level
• Compressor Scrubber
• Compressor Waste Liquid
• Condensate Receiver Tanks
• Cooling Tower Basins
• Crude Desalting
• Crude Dehydration
• Deionization Tanks
• Digester Blow Tanks
• Free Water Knock-out Tanks - High, Low and Interface Level
• Geothermal - Degasser Tanks
• Geothermal - Steam & Brine Separators
• Leak Detection (Accumulation Reservoir)
• Lime Slurry Level
• Mixing & Blending Systems
• Oil Separators & Treaters - High, Low & Interface Level
• Production Fluid Storage
• Pulp Bleaching Towers
• Pulp Digesters
• Pulp Storage
• Pulp Washing Systems
• Sampler Systems
• Sand Separators
• Scrubber Vessels
• Storage Tanks
• Sumps - All Types of fluids: Water, Oil, etc.
• Surge Tanks
• Tank Overflow
• Turpentine Recovery
• Vapor & Liquid Separation
• Vapor Recovery

• Crude Desalting
• Interface Control in Separation Vessels
• Interface Detection
• Interface Control & Level Detection in Settling Vessels
• Liquid-Liquid Extraction - LLX

• Liquids, Air & Gases
• Slurries
• Corrosive Liquids

• Flameproof, Hazardous & General-Purpose Areas

• Consistent Process Composition & Temperature
• Sufficient Straight Run Flow Profile (minimizes turbulence)
• Recommended Minimum of 5 Pipe Diameters from any Disturbance

Air & Gas

Thermal Dispersion Flow Switches for Pump Protection

In a wide range of industrial environments—from petrochemical processing and wastewater treatment to power generation and food & beverage production—pumps serve as vital components for fluid transfer and circulation. Ensuring their dependable and efficient performance is essential for maintaining throughput, product quality, and operational safety. However, conditions such as dry running, obstructed suction or discharge lines, and cavitation can cause substantial equipment damage, inflated maintenance costs, and compromised process integrity.

Thermal dispersion flow switches have proven to be effective tools for identifying these problematic scenarios early. By providing timely interlocks, they help prevent costly breakdowns. This paper offers a detailed exploration of how thermal dispersion flow switches operate, their advantages, considerations for choosing and installing them, and methods for integrating them into holistic pump protection protocols.

Thermal dispersion flow switches deliver a dependable, low-upkeep, and highly sensitive approach to preventing pump damage caused by low-flow or no-flow conditions. By harnessing the heat transfer principle, these devices are well-suited to harsh industrial settings and excel at detecting subtle flow changes. With the proper selection, careful installation, and integration into broader pump protection strategies, thermal dispersion flow switches significantly boost equipment reliability, lower maintenance expenses, and help maintain stable, safe, and productive fluid-handling operations.

1. Introduction
Safeguarding pumps is a critical factor in fluid handling within industrial applications. Pumps frequently operate under challenging conditions involving high pressures, corrosive or abrasive media, fluctuating temperatures, and varying flow profiles. These stressors can affect components such as seals and bearings. When a pump runs under no-flow or low-flow circumstances, or if a pipeline obstruction or closed valve impedes flow, the pump can overheat, cavitate, and ultimately fail.

While traditional mechanical flow sensors (like paddle switches or turbine meters) can detect flow interruptions, their moving parts introduce complexity, heighten maintenance demands, and reduce long-term reliability. In contrast, thermal dispersion technology leverages heat transfer rather than mechanical movement. These switches can reliably sense minimal flow rates, respond rapidly to changing conditions, and withstand harsh environments—making them well-suited for integrated pump protection strategies.

2. How Thermal Dispersion Flow Switches Work
A typical thermal dispersion switch incorporates two temperature sensors housed within a single probe that is inserted into the fluid. One sensor is slightly heated using a controlled current, while the other measures the ambient fluid temperature. The rate at which flowing fluid dissipates heat from the warmed sensor is proportional to the fluid’s mass flow or velocity.

When flow is restricted or absent, insufficient fluid passes by to cool the heated sensor, causing the temperature difference between the sensors to remain pronounced. Conversely, when fluid moves normally, the enhanced cooling effect reduces this temperature differential. By continuously tracking these changes, the switch can accurately determine when flow is present, critically low, or completely halted.

Key Advantages of Thermal Dispersion

No Moving Parts
Minimizes mechanical failures and maintenance needs.

High Sensitivity at Low Flow
Detects slight variations in flow rates, offering early indicators of dry-running conditions.

Rugged Construction
Withstands corrosive, abrasive, high-temperature, and high-pressure media.

Minimal Pressure Loss
The small sensor profile generates negligible flow resistance, preserving operational efficiency.

3. Pump Protection Scenarios and the Role of Flow Switches

3.1 Dry-Run Prevention
One of the most common pump failure modes occurs when the suction line is deprived of liquid—perhaps due to a closed valve, blocked inlet, vapor lock, or depleted feed tank. Running a pump without adequate fluid leads to overheating and damage to seals and bearings. By installing a thermal dispersion flow switch in the suction line, operators can detect a drop or absence of flow and deactivate the pump before it sustains heat-related harm.

3.2 Discharge Line Obstruction
If the discharge line becomes blocked or a downstream valve remains closed, pressure builds and flow decreases to negligible levels. Without adequate movement, the pump faces elevated temperatures and mechanical stress. A thermal dispersion switch placed downstream of the pump can identify reduced or zero-flow scenarios, prompting remedial actions such as opening a bypass line, adjusting valves, or shutting the pump down.

3.3 Low-Flow Conditions and Cavitation
Though thermal dispersion switches do not measure cavitation directly, early detection of reduced flow—especially under non-typical conditions—can help avert cavitation. By alerting operators to abnormal low-flow states, these switches enable timely intervention, whether it involves adjusting fluid parameters, altering valve positions, or activating safety interlocks.

4. Considerations for Selecting Thermal Dispersion Flow Switches in Pump Protection

4.1 Fluid Compatibility
The sensor’s wetted materials must endure the fluid’s corrosivity, particulate content, and temperature extremes. Common choices include stainless steel, titanium, and hastelloy C-276. Appropriate material selection ensures durability and reduces contamination risks.

4.2 Operating Conditions
The chosen switch must tolerate the system’s temperature and pressure envelopes. Verify that its maximum rated temperature and pressure aren’t exceeded. Thermal dispersion switches commonly support broad temperature ranges (from cryogenic conditions up to several hundred degrees Celsius) and high pressures (frequently above 100 bar, depending on the model).

4.3 Flow Sensitivity & Setpoints
Different processes and fluids demand distinct low-flow thresholds. The switch should allow for adjustable or pre-defined setpoints to differentiate normal variations from truly hazardous states. Carefully calibrating the alarm point ensures effective pump protection without frequent nuisance alarms.

4.4 Response Time
Match the switch’s reaction speed to your pump’s dynamics. In rapidly changing scenarios—like sudden valve closures or pump startup phases—faster response times are crucial. Many thermal dispersion switches offer adjustable time delays to prevent false trips from brief flow interruptions.

4.5 Sensor Placement and Mounting
Proper insertion length and orientation are essential for accurate flow detection. The sensor must be fully immersed in the fluid and located in a stable, representative flow region. Avoid placing it immediately after bends, valves, or fittings that create turbulence. Adhere to the manufacturer’s guidelines for recommended straight run lengths.

5. Installation and Commissioning Guidelines

5.1 Choosing the Right Spot
Position the flow switch in a section of pipe with stable, uniform flow. This may be downstream of the pump or upstream on the suction line, depending on the application (detecting no-flow at suction or discharge). Typically, maintain at least 10 diameters of straight pipe upstream and 5 downstream, though this can vary based on specific conditions and manufacturer recommendations.

5.2 Wiring and Integration
Thermal dispersion switches typically offer relay outputs or 4-20 mA signals. Integrate these into the pump’s control systems, interlocks, or a Distributed Control System (DCS). When a no-flow or low-flow threshold is reached, the switch can trigger pump shutdown, alarms, or valve adjustments. Ensure proper grounding, shielding, and compliance with any hazardous area requirements.

5.3 Calibration and Setpoint Validation
Follow the manufacturer’s instructions to set the trip threshold. Calibration often involves operating the pump under normal conditions and adjusting the switch so it triggers at the desired flow level. Some devices allow setpoint adjustments via onboard controls, software interfaces, or external instrumentation.

5.4 Regular Functional Checks
Although thermal dispersion switches are low-maintenance, periodic testing is advised for critical applications. Verify that alarms and shutdown sequences occur at the correct flow thresholds. If process conditions evolve—such as changes in fluid viscosity or temperature—recalibration may be necessary.

6. Integrating Flow Switches into a Comprehensive Pump Protection Plan

6.1 Redundancy and Layering
For especially critical pumps, consider adding redundant sensors. You can place multiple sensors in different locations or pipelines for increased reliability. Combine them with pressure, vibration, and temperature sensors, as well as motor current monitors, to form a robust pump health monitoring ecosystem.

6.2 Diagnostic and Data Capabilities
Modern thermal dispersion switches equipped with digital communication (e.g., MODBUS®) can deliver diagnostic data such as sensor health and drift detection. Feeding this information into a plant asset management system supports predictive maintenance and reduces unplanned downtime.

6.3 Compliance and Safety Standards
In hazardous environments, ensure that the chosen flow switch meets relevant safety and regulatory standards (e.g., CSA, UL, or CRN certifications). Models with intrinsically safe or explosion-proof designs are widely available.

7. Case Study

Scenario
A large chemical plant experienced repeated pump failures due to intermittent dry running during batch startups. Filters in the pump’s suction line occasionally became clogged, restricting flow.

Solution
Thermal dispersion flow switches were installed on each pump’s suction line and calibrated to trip slightly above the pump’s minimum flow requirement.

Results
Lower Maintenance Costs
Early pump shutdowns prevented damage from overheating and seal degradation.

Improved Operational Efficiency
Operators quickly identified and cleared clogged filters, reducing startup issues.

Enhanced Equipment Life
By preventing frequent dry runs, the pumps’ mean time between failures (MTBF) improved, lowering long-term costs.

References

ISA (International Society of Automation). “Pump Protection and Reliability Standards,” ISA Publications, 2020.
API (American Petroleum Institute) Standard 610, “Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries.”
Galvan, J., “Flow Switch Technology Review and Selection Guidelines,” Instrumentation & Control Magazine, Vol. 46, No. 3, 2021.
Cruz, P. and L. Martin, “Integrating Flow Measurement Devices in Pump Protection Schemes,” Chemical Engineering Progress, Vol. 117, No. 2, 2022.

Acknowledgements
The development of advanced thermal dispersion technology and its ongoing improvement are indebted to the research efforts of instrument manufacturers, industrial consortia, and standardization bodies dedicated to improving safety, efficiency, and reliability in industrial process operations.

Thermal Dispersion Flow Switches in Leak Detection Applications

Industrial processes and fluid transportation networks—ranging from pipelines carrying hydrocarbons to chemical supply lines feeding manufacturing processes—are vulnerable to leaks. Even minor leaks can cause serious safety risks, product loss, environmental damage, and regulatory non-compliance. Early and accurate detection of leaks is, therefore, a cornerstone of responsible and profitable operations. Among various leak detection technologies, thermal dispersion flow switches offer a uniquely effective solution for identifying subtle flow changes that may indicate a leak condition.

Thermal switches provide robust, low-maintenance performance even under challenging conditions. This paper details the principles of thermal dispersion flow technology, describes its strengths in leak detection scenarios, outlines factors for selection, installation, and integration, and provides a framework for using these switches as part of a comprehensive leak detection and mitigation strategy.

1. Introduction
Leak detection is critical across numerous industries:

Oil & Gas Pipelines
Preventing spills and reducing product losses ensures environmental protection and compliance with stringent regulations.

Chemical Processing Plants
Detecting leaks of hazardous chemicals protects worker safety, reduces clean-up costs, and prevents off-spec product.

Water and Wastewater Systems
Identifying minor leaks conserves resources, prevents contamination, and reduces infrastructure strain.

Food & Beverage and Pharmaceutical Lines
Ensuring product integrity and meeting quality standards by promptly identifying any fluid loss.

While leak detection has traditionally relied on volumetric balances, mass flow measurement, or pressure drop indicators, these methods often struggle to detect small, slow-onset leaks. Mechanical flow switches might fail due to fouling or wear in harsh environments. In contrast, thermal dispersion flow switches excel at detecting subtle deviations in flow conditions without relying on moving parts, thus offering improved reliability, lower maintenance, and heightened sensitivity to small flow disturbances.

2. Principles of Thermal Dispersion Technology

Thermal dispersion devices commonly use two sensors embedded in one insertion probe:

Heated Sensor
A small current is applied to this sensor, causing it to warm above the fluid’s ambient temperature.

Reference (Unheated) Sensor
This sensor measures the fluid’s temperature directly.

When the fluid flows around the probe, it removes heat from the heated sensor. The rate of heat removal correlates to the mass flow or velocity of the fluid. Under stable, leak-free conditions, the switch is calibrated to a known temperature differential representing normal flow. If a leak occurs downstream, the flow profile can change subtly. These changes manifest as variations in the temperature differential, which the switch can detect and use to trigger alarms or shutdowns.

Key Attributes Beneficial for Leak Detection

• High Sensitivity to Small Flow Changes
  Even slight flow reductions due to small leaks can be detected.
  
  
• No Moving Parts
  Minimizes maintenance and instrument drift, ensuring long-term stability and repeatability.
  
  
• Versatile Media Compatibility
  Suitable for liquids, gases, and slurries, allowing application across diverse industries.
  
  
• Robust Construction
  Resistant to corrosion, high pressures, and broad temperature ranges found in industrial lines.

3. Leak Detection Challenges and How Thermal Dispersion Addresses Them

3.1 Early and Subtle Leak Detection
Traditional monitoring techniques often rely on large flow variances or pressure drops to confirm a leak. By contrast, thermal dispersion flow switches can be set to detect small deviations in expected flow patterns. For example, if a petroleum pipeline experiences a small pinhole leak downstream, the overall flow at a measurement point may subtly fluctuate. The thermal dispersion switch, pre-calibrated to recognize normal flow conditions, will pick up on this subtle differential and trigger an alert.

3.2 Dirty, Corrosive, or Variable Fluid Conditions
Pipelines and process lines may carry viscous slurries, corrosive acids, dirty wastewater, or multiphase mixtures. Thermal dispersion probes are available in materials such as stainless steel, Hastelloy®, and other high-grade alloys to withstand harsh media. As they have no moving parts, there is no risk of mechanical jamming or sticking due to fouling. Thermal dispersion sensors also adapt well to fluid characteristic changes—density, viscosity, or temperature—as their calibration can account for these factors.

3.3 Minimal Pressure Drop and Unobtrusive Monitoring
Unlike inline flow meters or complex instrumentation, a thermal dispersion sensor’s small insertion probe offers minimal disturbance to the flow. This feature ensures that system efficiency is not compromised. The negligible pressure drop is crucial in large pipelines where maintaining flow efficiency is economically essential.

4. Selection Criteria for Thermal Dispersion Flow Switches in Leak Detection

4.1 Fluid Compatibility and Wetted Materials
Select materials that can withstand long-term exposure to the process fluid. Consider corrosion resistance, temperature rating, and any coatings that might enhance sensor longevity. Proper materials ensure minimal sensor drift and reduced maintenance intervals.

4.2 Measurement Range and Sensitivity
Determine the baseline or normal operational flow range. The chosen thermal dispersion switch should be capable of detecting slight deviations in this range. Because leak detection often hinges on very small changes, ensure the device provides fine resolution and adjustable setpoints.

4.3 Response Time and Stability
Leaks can develop slowly or occur suddenly. A thermal dispersion flow switch should have a response time suitable for the system’s dynamic characteristics. Many devices offer adjustable response delays to avoid nuisance alarms caused by transient disturbances (e.g., pump starts, valve adjustments).

4.4 Environmental and Safety Certifications
Check for necessary certifications, especially if the fluid is flammable, toxic, or explosive. Many thermal dispersion switches carry intrinsic safety or explosion-proof ratings (e.g., ATEX, IECEx, FM/CSA) to ensure compliance with industry regulations and safe operation in hazardous areas.

5. Installation and Commissioning Practices

5.1 Optimal Sensor Placement
Proper placement is crucial for effective leak detection. Consider the following guidelines:

• Upstream and Downstream Monitoring
  Placing switches at strategic pipeline intervals allows comparison of flow conditions at different points. A discrepancy between adjacent measurements can indicate a leak in the intervening segment.

Avoid Turbulence and Disturbances
Adhere to the manufacturer’s guidelines on straight-run pipe lengths. Typically, 10 diameters of straight pipe upstream and 5 downstream help ensure stable flow conditions and reliable readings.


5.2 Calibration to Baseline Conditions
Before commissioning, establish a baseline. Operate the system under known, leak-free conditions and record the stable temperature differential. Set alarm thresholds based on statistically significant deviations from this baseline, factoring in normal operational variances.

5.3 Integration with Control Systems
Thermal dispersion flow switches provide relay contacts, 4-20 mA signals, or digital communication outputs (e.g., HART®, Modbus®). Integrate these signals with a plant’s Distributed Control System (DCS) or Supervisory Control and Data Acquisition (SCADA) system.

In case of a suspected leak, the control system can:

• Trigger alarms or visual indicators.
• Initiate pump shutdown or valve adjustments to isolate the affected section.
• Notify operations and maintenance personnel for immediate inspection.
  
  

5.4 Periodic Verification and Maintenance
While thermal dispersion devices are low maintenance, periodic functional tests are recommended:

• Flow Simulations
  Temporarily modulate flow conditions to confirm that the switch triggers at the intended thresholds.
• Inspection for Fouling or Deposits
  Although rare, if the process fluid is heavily fouling, occasional cleaning may be beneficial to ensure optimal heat transfer characteristics.

6. Integration into a Comprehensive Leak Detection Strategy

6.1 Complementary Technologies
Thermal dispersion switches can be one element of a multi-layered leak detection solution. Integrating them with other techniques can enhance reliability and reduce false alarms:

• Pressure and Temperature Sensors
  Compare flow indications with pressure and temperature profiles to confirm or refute suspicions of leaks.
• Flow Meters and Mass Balances
  Use thermal dispersion switches as an early warning, supported by more complex flow meters for detailed quantification of leak rates.
• Acoustic Emission Detection
  Combine thermal dispersion detection with acoustic sensors that listen for the distinctive sound signatures of leaks.
  
  6.2 Alarming and Response Protocols
  Having a well-defined escalation procedure following a thermal dispersion alarm is critical.

Ensure that upon detection:

• Operators receive immediate notification.
• Automatic or semi-automatic isolation protocols can run, shutting valves or pumps to limit product loss.
• Incident reporting and root-cause analysis follow to prevent recurrence.

6.3 Regulatory Compliance and Environmental Stewardship
Leaking hazardous fluids poses environmental and safety risks. By detecting leaks early, thermal dispersion switches help operators meet stringent regulatory requirements (e.g., EPA, OSHA, local environmental laws) and uphold corporate social responsibility commitments. Early leak detection also aids in maintaining public trust and mitigating financial and reputational damage.

7. Case Study Example

Background
A petrochemical facility used a network of pipelines to distribute intermediate products between process units. Despite employing volumetric flow metering and pressure sensors, the facility occasionally failed to detect small leaks in a timely manner, resulting in product loss and concerns over soil contamination.

Solution
Thermal dispersion flow switches were installed at strategic intervals along the critical pipelines. Each switch was calibrated to a “normal” flow differential baseline. Any deviation beyond a small tolerance triggered an alarm in the control room.

Results
Early Leak Detection
The facility identified small leaks before they grew significant, reducing product loss and clean-up costs.

Enhanced Environmental Safety
Prompt isolation of leaking segments minimized the risk of environmental damage and regulatory penalties.

Operational Efficiency
Operators leveraged the early-warning capability of the thermal dispersion switches to schedule targeted maintenance, reducing unplanned downtime.

8. Conclusion
Thermal dispersion flow switches are a powerful tool in the arsenal of leak detection technologies. Their ability to detect subtle flow changes in challenging environments, combined with robust construction and low maintenance requirements, makes them invaluable for protecting personnel, preserving the environment, and ensuring operational excellence. By carefully selecting, installing, calibrating, and integrating these instruments into a broader leak detection strategy, organizations can significantly improve their capacity for early warning and swift response, ultimately reducing losses and maintaining regulatory and ethical standards in fluid handling operations.

References

API (American Petroleum Institute) RP 1130, “Computational Pipeline Monitoring for Liquid Pipelines.”
ISA (International Society of Automation). “Effective Leak Detection Systems and Best Practices,” ISA Publications, 2020.
ANSI/AWWA M36, “Water Audits and Loss Control Programs.”
Rathwell, G. and Liu, H., “Real-Time Leak Detection in Pipelines: Advances in Sensor Technology,” Journal of Pipeline Engineering, Vol. 15, 2022.
Cruz, P., “Integrating Non-Intrusive Flow Measurement Devices for Early Leak Warning,” Chemical Engineering Progress, Vol. 117, No. 5, 2022.

Acknowledgements
The ongoing development and refinement of thermal dispersion technology, as well as best practices in leak detection strategies, are the result of collaborative efforts by equipment manufacturers, standards organizations, and industry professionals dedicated to preserving safety, efficiency, and environmental integrity in fluid transport systems.