A Real Engineering Case on Temperature Limits, Explosion Protection and Safe Sensor Selection
Industrial environments containing combustible dust present unique engineering challenges. Selecting a hydraulic cylinder is no longer simply a matter of bore size, stroke length or operating pressure. Engineers must also evaluate explosion protection requirements, maximum surface temperature, sensor certification and material compatibility.
This real engineering case explains how the Vega Technical Department assisted a customer who needed to install hydraulic cylinders in an ATEX Zone 22 environment. During the technical evaluation, it was confirmed that the customer’s existing magnetic cylinder was a standard version with a maximum operating temperature of 80°C, while the MSU1 magnetic sensor complied with the ATEX requirements for the intended hazardous area. The analysis also confirmed that Zone 22 represents a relatively low explosion risk compared with other dust-classified zones.
Understanding ATEX Requirements
ATEX is the European regulatory framework governing equipment intended for use in potentially explosive atmospheres.
Its objective is to reduce the risk of ignition in environments where combustible gases, vapors or dust may be present.
Compliance with ATEX is mandatory for many industrial sectors, including:
- plastics processing;
- food production;
- pharmaceutical manufacturing;
- chemical processing;
- wood processing;
- grain handling;
- powder handling systems.
Selecting a hydraulic cylinder for these applications requires evaluating much more than hydraulic performance.
The cylinder, sensors and electrical accessories must all be compatible with the hazardous area classification.
The Customer’s Request
The customer contacted the Vega Technical Department because a new project required hydraulic cylinders suitable for an environment classified as ATEX Zone 22.
The application specified:
- Zone 22
- Maximum surface temperature: 155°C
- Equipment marking: CE Ex II 3D T155°C
The customer also provided the identification plate of a hydraulic cylinder previously used without operational problems and requested confirmation of its construction type and suitability for the new application.
Although the previous cylinder had operated successfully, the new installation required verification of both the cylinder characteristics and the magnetic sensor certification.
Why Previous Success Does Not Guarantee Future Compliance
One of the most common mistakes in industrial engineering is assuming that because a component worked correctly in one application, it will automatically be suitable for another.
ATEX compliance depends on many variables, including:
- hazardous area classification;
- maximum ambient temperature;
- surface temperature limits;
- ignition characteristics of the surrounding atmosphere;
- certification of electrical accessories.
For this reason, every new installation should be evaluated independently, even when the hydraulic cylinder itself appears identical.
The Temperature Limitation of Standard Magnetic Cylinders
During the technical investigation, the Vega Technical Department confirmed that the hydraulic cylinder previously supplied to the customer was a standard magnetic cylinder.
Because of its magnetic design, its maximum operating temperature was limited to 80°C.
This limitation is extremely important.
While the hydraulic cylinder may continue to function mechanically at higher temperatures, prolonged exposure can affect:
- magnetic field strength;
- sensor reliability;
- seal performance;
- lubricant characteristics;
- overall service life.
For this reason, operating temperature must always be verified during the design stage rather than after installation.
Selecting ATEX-Certified Magnetic Sensors
Although the standard magnetic cylinder had an operating temperature limit of 80°C, the investigation confirmed that the MSU1 magnetic sensor complied with the applicable ATEX requirements for the customer’s hazardous environment.
This distinction is particularly important.
A hydraulic cylinder and its magnetic sensor are two different components.
Each component may have different certification requirements depending on its function.
When designing hydraulic systems for hazardous areas, engineers must verify that every electrical device—including magnetic sensors—is certified for the intended ATEX classification.
Ignoring this requirement may compromise both regulatory compliance and plant safety.
What Does ATEX Zone 22 Mean?
The technical review also confirmed that the application belonged to ATEX Zone 22, which represents the lowest level of explosion risk among dust-classified hazardous areas.
Zone 22 is defined as an area where a potentially explosive dust atmosphere is not likely to occur during normal operation, and if it does occur, it exists only for a short period.
Typical examples include:
- dust collection systems;
- packaging equipment;
- powder transfer stations;
- certain plastic processing operations;
- storage areas where combustible dust may occasionally be released.
Although the probability of an explosive atmosphere is relatively low, equipment installed in these environments must still satisfy the applicable ATEX requirements.
Why Temperature Is a Critical Design Parameter
Many engineers focus primarily on hydraulic pressure when selecting a cylinder.
However, temperature is often equally important.
Operating temperature influences:
- seal life;
- lubricant viscosity;
- magnetic sensor stability;
- permanent magnet performance;
- dimensional expansion of mechanical components.
A hydraulic cylinder that performs perfectly at 40°C may require different materials, seals or sensors when operating close to its maximum allowable temperature.
For this reason, thermal conditions should always be evaluated during the design phase rather than after commissioning.
Understanding the Equipment Marking: CE Ex II 3D T155°C
One of the most important aspects of the customer’s request was the equipment marking specified for the installation:
CE Ex II 3D T155°C.
Although this marking may appear complex, each element provides essential information about the equipment’s intended operating environment.
CE indicates compliance with the applicable European regulations.
Ex identifies equipment designed for use in potentially explosive atmospheres.
Group II refers to equipment intended for industries other than underground mining.
Category 3D specifies equipment suitable for environments where explosive dust atmospheres are unlikely during normal operation but may occur occasionally, corresponding to Zone 22.
Finally, T155°C indicates that the maximum external surface temperature of the equipment must not exceed 155°C under specified operating conditions.
Understanding these markings is essential during the design phase because selecting equipment with an incorrect certification may compromise both plant safety and regulatory compliance.
Stainless Steel Does Not Automatically Mean ATEX
During the technical discussion, it was mentioned that the customer intended to purchase stainless steel hydraulic cylinders.
This highlights another common engineering misconception.
Many engineers assume that using stainless steel automatically makes a hydraulic cylinder suitable for hazardous environments.
In reality, the material itself is only one element of the overall design.
ATEX compliance depends on many additional factors, including:
- electrical accessories;
- magnetic sensors;
- maximum surface temperature;
- ignition risk;
- equipment certification.
A stainless steel cylinder may offer superior corrosion resistance, but it is not automatically ATEX certified simply because of its material.
Each component of the hydraulic assembly must be evaluated individually.
Why Temperature Matters More Than Many Engineers Realize
Temperature affects far more than the mechanical strength of a hydraulic cylinder.
As operating temperatures increase, several components may gradually approach their design limits.
These include:
- elastomer seals;
- permanent magnets;
- magnetic sensors;
- lubricants;
- cable insulation;
- electronic components.
Even if the cylinder body remains structurally sound, one of these secondary components may become the limiting factor for the entire hydraulic assembly.
For magnetic cylinders in particular, elevated temperatures may reduce magnetic field strength, making position detection less reliable.
This is precisely why the Vega Technical Department confirmed that the customer’s existing magnetic cylinder had a maximum operating temperature of 80°C despite being mechanically suitable for many industrial applications.
Common Mistakes When Selecting Hydraulic Cylinders for ATEX Applications
Technical support departments frequently encounter the same design mistakes when customers specify hydraulic cylinders for hazardous environments.
Among the most common are:
- assuming that every magnetic sensor is ATEX certified;
- selecting cylinders based only on pressure and stroke;
- overlooking maximum operating temperature;
- confusing stainless steel construction with ATEX compliance;
- assuming that equipment previously used in another installation is automatically suitable for a new hazardous area;
- failing to verify the certification of every electrical accessory connected to the hydraulic system.
These errors rarely originate from poor engineering practices.
Instead, they usually result from incomplete information during the early stages of machine design.
Engineering Recommendations
When designing hydraulic systems intended for hazardous environments, engineers should adopt a systematic evaluation procedure.
The Vega Technical Department generally recommends verifying:
- hazardous area classification;
- ambient operating temperature;
- maximum permitted surface temperature;
- cylinder operating temperature limits;
- seal material compatibility;
- magnetic sensor certification;
- electrical connector suitability;
- cable specifications;
- maintenance accessibility.
Considering these parameters at the design stage significantly reduces the risk of costly modifications after commissioning.
Lessons Learned from This Engineering Case
This technical support case demonstrates that selecting a hydraulic cylinder for an ATEX application requires much more than checking pressure ratings or dimensional compatibility.
The customer’s previous installation had operated successfully for years.
However, before approving a new application, the Vega Technical Department reviewed both the operating temperature and the hazardous area classification.
The investigation confirmed that:
- the existing magnetic hydraulic cylinder had a maximum operating temperature of 80°C;
- the MSU1 magnetic sensor complied with the required ATEX certification;
- the application corresponded to ATEX Zone 22, representing a relatively low dust explosion risk.
This engineering verification allowed the customer to make an informed decision based on technical data rather than assumptions.
Engineering Conclusions
Hydraulic cylinders used in hazardous environments must be selected using a comprehensive engineering approach.
Pressure capacity, bore diameter and stroke length remain important design parameters, but they represent only part of the selection process.
Hazardous area classification, operating temperature, surface temperature limits and the certification of magnetic sensors are equally critical.
This real engineering case illustrates the importance of reviewing every component of the hydraulic system before installation.
By confirming the operating temperature limitations of the existing magnetic cylinder, verifying the ATEX certification of the MSU1 sensor and evaluating the requirements for Zone 22, the Vega Technical Department helped the customer avoid potential compliance issues while ensuring safe operation.
The most important lesson is simple:
ATEX compliance is never determined by a single component. It results from the correct combination of certified equipment, suitable operating conditions and sound engineering design.
