KNOWLEDGE CENTER

Pilot valves and operators ATEX related questions ATEX maintenance

IEC - Functional safety IECEx

Are 316 stainless steel bodied solenoid valves equipped with all internal parts in 316 stainless steel?

No, 316 stainless steel is a nonmagnetic material, but parts like core and plug nut must be ferromagnetic compatible, otherwise the valve doesn't work. ASCO Numatic's core and plug nut material is a made of special chemical high compatible ferromagnetic stainless steel.

Are SIL approved solenoid valves suitable for different conditions (temperature/medium)?

No, please refer to conditions indicated on the certificate.

Can I use pilot operated valves on 3-15 psi signal?

Theoretically not, a pilot operated valve requires a minimum operating pressure sometimes higher than a pneumatic signal. Only an externally piloted valve can be used, applying auxiliary air.

Can I, a maintenance engineer, simply replace a coil under the ATEX directive?

Yes, for NF and NL (EEx d), EM (EEx em), etc. solenoid operators a revision kit is available.
However, the PV (EEx m) coil has to be ordered with the old order (catalogue) number as the catalogue number of the valve is also stated on the coil and this ensures the traceability of the repaired ATEX product.

How does manual reset NVR (No voltage release) tamperproof operate?

With the coil energized and by activating the manual reset the valve will switch position. The coil has to be de-energized to trip in a safe position. The Tamperproof function guarantees no pressure/flow on exit in case of reset and coil de-energized.

Should older solenoid valves also be ATEX classified in 2006? Do I have to replace them all?

For dust-filled atmospheres: the existing working premises must be adapted to comply with the directive before July 1, 2006.

For gaseous atmospheres: installed equipment which does not comply with Directive 94/9/EC must have been assessed by the site manager. Depending on the risk analysis, the manager decides whether or not it is necessary to upgrade it to comply with Directive 94/9/EC. Equipment which has received a positive assessment can be maintained in service. In that case, you can use your equipment in stock to replace any defective equipment if it complies with the former CENELEC regulations.

What are the lubrication needs for the series 551 spool valves?

No additional lubrication is needed for series 551 valves

Which type of Intrinsically Safe operators can I easily choose?

The IS operator is related to the IS barrier or remote I/O used. We suggest contacting your local ASCO Numatics technical advisor for a correct choice.

IEC - Functional safety

Can I use IEC 61508 as a standalone standard?

Yes. A major objective of the standard is to enable the development of E/E/PE safety-related systems where application sector international standards do not exist. It is also possible that the application sector standards will refer the user to requirements of IEC 61508.

• emergency shut-down systems,
• fire and gas systems,
• turbine control,
• gas burner management,
• dynamic positioning (control of a ship's movement when in proximity to an offshore installation),
• railway signaling systems (including moving block train signaling),
• crane automatic safe-load indicators and
• machinery guard interlocking systems.

 

Relevant means of implementing safety functions include electro-mechanical relays (i.e. electrical), non-programmable solid-state electronics (i.e. electronic) and programmable electronics. Programmable electronic safety-related systems typically incorporate programmable controllers, programmable logic controllers, microprocessors, application specific integrated circuits, or other programmable devices (for example) In every case, the standard applies to the entire E/E/PE safety-related system (for example from sensor to actuator, including human operators where relevant). For safety functions to be effectively specified and implemented, it is essential to consider the system as a whole.

Do I have to use third party certified components in order to comply with IEC 61508?

No. The standard requires that a functional safety assessment is carried out on all parts of the E/E/PE safety-related system and for all stages of the lifecycle (see clause 8 of IEC 61508-1).

The level of independence required of the assessor ranges from an independent person in the same organization for safety integrity level 1 to an independent organization for safety integrity level 4. The required level of independence for safety integrity levels 2 and 3 is affected by additional factors including system complexity, novelty of design and previous experience of the developers. There is also a specific requirement that the assessor shall be competent for the activities to be undertaken.

How does IEC 61508 fit together with application sector standards?

The standard sets out a generic approach for all safety lifecycle activities for E/E/PE safety-related systems that are used to perform safety functions. This unified approach has been adopted in order that a rational and consistent technical policy is developed for all E/E/PE safety-related systems, irrespective of the application sector. A major objective is to facilitate the development of standards and guides for application sectors and specific subsystems and components. For this reason the first four parts of the standard are basic safety publications.

What application sector standards based on IEC 61508 are there?

There are currently no fully published application sector standards. In development are IEC 61511 for the process sector, IEC 61513 for the nuclear sector and IEC 62061 for the machinery sector.

• human actions or errors that can place a demand on the E/E/PE safety-related protection system;
• human failure to respond effectively to alarms or take other actions which would otherwise reduce the demand on the E/E/PE safety-related protection system;
• human failure in testing and maintenance of the E/E/PE safety-related protection system, reducing its effectiveness and increasing the probability of failure on demand.

 

Suppliers are quoting that their products conform to IEC 61508 for a specific Safety Integrity Level (SIL). Does this mean that using these products is sufficient for me to comply with IEC 61508?

No. A safety integrity level is not directly applicable to individual subsystems or components. It applies to a safety function carried out by the E/E/PE safety-related system.

IEC 61508 covers all components of the E/E/PE safety-related system, including field equipment and specific project application logic. All these subsystems and components, when combined to implement the safety function (or functions), are required to meet the safety integrity level target of the relevant functions. Any design using supplied subsystems and components that are all quoted as suitable for the required safety integrity level target of the relevant functions will not necessarily comply with the requirements for that safety integrity level target. A simple example is when the subsystem or component is incorrectly installed.

Important factors to be quoted by the supplier are the rate of unrevealed (i.e. not detected by the on-line diagnostic tests) dangerous failures and the diagnostic test interval (needed to ensure that a safe reaction to revealed dangerous failures can be achieved quickly enough).

What does the IEC 61508 cover?

IEC 61508 applies to safety-related systems when one or more of such systems incorporate electrical and/or electronic and/or programmable electronic (E/E/PE) devices. It covers possible hazards caused by failure of the safety functions to be performed by the E/E/PE safety-related systems, as distinct from hazards arising from the E/E/PE equipment itself (for example electric shock etc). It is generically based and applicable to all E/E/PE safety-related systems irrespective of the application.

It is recognized that the consequences of failure could also have serious economic implications and in such cases the standard could be used to specify any E/E/PE safety-related system used for the protection of equipment or product.

What is a failure rate?

A failure rate is the conditional probability per units of time that the component/system fails in (t+dt), given that it is good in t. It is often a constant, but can assume different values depending whether the incorrect functioning is fail safe or fail danger.

What is a repair rate?

The repair rate is the conditional probability per units of time that the component/system becomes good in (t+dt), given that it is failed in t. It is often a constant.

What is functional safety?

A system is defined functionally safe if random, systematic and common cause failures do not lead to malfunctioning of the system and do not result in Injury or death of humans, spills to the environment, and loss of equipment or production. Functional safety deals with that part of the overall safety that depends on the correct functioning of the safety-related system.

What is Mean (Productive) Time Between Failure (MTBF)?

The MTBF is the average time (hours) the equipment performed its intended function between failures; productive time divided by the number of failures during that time. Using MTBF therefore, requires that the user not only has the capability of capturing failure information, but also tracking and categorizing total time accurately.
MTBF= Productive time / # of failures
To increase MTBF means that reliability and customer satisfaction are also increased
MTBF = MTTR + MTTF

What is Mean Time To Failure (MTTF)?

The MTTF is the mean necessary time for a component/system to fail since the beginning of its life.
MTTF = 1 / failure rate (if constant)

What is Mean Time To Repair (MTTR)?

MTTR-Mean Time To Repair, the average time to correct a failure and return the equipment to a condition where it can perform its intended function: the sum of all repair time incurred during a specified time period (including equipment test time), divided by the number of failures during that period.
MTTR= Total repair time / # of failures
and
MTTR = 1 / repair rate (if constant)
To decrease MTTR means that customer satisfaction increases.

What is SIL?

SIL stands for Safety Integrity Level. A SIL is a quantitative index of the required reliability of a safety-related system as a function of the criticality of the process. The international standard IEC 61508 defines four SIL levels (1 to 4)

IECEx

Can I use my IECEx certificate to place products on the market in Europe?

No, you must comply with the ATEX Directive (94/4/EC). It is likely that a notified body would accept much of the work carried out and reported in the ExTR.

I already have ATEX certification for my Ex equipment. What do I do to comply with IECEx?

As the product has already been tested, most certification bodies will use the ATEX data they have collected to prepare an ExTR.

What if I am in a country that does not have an IEC national committee?

Manufacturers are free to choose any IECEx-accepted certification body for Assessment & Test Reports for their products.

ATEX relative questions

What equipment has to comply with ATEX for use in hazardous areas?

The ATEX directive applies to electrical and non-electrical equipment.

• For a solenoid valve, it is the complete product comprising the coil and the body which must be ATEX-certified.
• For an electro-pneumatic valve with integrated pilot, it is considered similar to a solenoid valve, so the whole product must be ATEX-certified.
• For an electro-pneumatic valve with a separate CNOMO solenoid pilot, 2 certifications are necessary: one for the solenoid operator and one for the pneumatic valve.
• ATEX certification is also necessary for non-electrical equipment such as filters, regulators, lubricators, valves, cylinders, etc, if used in a certified zone.

If my plant/equipment was installed before 1^st July 2003 and is fitted with equipment certified according to the previous method, should I replace them?

For working equipment sold and installed before 1^st July 2003, a documented assessment of the risks of explosion must demonstrate that these risks have been taken into account. In particular:

• For dust-filled atmospheres: the existing working premises must be adapted to comply before 1^st July 2006.
• For gaseous atmospheres: installed equipment which does not comply with directive 94/9/EC must have been assessed by the site manager. Depending on the risk analysis, the manager decides whether or not it is necessary to upgrade it to comply with directive 94/9/EC. Equipment which has received a positive assessment can be maintained in service after 30^th June 2006.

What does the deadline of 1^st July 2006 correspond to?

On that date, all installations must comply with the ATEX directives.

For working equipment sold and installed before 1^st July 2003, a documented assessment of the risks of explosion must demonstrate that these risks have been taken into account. In particular:

• For dust-filled atmospheres: the existing working premises must be adapted to comply before 1^st July 2006.
• For gaseous atmospheres: installed equipment which does not comply with directive 94/9/CE must have been assessed by the site manager. Depending on the risk analysis, the manager decides whether or not it is necessary to upgrade it to comply with directive 94/9/EC. Equipment which has received a positive assessment can be maintained in service after 30^th June 2006.

Can I mount accessories on the ATEX-certified products?

Yes. See our catalogue "Apparatus for potentially explosive atmospheres" which includes all the compatible accessories which have been the subject of risk analysis. For all other accessories, risk analysis must be performed on a case-by-case basis.

Can I assemble ATEX-certified products?

Yes. For example, a pneumatic valve and a CNOMO interface solenoid valve, a cylinder and an electro-pneumatic valve... as long as the following rules are respected:

• Each product involved in the assembly must be ATEX-certified.
• Take into account the least favourable category and temperature class and make sure that they are compatible with the area of use.
• Check the continuity of the earth connection to allow dissipation of static electricity. This continuity must be ensured on all equipment requiring assembly, whatever the area of use.

Traceability of ATEX products:

Traceability of ATEX products is mandatory from their manufacture through to their use. ASCO Numatics archives information such as customer identification, product code, serial number, date of manufacture and order number.

ATEX maintenance

I want to replace non-ATEX equipment certified according to the previous method on an existing installation. What should I do?

We advise you to replace the old products with ATEX-certified equipment.

Can I repair ATEX equipment?

You can buy spare parts kits for ATEX products and carry out maintenance subject to some conditions:

• You must comply with instructions contained in the installation and start-up guide delivered in the spare parts kit.
• You must ensure traceability of the repaired ATEX product.
• The technician performing the repair must have received sufficient training concerning the ATEX directive and the risks of explosion.
• The conformity of the markings must be checked (manufacturer's markings, modification/repair markings).
• You must change the existing ATEX label:
  • either by replacing it with a new label, called a modification/repair label
  • or by adding a specific identification mark (e.g. addition of the letter "R")

What should I do with equipment in stock not installed before 1^st July 2003 and not compliant with the ATEX 94/9/EC directive?

You cannot use these products for installations set up after 1^st July 2003.

For installations in service before 1^st July 2003, a documented assessment of the risks of explosion must demonstrate that these risks have been taken into account. In particular:

• For dust-filled atmospheres: the existing working premises must be adapted to comply before 1^st July 2006.
• For gaseous atmospheres: installed equipment which does not comply with directive 94/9/EC must have been assessed by the site manager. Depending on the risk analysis, the manager decides whether or not it is necessary to upgrade it to comply with directive 94/9/EC. Equipment which has received a positive assessment can be maintained in service. In that case, you can use your equipment in stock to replace any defective equipment if it complies with the former CENELEC regulations.

Is it possible to repair an old non-ATEX product for use in an explosive atmosphere?

Yes, if the equipment installed complies with the previous regulations and the installation does not require adaptation to comply with directives ATEX 94/9/EC and 1999/92/EC.