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Topic Title: Ex Solenoid valve through I.S barrier
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Created On: 21 July 2010 12:02 PM
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 21 July 2010 12:02 PM
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Avatar for anthonybates1980                                  .
anthonybates1980

Posts: 20
Joined: 25 July 2008

Hello,

I have been asked by a mechanical colleague why a solenoid valve on an oil flush system is not working. On inspection I discovered that the solenoid coil is 9w and is fed through a hazardous area barrier which limits the current to 65mA (1.56 watt). Obviously the 9w coil takes 375mA so could never have worked (although my colleague is adament it did!). Does anybody know of a 2port 2 way solenoid valve which can be driven through the barrier or of a barrier which will drive the 9w coil? Coil is operating on 24VDC.
Or have I missed something obvious?!!!

Many thanks

Tony
 21 July 2010 10:00 PM
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ArthurHall

Posts: 735
Joined: 25 July 2008

The whole point of the IS barrier is to limit energy on the hazard side so you will never drive that valve through a barrier. If the valve is Ex do you need a barrier? My only other thought is to use air to drive the valve.
 22 July 2010 09:30 AM
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Avatar for anthonybates1980                                  .
anthonybates1980

Posts: 20
Joined: 25 July 2008

Arthur, thanks for the reply.
I am relatively new to hazardous area installations, but I asked the same question, the solenoid valve is Ex so why does the current need limiting through a barrier? It seems a double safety feature! I also questioned why producers would manufacture an ex solenoid at a wattage above the spark limit if it needed protecting through a barrier? Unfortunately the design engineers involved in the original installation have all left. So my best sources of info are engineers like yourself on the IET forum.
Again thanks for the reply.

Tony
 23 July 2010 08:34 AM
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StewartTaylor

Posts: 99
Joined: 18 January 2003

Tony,

If your solenoid valve is Ex certified to ATEX and has a 9W coil then it must be Ex 'd' (explosionproof), Ex 'm' (encapsulated) or similar - check out BS EN 60079 for more details of protection methods. What you refer to as a hazardous area barrier is only required for protection by Intrinsic Safety (Ex 'i'), which depends on limiting the energy in the circuit to a value too small to cause a spark that can ignite the potential explosive atmosphere.

The only conclusion is that if it ever worked then the I.S. barrier is a new introduction, or maybe the valve had an I.S. certified coil and it's been changed to one with some other protection type.

If your plant's protection method is I.S. then you'll need to find a valve with an I.S. coil or an I.S. coil for your valve - not too hard. Try Asco, Maxseal, Lucifer, for example (no recommendations there, these are just the ones we use kind of every day).

If the coil is Ex 'd' or one of the other types you don't neede the barrier at all, btu if the plant is generally I.S. you should stay in line, particularly because it's safe to open I.S. equipment housings with the power on but it's unsafe with most other methods.

Also, if you're using an I.S. barrier, make sure it's either a galvanic (transformer isolated) barrier or, if it's a zener barrier, that it has a good quality earth direct to the plant earth reference. connection to the plant safetry earth is not good enough because electrical regulations allow too much voltage build-up on the earth connection under fault conditions.


-------------------------
Reality is that which, when you stop believing in it, doesn't go away.
 26 July 2010 10:21 AM
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geoffreyspark

Posts: 1
Joined: 26 July 2010

Some other things to consider... from your discription I would make the assumption that the solenoid would not operate with a 9 watt coil (as was your initial opinion).
If you can trend the point you will be able to find out the last time that the valve operated. Then talk to the people/maintenace supervisor to assertain if any breakdown maintenance or routine maintenance was undertaken as this could explain why there is a 9 watt coil installed or new barrier fitted.
please let us know the result of what you find.
 27 July 2010 01:31 PM
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chartassuk

Posts: 50
Joined: 25 July 2008

Hello anthony,

If this installation is within a Hazardous Area then what is the Zone classification, gas group and temperature class required for equipment?

To simply change the solenoid will require:

a) for an Ex'i' system:

Verification that selected components meet or exceed above criteria

ATEX certificates for all components in the circuit (noting if there is a X suffix which denotes special conditions for use)

Recalculation of Descriptive System Document (DSD) as per BSEN60079-25

Redrafting of component block diagram as per BSEN60079-25


b) for an Ex 'd', 'e', 'm' or other concept of protection:

Same as for EX'i' with the exception of no DSD required


c) work carried out by a (CompEx) Hazardous Area competent person

d) inspected and verified by a Hazardous Area qualified supervisor and recorded on a BSEN60079-17 installation certificate.
 01 August 2010 10:18 PM
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HTDearden

Posts: 90
Joined: 26 February 2002

chartassuk lists considerations relating to the change of the solenoid - fair enough. But the list maybe looks a bit scary - just to reassure:

Yes the components must meet the area zone/gas group/temp class. You do not have to hold certificates for all components - you need to be confident the equipment is suitably certified. You must comply with any special conditions if there is an X suffix.

Descriptive document just needs to identify the equipment and the associated parameters. Cable typically only a potential concern if >500m. Should confirm field equipment parameters consistent with barrier parameters (Vi, Vo, Ii, Io, etc .) Nothing difficult here.

Work should of course be carried out by competent people - that does not mean they have to be CompEx trained. Installation requirements for Ex i are not difficult. CompEx is one way of gaining a degree of confidence in competence - but it is not the only way.

Work should of course be inspected for QA, but again not that profound really. You do not have to use BS EN 60079 certificate.

As always what it comes down to is using competent people and taking all reasonable steps to make safe.

Note that if a 28V 300Ohm zener barrier used say, max power transfer would occur with 300 Ohm coil, but available voltage would only be ~12V, NOT nominal 24V. Volt drop in barrier circuit limits available voltage.

-------------------------
HTDearden CEng
Consulting Engineer
www.tdsl.org.uk
 13 August 2010 11:25 AM
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chartassuk

Posts: 50
Joined: 25 July 2008

Valid points HT, but I tend to be zealous on documentation and proof because in many facilities I have audited management of change control is very poor. This isn't second or third tier operations either.
 11 October 2011 04:13 PM
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Avatar for anthonybates1980                                  .
anthonybates1980

Posts: 20
Joined: 25 July 2008

Thanks to you all for responses. Using your comments and my increase in knowledge through experience and training I am fairly comfortable now when designing/troubleshooting ex installations.

many thanks

Tony

Geoffrey this post was sometime ago, but I came to the conclusion that the solenoid could never have worked. I would assume it was fitted in error as part of maintenance work.
 12 October 2011 08:35 AM
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oneye

Posts: 158
Joined: 25 February 2008

IMO you should don the hat of an E,C&I safety officer and note the situation you have found as a possible reportable offence.
Unless you are absolutely sure you are intending to place the 'kit' back into the same safety category as before, you would need to (self-certify) the change. At this point you would advise the Technical Director who would soon let you know if you are going down the wrong route.

You have not mentioned cabling....
was the cabling to the solenoid recently and completely rewired from the barrier.
If not what colour is the sheath. If mid-blue colour does it exit the barrier outwards in blue trunking and is it segregated from other coloured cables (including black). Existing blue cable would suggest I.S., whereas any other colour /black would suggest Ex'd.

You haven't convinced me you know which it was. You need to put it back as it was; and make a record of how and why for future reference.
 12 October 2011 10:16 AM
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Avatar for anthonybates1980                                  .
anthonybates1980

Posts: 20
Joined: 25 July 2008

oneeye, just to clarify this was posted some time ago. As I remember and have stated, the solenoid was protected by a barrier thereby making it IS and as a result in blue cabling. I seem to remember that after some investigation the conclusion was that at some point before the solenoid had failed somebody had replaced it with an Ex d component. What puzzled me at the time was that the mechanincal department were adament that the valve had been working. This would obviously have been impossible.

Due to the task the solenoid valve was performing it is quite reasonable to conclude that it would not have been detected as failed.

thanks for your post

Tony
 13 October 2011 08:42 AM
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oneye

Posts: 158
Joined: 25 February 2008

Tony,

It matters not that this is an old thread.
If persons unkown have unwittingly or otherwise have changed the safety characteristics of an existing and presumably once working system then they may have breached the related ATEX certification.

Any components should .be replaced with the same or identically specified as original. Had that occoured you would not need to raise the point.

As raised in the 1st post, an I.S circuit solenoid untilises far less energy than an Ex'd and thus will have a completely different valve and pilot arrangment.
 14 October 2011 03:22 PM
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Avatar for anthonybates1980                                  .
anthonybates1980

Posts: 20
Joined: 25 July 2008

Oneeye, thanks again for response I was stating it was an old post purely because my memory is bl***y awful so some of the details are not as fresh in my mind as they originally were. Anyway completly agree with your comments and the incident was satisfactorily resolved shortly after the original post.

Again thanks

Tony
 23 October 2011 05:33 PM
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Avatar for MAXMIRA.
MAXMIRA

Posts: 78
Joined: 25 January 2011

Anthony, can you tell us which solenoid you used to replace it?
 24 October 2011 01:55 PM
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Avatar for anthonybates1980                                  .
anthonybates1980

Posts: 20
Joined: 25 July 2008

Maxmira,

Going back through my old notes I believe it was a Parker 321H1590. Solenoid 24VDC 0.4W.

Kindest regards

Tony
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