Intrinsically safe solenoid valves 1

[garfio]

We specified solenoid valves for our ON/off valves to work with 120 VAC. Some of these solenoid valves must operate in a classified area and require to be intrinsically safe. The vendor says that is impossible to obtain intrinsically safe solenoid valves operating at 120 VAC. Any information about it?

 

[waross]

I agree with your vendor. Intrinsically safe basically means incapable of igniting the flamable substance the device is rated for. I think that you have specified a device that does not and can not exist. Try going with explosion proof solenoid valves and wiring.
respectfully

 

[ScottyUK]

waross is right: an I.S. device typically draws only a few mW from the supply. The supply, which is usually through a barrier or galvanic isolator, is inherently incapable of delivering more than a fraction of the energy required to cause ignition, hence it is 'intrinsically safe'. The maximum amount of energy depends on the type of gas, but is never high enough to operate a normal solenoid valve. I have used hydraulic servo valves in I.S. circuits, but these draw tiny currents at limited voltages.

If you are designing or specifying equipment for a hazardous area then get help from someone who knows what they are doing. The questions you are asking demonstrate that you don't have sufficient knowledge to do this design to a competent level. There are the obvious safety implications of getting it wrong and under the European ATEX legislation both you personally and your employer are liable for the installation design. I am unsure what applies in the rest of the world.


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Sometimes I only open my mouth to swap feet...

 

[garfio]

Thanks for your response. I believe I didn't give the whole information required. The on/off valves are pneumatically actuated. The solenoids just control the air flow to the actuator. I understand the principles behind the intrinsically safe design. In our installation, we have intrinsically safe instruments operating at 120 VAC. I know that a solenoid could draw more current than an electronic instrument. In case of solenoid valves, I've seen them operating usually under 30V. I just needed a confirmation that they really don't (or can't) exist. It might be that they are rare/expensive but still possible to get.

Is it positive that these valves don't exist even for the small sizes?

 

[danw2]

3 and 4 way IS solenoid valves from ASCO

http://www.lesman.com/unleashd/catalog/valves/valves_isseries.html

 

[danw2]

ASXO solenoids are 24Vdc only.

You will not find 120Vac IS valves. 120Vac will only come in EXP explosion proof style.

 

[pooslinger]

Can the electric solinoids be positioned remotly or out of the area? I am not sure how long an air line can be before the performance of the actuator becomes degraded. I have replaced OEM solenoids on actuators with ASCO three ways. The ASCO three ways must be mounted on the wall where the air is fed with copper tube to the actuator. The OEM was mounted directly onto the actuator.

 

[ScottyUK]

danw2 -

They're interesting - they use a capacitor to store enough charge for pull-in, so they're a little sluggish to respond according to ther datsheet, but they might be very useful in certain designs. Definitely a product to bear in mind for the future. If only they were available with an ATEX certification...


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Wow those fly in the face of logic!!
I design I.S. equipment. Capacitors are one of the great, 'must avoid', evils because obviously they can take some dribble thru a barrier and pile up a huge amount of ignition energy.

Asco has cleverly gotten around it by making those valves actually EXP valves driven via I.S. sources. This also explains how they can get around the REALLY serious energy associated with an operating solenoid. They house the CAP and the Solenoid in an EXP housing and double diode protect the supply line from ever seeing any of the cap or inductor energy.

I like it!

It will of course have speed issues.

Normally people do it the standard way of running whatever dang solenoid/valve they want outside the hazardous area and just run air into the area. Most applications can handle the typically small delays incurred.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[davsy]

lavals

In our installation, we have intrinsically safe instruments operating at 120 VAC.

What type of instruments do you have that are Intrinsically Safe and operate at 120VAC. What Barriers do you use and what Class/ Division (or zone) are they operating in.

I am interested as I had never seen anything I.S. with such a high voltage before.

 

[ScottyUK]

I guess Keith means 'Explosion Proof' when he says EXP? In IEC-land, Ex'P' is a form of protection which employs a positive pressure within an enclosure to prevent ingress of the flammable material. Usually found in larger cabinets and the power is interlocked to a differential pressure switch to trip if pressurisation is lost. I will have to watch out for that abbreviation in future!


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Yeah me too it looks like.. Around here EXP is the 'heavy iron'.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Ah, in our part of the world that equipment is known as Ex'D'. We know it as 'flameproof' rather than 'explosion proof' too.


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

You people and your Logical Terminology! Sheesh! You take all those opportunities for definitional arguments out of your work! Tisk tisk.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

ScottyUK: >If only they were available with an ATEX certification...

Apparently, the ATEX version is handled by ASCO's Joucomatic division.
The IS valves are known as ISSC, series V1050-2

Go to

http://www.ascojoucomatic.com/wbs/w3b.exe/_en/483/497

scroll down more than half way to find the link to the spec sheets for the ATEX I/S offerings:

EEx i (intrinsically safe), ATEX

Dan

 

[ScottyUK]

Thanks Dan. Star for you.


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Sometimes I only open my mouth to swap feet...