Control relays - constantly energized

[mshields]

I'm supporting a system that has a constantly energized solenoid valve (controls Liquid CO2). The circuit is fail safe.

They've asked that we add a relay such that a BMS will get a signal in the event of one of the EPO's (N.C.) opens the circuit and or a power failure. My concern is that in order to do this, unless they can find a solenoid with aux contacts, I'll need to put in a relay that is also constantly energized. I believe having a relay constantly energized like this is to be avoided; that the coil will burn out.

a) do they make relays suitable for constant energization and/or b) is there a better way to do this?

Thanks

 

[ptonsparky]

Look at the problem as it is. They want it to fail safe. Power failure=Off. Coil failure=Off

The control circuits we have are constantly On. Power failure and pressing the Estop or Control Stop is all that shuts them down.

Done all the time.

 

[richwaskowitz]

I am not sure where you are getting your concern from. I have seen solenoids (in the auto assembly industry) with millions of cycles on them sitting next to the same kind of solenoid which has been energized practically continuously for many, many years with no failures.

When you ask about a better way, are you referring to a better way to monitor CO2 flow (like a flow or pressure switch) or a better way to keep CO2 flowing without keeping a solenoid energized?

 

[zbang]

a) do they make relays suitable for constant energization and/or b) is there a better way to do this?

a) sure, most of them.
b) you could use a SSR instead of a mechanical relay.

 

[mshields]

cool

cool

thanks

 

[Ingenieur]

many relays are rated continuous duty cycle
http://www.mouser.com/catalog/english/101/apac/1778.pdf

Continuous duty cycle

make sure you pick one that is

 

[petersonra]

most industrial relays are going to be fine if continuously energized.

call your local electrical house and have them get you one.

it will probably outlast you.

you can probably get one for less than what the time is worth that you spent posting this and reading the replies.

 

[Phil Corso]

Mike,

This question is in the domain of SIS or "Safety-Instrumented-Systems" Years ago, they were referred to as, ESD or "Emergency Shutdown Systems!"

Fail-safe is no longer used! Today, "DTT" or "ETT", meaning De-energize-To-Trip, or Energize-to-Trip, is the criterion, used!

If the facility or circuit for which "Fail-Safe" is requested, has boilers other combustion-related hazards, "DTT" is required, by law!

Be very careful! You are entering the world of Liability! I know it well, having been sued twice, once by a Utility, the other an HPI co.! And, even though I was vindicated in both situations, I lost a huge $$!

Paraphrasing a well known idiom, "If you can't "Define" You Must Decline"!

Regards, Phil Corso

 

[Ingenieur]

Mike,

This question is in the domain of SIS or "Safety-Instrumented-Systems" Years ago, they were referred to as, ESD or "Emergency Shutdown Systems!"

Fail-safe is no longer used! Today, "DTT" or "ETT", meaning De-energize-To-Trip, or Energize-to-Trip, is the criterion, used!

If the facility or circuit for which "Fail-Safe" is requested, has boilers other combustion-related hazards, "DTT" is required, by law!

Be very careful! You are entering the world of Liability! I know it well, having been sued twice, once by a Utility, the other an HPI co.! And, even though I as was vindicated in both situations, I lost a hu$$!

Paraphrasing a well known idiom, "If its not "Defined" You Must Decline"!

Regards, Phil Corso

SIL!!!!!

(my you use a lot of !!!! marks!!!!)

 

[Phil Corso]

SIL!!!!! (my you use a lot of !!!! marks!!!!)

Wait 'til you're as old as I am!:lol:

Phil

 

[Ingenieur]

Wait 'til you're as old as I am!:lol:

Phil

I am fast approaching, no doubt
getting old is better than the alternative lol

 

[Jraef]

I would do it with a little current sending relay. Current flowing, circuit is good. No current, something is wrong. That covers more than just the relay, it covers wire breaks too.
http://www.nktechnologies.com/current-sensing-switches/as1-dodc-current-sensing-switch/

 

[Ingenieur]

I would do it with a little current sending relay. Current flowing, circuit is good. No current, something is wrong. That covers more than just the relay, it covers wire breaks too.
http://www.nktechnologies.com/current-sensing-switches/as1-dodc-current-sensing-switch/

wouldn't a remote normally energized relay in parallel with the solenoid valve holding n/o contacts closed (de-energize on loss of voltage, broken wire, etc., so contacts open)
the contacts of which go to the monitoring system or holding a control panel relay in?

it's not supervised like a ckt with eol resistor but imo (with the correct relay) meets a SIL 3 level

I might look at monitoring the actual valve position or line pressure

 

[Jraef]

The OP never mentioned SIL. He stated this was for a BMS (Building Management System, aka HVAC). I doubt there is an official safety regulation involved in notifying the BMS, it's probably more of a convenience thing.