I’m working on a older building that has a set of fire doors held open by a cotton rope over a pulley to a weight.
If the rope is cut (or, less happily, burned through), the doors will roll down an inclined track and close.
What device might be available to automatically close this style of door in case of alarm activation?
A Rixson 972S magnetic sliding door release might work for you.
Looks pretty good (Though I’d have to build my own manual release button). Thanks.
Magnetic door holders are typically held by power provided by the FACP, when the power drops they release. Whenever the fire alarm activates, or when the fire alarm loses power, it should drop power to these door holders and the door should close. You shouldn’t need a manual release, and if someone wants to shut the door for whatever reason in a non-fire alarm situation, they just have to give it a good yank, it’s only 30-40lbs of holding force usually.
Chris+s is correct about the door holder operation. The 972S is made for heavier doors and is rated at 75 pounds holding force. Might need a really good yank.
If an electrical manual release is still desired, it is quite easy. Since the holder releases the door on power loss, all that is needed is a normally closed momentary switch in series with the holder. Push the button, holder looses power, and the door closes.
This doors are currently set up with a counterweight, so they open and close with a light touch.
It gets “closed” so people can access a storage area behind it, but is “open” the rest of the time.
The magnetic catch would require adjusting the counterweight so the door reliably closes.
Magnetically releasing the counterweight rope would be better in some ways: the door would
close convincingly.
24V Rotary knives to cut the counterweight are presumably not an option 
Thanks for your help.
Unless you don’t want your fingers… lol Just imagine if your right near that thing when it goes off. Bad news.
Ok ok. An electromagnetic release on the rope. Magnet releases, counterweight drops into it’s pocket.
I’m just curious, if the doors were never set up to operate in this way (automatically closing on an alarm activation), why set them up now?
Also, the setups I’ve see utilize a listed fusible link that would melt at 165° and release the door. Never heard of a setup that would require a rope to burn to release unless it’s something before my time! I wonder if someone has removed the link in your case?
Now that could work…