Film-Tech Forum ARCHIVE: Air flow indicator for projector exhaust

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Posted by Frank Cox (Member # 6258) on 05-30-2017, 03:04 PM:

I would like to install a flow indicator in the projector exhaust ducting to assure myself on an ongoing basis that the air is moving when I switch the exhaust fan on and the outside vent hasn't frozen shut overnight or something equally exciting.

I'm thinking that something like a vane switch and a sliding dot on the outside of the duct would work, and it wouldn't even require power.

Does anyone know where to get such a thing? Or does anyone have a better idea?

Posted by Steve Guttag (Member # 268) on 05-30-2017, 03:17 PM:

I've seen homemade indicators on the real cheap and they work. Take a piece of solid wire or coat-hanger. drill holes in the duct and stick it through (the holes need to be just large enough to allow it to turn without binding). Take some aluminum tape and make a "flag" out of it and tape that to the middle. Bend the ends of the wire/coat hanger in the same direction. If the exhaust is off, it will naturally rotate down somewhat. If the exhaust is on, it will rotate so it points up.

Posted by Leo Enticknap (Member # 534) on 05-30-2017, 03:17 PM:

Barcos have a temperature sensor built in to the top of the lamphouse: with no external air extraction from the top, the temperature will soon rise into orange tail light territory, indicating that something is wrong.

The extract fans in our booths create a low-pitched hum, the presence or absence of which tells me that they're working or not. Still, I agree - a device that you can simply attach to the duct and which gives you an immediate, at-a-glance indication as to whether the fan is working OK would be a very useful booth accessory.

A couple of years ago, I had a co-worker complain that the booth was getting very hot for no apparent reason. It had been a couple of weeks since I was last at that site. When I got there, I discovered that the roof extract fan for one of the two film projectors had failed (motor shaft had seized). What tipped me off was the horrible flicker when I struck the lamp - shouldn't have been happening with a bulb that had only done 300 hours or so. When I opened up the lamphouse, I saw that the bulb was cooked 'n fooked. From there it was a process of elimination until the bad fan was identified as the culprit. But this guy had been running movies in there for two weeks and not noticed ... sigh.

Posted by Arnold Chase (Member # 7988) on 05-31-2017, 01:52 AM:

I think what you are looking for is a simple flow meter or flow indicator. The indicator will give you a quick go/no-go, while the meters will let you see creeping exhaust system degradation long before things go critical. A cheap indicator that might work for you is:

HVAC companies as well as Grainger sell these.

Posted by Steve Guttag (Member # 268) on 05-31-2017, 06:25 AM:

Remember, anything that would go in the exhaust within sight of the lamp's light has to be good with UV light.

Posted by Arnold Chase (Member # 7988) on 05-31-2017, 02:05 PM:

Other than a very short piece of plastic tubing that is slightly pushed into the duct to be sensed, everything else is outside the duct and UV radiation. In thinking about this further, a far better approach would be just to get an external airflow switch that can sense Positive, Negative, or Differential Air Pressure. I've used these for numerous projects, and all it takes is a small hole to be drilled into the duct to be sampled, and two sheet metal screws to hold the switch to the outside of the duct. The switch is rated for 300 volts (but low current) so it's ideal to activate alarms, etc. Given today's empty projection booths, all the projectors in the house could be easily monitored for partial or total extraction fan failure.

Posted by Mark Gulbrandsen (Member # 72) on 05-31-2017, 02:29 PM:

NEC also uses a temperature sensor system in case of loss of air flow. If it detects an overheat condition it extinguishes the lamp before damage can occur... It actually takes a reboot of the projector to clear this error.

Mark

Posted by Monte L Fullmer (Member # 2797) on 05-31-2017, 04:20 PM:

If you got flex duct, give the duct a light squeeze. You'll feel the air movement through the duct.

Posted by George Germisashvili (Member # 6597) on 06-14-2017, 12:14 AM:

2in1 solution http://www.extech.com/category/?id=14869

Homemade power adapter can be used instead of battery fo 24/7 operating time.

Once we had trouble with NEC 3200S -poor air flow, so NEC did not alarm or do something, just switch off lamp during show, when opened see very black glass on lamp - overheating, lamp become damaged, no strike. It was 5 years ago, and it was some mistake from NEC- regarding recommendations of air flow (it was about 450 CFM after they changed to 565CFM)

Sometime it is good to check manually airflow by cheap meters or smart phone addon

https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Ddigital-text&field-keywords=airflow+meter