Paint Booth Interlock

[rogue6144]

I have a customer that wants to interlock the ventilation on an open faced paint booth to the spray equiptment. Monitoring the air flow in the exhaust duct seems like the way to do it.Since the inside of the duct is class 1 div 1, Would a general purpose air sensing switch be ok if it was mounted outside of the hazardous area?The sample tubes would be long enough to do this. Also, there is a slot in the duct for the belt driving the fan to pass through. The motor is general purpose, and within 3 ft of this slot.Wouldn't this be a violation? Thanks for any input.

 

[chris kennedy]

Welcome to the Forum. Why not use a solenoid on the spray compressor to hood contactor?

 

[mcclary's electrical]

To me, an air flow monitor it a paint booth is setting yourself up for failure. Why not come off aux. contacts of blower motor. Use this to interlock a solenoid valve that won't flow air unless it has an input (from contactor)

 

[rogue6144]

Thanks for the quick responses! I thought about interlocking through the contactor or a current sensing switch, but if the motor or belt belt failed, the contactor could still be closed, thus allowing the solenoid to operate.

 

[76teach]

The use of an air proving switch, wich is a diferential prewsure switch with air sampling tube into the exhaust duct to open an electric air solendoid in the line to the spray gun only when air movement is proven is good proceedure. You may already be describing the DP switch in your mentioning of tube.

 

[mcclary's electrical]

Photohelics and magnehelics do not like dirty air!
i think it would be a mistake to use one in this application.about the other idea, Yes,,,if the belt failed you could not move air and still spray, but that's a small price to pay for reliability. I still think it will work better than a paint filled photohelic.

 

[don_resqcapt19]

You could use a speed switch on the fan shaft to get around the issue of a broken belt, or you could look at a "sail" switch in the exhaust. The sail switch will work better than a sensing tube in the exhaust air flow, but it too will get gummed up with paint to the point it will no longer function at some point

 

[mcclary's electrical]

Good point, Don. I think that would make it fool proof. Zero speed proximity switch of blower shaft. Bingo

 

[rogue6144]

Thanks again for the input. I think I've narrowed it down to a current sensing switch or proximity sensor.

 

[wireguru]

expensive, but this allows you to set a minimum shaft speed threshold, and is a proximity sensor so theres nothing to get gummed up with paint.

http://store.controlconceptsusa.com/page6.html

 

[CWillcox]

Moniter Fan amps

Moniter Fan amps

An option that we use on critical fans is a device from Load Controls

http://www.loadcontrols.com/products/products.html

The challenge is the inital set-up but once it is done, very nice unit.