About using a low fog machine

[kuming]

Hi,long time no see in here, I already graduated from my school and still keep working in a theatre.

 

This time I have a question about the low fog machine. In my theatre, the hirer is using a low fog machine(CO2) to make the dry ice effect.

However, the container of CO2 release the pressure and make a very loud "Bull" sound suddenly in the show time. That is horrible.

The contractor of this effect company already want to avoid this situation, their technician already release the gas between 300-350 pa.

I know the pressure in the container change because of the temperature. But it seems the pressure is keep on raising and never drop down if you do not open the valve for releasing the gas. Why does it happen this situation? I don't understand, is that have any other issue to make the pressure of the container keep on raising? And the technician told me the one of valves on the CO2 container can also control to raise up the pressure inside the container.

Does anyone know the construction about CO2 container and the valves??

Um......What can I do or the hirer do can avoid this situation happen?

 

BTW, I would like to ask what is the differences of the effect between using the CO2 or the N2.

 

Hope any brothers can help me to answer the questions.

 

Best Regards,

J. Ku

[Kevne]

Turning down the valve on the gas bottle won't work. All that'll do is reduce the amount of CO2 in the mixing chamber. The smoke then won't cool sufficiently and will rise much quicker.

 

The only thing you can do is put the machine somewhere farther from the stage and use ducting to convey the smoke to where you want it. Otherwise there are other machines that use a refrigeration unit to cool the smoke rather than CO2. They aren't as good but they are much, much quieter. The other alternative is good old fashioned dry ice.

 

I'm not sure what you are asking with regards to pressure but it suffices to say that reducing the pressure won't solve your problem.

 

With regards to Carbon Dioxide vs Nitrogen, I can't say I've never used Nitrogen. However, theoretically it has a much lower boiling point than CO2 so it would be more efficient at cooling the smoke? I'm sure someone on here knows for sure. I do know Nitrogen is more expensive than CO2!

[scjb]

I think the OP is referring to the safety vent on a low-pressure CO2 dewar, rather than the high-pressure bottles? It can have an annoying tendency to vent at the the most unfortunate moments! Used to scare the crap out of me when I was working late in the workshop!

 

Assuming your setup is installed correctly (Dewar Basics), to be honest I'm not sure there's a lot else you can do apart from move the machine and dewar further away and duct the lowsmoke, or try and acoustically baffle the dewar in some way?

[Kevne]

I think the OP is referring to the safety vent on a low-pressure CO2 dewar,

 

That makes sense!

 

Whatever type of CO2 low smoker you use, its going to be noisy. Either way, the best solution really is moving the unit and ducting the smoke to the stage as suggested.