vacuum valves
alnajjar
Posts: 12
I am designing an exhibit with to demonstrate that the transmission of sound depends on the presence of a medium.· In this case a vacuum pump sucks the air out of a bell jar and reduce the amount of sound from a siren inside.·
I am using a BS2 to control the pump with a solid state relay but I need help with two things:
1.· need to controll a valve to let air back into the·bell jar or close to create vacuum inside it.
2.· i need to measure the db inside and outside the bell jar.· this does not have have to be absolute measurement and should only indicate relative values.· I remember seing a post about using a mic to measure sound intensity· but it would be great to have other's experience.
many thanks,
Al Najjar
I am using a BS2 to control the pump with a solid state relay but I need help with two things:
1.· need to controll a valve to let air back into the·bell jar or close to create vacuum inside it.
2.· i need to measure the db inside and outside the bell jar.· this does not have have to be absolute measurement and should only indicate relative values.· I remember seing a post about using a mic to measure sound intensity· but it would be great to have other's experience.
many thanks,
Al Najjar
Comments
Here is a link to a site for air valves
http://www.clippard.com/store/byo_electronic/byo_mouse_valves.asp
This is typical of solenoid actuated air valves.
You want a 3-way valve. This means that your vacuum pump will pump through the valve when it is activated, and the vacuum will be held so long as the valve is activated. When the valve is deactivated, air will bleed through the valve back into the bell jar until equalized. I would buy a small needle valve at any local hardware store and screw it into the exhaust port of the valve. This will allow you to adjust the rate of bleed back into the bell jar.
When you shop for a valve, be aware of the negative pressure rating for the valve. Make sure yours will support the vacuum you need. Many valves are designed for positive pressure only and will leak under negative pressure. The valve referenced in the link will handle 28 inches of mercury of negative pressure.
DC valves typically require supply voltages if 6, 12 and 24 volts. You must use a suitably sized transistor or relay to switch the valve. Again, the coils for the above referenced valve: 6 volts - 54 ohms, 12 volts - 218 ohms and 24 volts - 864 ohms.
Good luck,
RTurley
Post Edited (RTurley) : 1/29/2005 3:14:15 PM GMT
Thanks for the info!
Shawn Lowe
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Shawn Lowe
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