Vacuum switch, where/how ? - RC Groups
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Jan 16, 2006, 02:39 PM
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Vacuum switch, where/how ?


I've gotten my hands on a very nice vacuum pump with a 3-phase motor. It's a *bit* overkill but I got it for free, so...

It's one of those heavy duty rotary vane pumps, which is nice. Problem 1) is that it doesn't come with a vacuum tank and 2) that it doesn't have a presure regulated on/off switch. A solution to 1) is dead-simple, but problem 2) is a bit more intricate.

I've scanned the web for a few hours but cannot find anything suitable and obvious that would work at a moderate price. The closest I've gotten so far is a 1-phase (240V) switch directly actuated by the vacuum pressure at a semi-high US$70 (roughly). It is a bit on the high side though since it is not enough as a complete solution.

Does anyone have experience with solving this problem ? All input is appreciated.

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Jan 16, 2006, 05:37 PM
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CST sells vaccuum switches, they are not rated for that pump. Solution is to use the switch to drive a relay or solid state switch tha can handle the current used by the pump. That way the switch would only handle the current of the relay.
Jan 16, 2006, 06:21 PM
SEFF Contest Director
rcjunkie's Avatar
The CST switch will work like jcyr1 said with the relay and will cost about $35-40.

Also to take care of the vacuum tank issue, I used an empty Helium tank on my setup and drilled a hole thru the case and screwed in a fitting with RTV around it to make sure it was sealed. It works great and cheap. Some people use a section of 4-6" PVC pipe with endcaps on it and make a vacuum tank out of it.

Ernie Schlumberger
Jan 17, 2006, 05:41 AM
chetosmachine's Avatar
i'm working on my pump and have a pair of questions:
-i bought a vacuum switch which i want to operate through a relay. Does anyone have a scheme of the connection?
-i have an empty gas can. It's from a torch, and is around 15" tall * 4" diameter. Does it have the right size or is it small?
thank you,
Jan 21, 2006, 12:42 AM
I looked all over when I was trying to find a vacuum switch. Check out the vacuum switches sold by Digi-Key. The one I use (part # 384-1009-ND) is rated at 25A and can be set from 6" Hg to 24" Hg (81" to 330" H2O). You shouldn't have to use a relay with the switch and the Best thing about it - it cost $16.24 + $5.00 S&H.

Look at the bottom of the page for the World Magnetics Pressure (& vacuum) switches.

Digi-Key home page is

When you choose a vacuum tank, remember that you will want the most capacity that you can reasonably get away with. The reason is you are only working from 0.0 to 1.0 atmosphere (or 0.0 to 14.7 psi), unlike the normal range of compressors which operate over several times atmospheric pressure (100 psi is almost 7 atmospheres). I set up my system with a 6' length of 4" PVC pipe, which works OK but if you get a leaker vacuum bag, the cycle time on the vacuum pump is still noticeably short.

Good Luck

Last edited by fishinrflyin; Jan 21, 2006 at 01:18 AM.
Jan 27, 2006, 05:21 PM
Registered User
I have not build my yet. But I like to use the vacuum part from a car engine.
The vacuum bell that adjust the timing of the spark.

Just add a spring and a switch.

Jan 31, 2006, 01:13 AM
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G'day, have you guys sussed out the diagram on the ACP website. I was able to follow this for connection of the relay switch and associated wiring.

Also they have Vac switches for $39US. Works pretty well in my set up.

Jan 31, 2006, 10:45 AM
Tarzanstyle English Sorry
AgoMago's Avatar

Home made vac switch

I solve the problem in that way!
And only 2 $ !!!!!!
Jan 31, 2006, 12:42 PM
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pinolefm1's Avatar
Originally Posted by AgoMago
I solve the problem in that way!
And only 2 $ !!!!!!
Very ingenious...Rube Goldberg would've been proud

Feb 03, 2006, 01:52 AM
Registered User

lid Flex ?

The vacuum causes the lid to flex enough to trigger the microswitch ?


Originally Posted by AgoMago
I solve the problem in that way!
And only 2 $ !!!!!!
Feb 04, 2006, 05:35 AM
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HELModels's Avatar
That is too efficient to be Rube Goldberg. Rube was forced to study engineering and chose to be an artist.

It must switch off when the vacuum is highest, so the switch would lose contact. That would require the jar to be glued to the base, for the flexing of the lid to control the contact. Evacuating the jar causes the lid to want to cave in, i.e., flex down switch off. The spring provides tension to delay the flexing down and encourage the flexing up? The tension is adjustable, if you look closely. ??????? Choose the wrong spring and it wont work?

Looking at the arrangement of the tubing, is critical to understanding this rig.
I imagine a venturi effect putting pressure on the jar, causing the jar to lose contact with the switch, but when? When the vacuum is building or after?
Maybe Tarzanenglish can explain.

Unlike Rube, I studied Art first and can only admire engineering.
Last edited by ElectroStorch; Feb 04, 2006 at 06:23 AM.
Feb 04, 2006, 10:32 PM
Registered User
I posted this quite a while ago but here is where I found a place to get vac switches
not sure if they have any 3 phase or not but you might check them out.

this is a repost of my response to another question about vac set ups....

I found a place to get the same vac switch sold at one of the composites stores for less than half price.
look in their subminature vac switch section, the one I like is
V-5100 28 FM B85 25a
it is variable from 3-28 inches of vac and can be bought at 15 amps or 25 amps
(thats the 25a number at the end).
Air logic only sells wholesale, but if you call them they will tell you where the nearest
dealer is.

good luck

Feb 05, 2006, 01:56 AM
Registered User
HELModels's Avatar
Originally Posted by AgoMago
I solve the problem in that way!
And only 2 $ !!!!!!
Is the glass jar firmly attached to the wooden base? I can see that you sealed the connection to the lid, so eVacuating the jar must be the goal.
Is it the flexing of the lid that controls contact?

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