# vacuum pump from air horn compressor



## iss407 (Dec 6, 2007)

I have been thinking about inexpensive options for a vacuum pump. I remember somone talking about taking a small 12V inflator pump and reversing it to pump air out and create a partial vacuum. Those pumps are meant for high-pressure and low volume. What we need in an EV is low pressure and high volume. Then it hit me: a 12 V air horn compressor such as the Wolo 808-C. I need a vacuum reservoir anyway and most people make that out of a PVC tube. What if I put the air horn compressor in the reservoir and vented the output to the atmosphere through a check-valve? Bingo: resevoir and pump in one.

The Wolo 808-C generates about 22-23 PSI, or about 45-in. hg. That is 75-in. absolute starting with 30-in. atmospheric or 2.5 times the input pressure. If I scale that ratio down then the 30-in. atmospheric pressure that becomes the compressors "output" would be 2.5 times the 12-in. absolute pressure inside the reservoir. That is 18-in. of vacuum, plenty enough for the brake booster and any other vacuum accessories on the car.

I haven't tried this yet, but I think it is worth $33 plus shipping to find out. I'd need to build a reservoir anyway, so no extra expense there. What do you think, could this work? Air horn compressors are able to push a fair amount of air, plenty enough for a brake booster I would think. Am I thinking straight?

Thanks.

-- Paul


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## rillip3 (Jun 19, 2009)

iss407 said:


> I have been thinking about inexpensive options for a vacuum pump. I remember somone talking about taking a small 12V inflator pump and reversing it to pump air out and create a partial vacuum. Those pumps are meant for high-pressure and low volume. What we need in an EV is low pressure and high volume. Then it hit me: a 12 V air horn compressor such as the Wolo 808-C. I need a vacuum reservoir anyway and most people make that out of a PVC tube. What if I put the air horn compressor in the reservoir and vented the output to the atmosphere through a check-valve? Bingo: resevoir and pump in one.
> 
> The Wolo 808-C generates about 22-23 PSI, or about 45-in. hg. That is 75-in. absolute starting with 30-in. atmospheric or 2.5 times the input pressure. If I scale that ratio down then the 30-in. atmospheric pressure that becomes the compressors "output" would be 2.5 times the 12-in. absolute pressure inside the reservoir. That is 18-in. of vacuum, plenty enough for the brake booster and any other vacuum accessories on the car.
> 
> ...


No idea about any of that, but 18" should be plenty; from whatI've read, 14" is the minimum and 17" the recommend.


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## Coley (Jul 26, 2007)

This idea was brought up last year by me and was told the compressor would run too hot in the closed chamber.
Since then, a fellow has been advertising just such a setup and says it runs fine.
I am building my own and you sure could also.


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