Supercharger Abuse Question

[slomove]

I am wondering to buy a cheap used Supercharger from Craigslist and drive it with a 2 hp electric motor as a high power vacuum pump. Vacuum pumps in this power range are normally quite expensive.

I am pretty sure this will work theoretically but I never had a supercharger (Roots Blower) in my hand and don't know what practical obstacles there are, e.g. How that thing is lubricated or what leakage to expect. I am looking to get maybe 75% vacuum (20-25").

Any opinion if that could work? Or just a stupid idea?

[Doug Liedblad]

Magnus is the expert on superchargers but I don't think 2 HP will be enough power to get what you want.

Why do you need the high power vacuum?

[slomove]

Hold-down table for my cnc machine (for sheet material). A wimpy pump will struggle with unavoidable leakage.

The 2 hp motor is a guess. I need to look at some pressure/volume/rpm charts for typical blowers to see if it might work. But I am in Germany right now with only an iPad and a shaky Internet connection.

[Doug Liedblad]

I've seen vacuum chucks in use and they don't need a lot of power. I'd look on Ebay for a vacuum pump. If you don't have a leak it will hold it very well.

[slomove]

I have an 1/3 hp piston vac pump. That is good enough for a vacuum chuck on my wood lathe with a good seal but not for large sheet good that may not be flat and even porous. I have seen professional Cnc clamping vacuum equipment with over 15 hp 380V electrical power. But that is typically for 8' x 4' tables or larger. My machine is a bit smaller and I have anyway only 240V. There is a blower for sale (unknown Ford model) in Azusa for $75 and maybe I just go and play with it.

[Doug Liedblad]

What about just using a large shop vacuum?

[magnusfeuer]

Ehm.

My experience with superchargers are in a purely automotive application. That said, it should work quite nicely as a vacuum . You should also be able to modify a regular air compressor, let it vent to the atmosphere and use the inlet as a source of vacuum. Or, if you want to go fancy, run it backwards and use the tank as a vacuum reservoir.

/Magnus F.

[Doug Liedblad]

Gert

A vacuum reservoir is a good idea. Brother Tom mentioned that when I asked him how they do the vacuum table at the woodworking shop.

[magnusfeuer]

Just don't overdo it with the vacuum.

[slomove]

Ehm.

My experience with superchargers are in a purely automotive application. That said, it should work quite nicely as a vacuum . You should also be able to modify a regular air compressor, let it vent to the atmosphere and use the inlet as a source of vacuum. Or, if you want to go fancy, run it backwards and use the tank as a vacuum reservoir.

/Magnus F.

In principle this is possible, but a regular compressor will vaporize a large quantity of oil when running as vacuum pump and is designed to compress to 150psi. I need only minus 10-12 psi but a higher volume.

The dual piston vacuum pump that I have is specially built for this purpose and oil-less (just too small). That is the nice thing about the roots blower since it uses the oil only for the bearings while the rotors run dry.

I think I will go a bit smaller than the rail car with the reservoir. Maybe an empty propane bottle or just a length of 6" plastic pipe.

[slomove]

Got my new toy :)

Eaton M62 Supercharger off a 3.8l Buick V6.

eBay $59 including shipping from Florida. Can not complain about the price....
And...the rotors are spinning. I had kind of expected something rusted in place but maybe I can just check the oil level and use that thing without bearing rebuild. I tried it with a hand drill and it pumps quite nicely.
Not sure what that little butterfly throttle is about and several small nipples. Probably idle control and vacuum hookup but I can plug them all.

[slomove]

I got my vacuum gadget running.

Good news: it works as expected. I used a 3hp motor from Harborfreight and pulleys to run the supercharger at 2800 rpm. I can get about 15"Hg vacuum (50kPa) before the motor stalls and 10" continuous. Pretty much what I need.

Bad news: That contraption would get me black flagged at Laguna Seca immediately. I measured 100-105dBA from 10 feet away and it sounds like an orchestra of powerful thickness planers. There is no way I can run this in our neighborhood without extremely serious muffler. Oh well, one of my fun projects.

http://www.youtube.com/watch?v=1qAS88-hKIs

[Elv15]

Great progress Gert. Where is the noise coming from? Is having it mounted on a large board acting as a sounding board?

PS: It would make a hell of a flowbench!

[moosetestbestanden]

Dude... that thing sucks! :-D

[slomove]

Great progress Gert. Where is the noise coming from? Is having it mounted on a large board acting as a sounding board?

No, that is actually very common for roots blower used for vacuum. I really don't want to hear a commercial 30 hp unit howling.

It can not be seen but the mounting board has a 4" by 4" cutout where the exit of the supercharger is. Every time one of the six total rotor lobes comes by with a pocketful of vacuum (so to speak) the ambient air rushes in. That happens 300 times per second making for a fabulous air raid siren. In the meantime I rigged up a temporary muffler with a second board under the whole contraption that sandwiches a few baffles and packing material. That cuts already 15-20dBA and makes it almost bearable. I think with a bit more optimization I can use it without getting tarred and feathered by my neighbors.

Dude... that thing sucks! :-D

Yep, that is the whole idea. But it is surprising how much power is needed to operate it. I bet in its intended use as compressor at full engine speed it can easily eat up 10 to 15 hp before generating anything additional.