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Sep 14, 2005, 04:55 AM
The reviewer
XJet's Avatar

Home-made $15 vacuum pump


After finding no suitable supplier of vacuum pumps suitable for model-sized bagging, and having found that the environmentalists have made it impossible for broken ones to be given away to would-be vacuum baggers wanting to build their own pumps, I had to take a different tack.

So I wondered if I could convert one of those cheap 12V compressors that you can buy for less than US$10.

The answer is *yes* -- and the converted unit works *very* well indeed.

It'll pull well over 20 inches of vacuum and evacuates a decent wing-sized bag in seconds.

As you can see from the pictures, I had to machine up a new head for the pump so that I could connect my vacuum line to the non-return valve on the intake side of the compressor.

For a vacuum guage, I picked up a cheap turbocharger boost meter that also shows vacuum down to 30 inches (or so it claims).

The pressure regulator is just a piston/cylinder assembly I knocked up on the lathe -- took less than 10 minutes and this uses the vacuum to pull against a simple tension spring to activate a microswitch in series with the motor.

To reduce the amount of cycling, I plumbed an old propane tank into the vacuum line via a tee fitting and when I bagged some wings yesterday with the vacuum set to 10 inches, the pump only ran for about 20 seconds every 10 minutes to maintain the required vacuum.

The whole setup is working far better than I'd hoped and was used on a second set of wings today.

The total cost for setting something like this up could be *very* cheap, especially if you have the tools to do some basic machining (the mods to the head could have been done with just a drill, hacksaw and file) and pick up some of the parts from an auto-wrecker real cheap. You could (for instance) use a modified waste-gate actuator or vacuum-operated ignition advance unit instead of the purpose-built vacuum piston I made.

And, as a bonus, this thing will run off a 12V battery so will hold a vacuum even if the power goes off (are you listening you LA modellers? :-)
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Sep 14, 2005, 01:30 PM
Rat Dude
mwraight's Avatar
Excellent job - and quite creative!
Sep 14, 2005, 09:35 PM
Registered User
Wow awesome job Xjet!

How does the 12V compressor act as a vac??? Is it just a matter of reversing the +ve and -ve pols?

I've also seen a standard surgical syringe used inline to trigger the microswitch or an admission advance regulator from an old car.

How does your 12V power (car battery??) source stand up after 8 hours of use?
Sep 14, 2005, 09:50 PM
The reviewer
XJet's Avatar
These compressors are just a simple piston pump with two non-return valves in the head. All I had to do was make up a bit of metal that fitted over the head and allowed me to bring the intake hole (where the pump normally sucks its air) through to a pipe fitting.

The pump itself just runs as normal except that instead of sucking in surrounding air, it's sucking down the vacuum line I've attached.

It only takes about 90 seconds to create a 10-inch vacuum in the propane cylinder, after which (providing your bag doesn't leak too much) it only runs for about 20 seconds every 20 minutes or so. This means that, over an 8-hour period, the pump only has a total running time of 8 minutes or so -- hardly enough to flatten a decent 12V lead-acid or gell-cell battery.

The little pumps are pretty crude and the only other mod I've made is to cut a small hole so that I can manually oil the bottom bearing on the connecting rod if it gets a bit dry.
Sep 14, 2005, 09:59 PM
Duct Tape and Balin' Wire
Sheer brilliance. I may build this. I have a spare portable air tank laying around I have used like, twice in the past three years or so lol. It held air for a couple years so I know its leak free. Thanks for the great idea!!

BTW, in that vacuum switch you made, is it just a piece of pipe with one end capped off, and a slug, with a machined groove for an O-ring or something? Any more specifics you could post on that lil rig?
Sep 15, 2005, 08:17 AM
Registered User
Ok, here's a $14AU pump compressor pulled to bits. In particular the head. Can you give any advice as to how to you put your 'bit of metal' over the intake to a pipe fitting.

I'm thinking that without being able to machine something that a small copper tube could be inserted and sealed in the intake valve.

Any feedback would be helpful thanks
Sep 15, 2005, 11:50 PM
The reviewer
XJet's Avatar
I just got a small block of aluminum, drilled a hole in the middle then put two hacksaw cuts from the side through to that hole so that I ended up with a U-shaped gap that then cleared the vertical (pressure) non-return valve and the tube that goes off to the pressure guage.

I then marked, drilled and countersunk three holes so that the cylinder retaining bolds would pass through and, when tightened, effectively clamp this block of aluminum onto the top of the cylinder head.

I then marked where the suction hole in the head would fit against the block (a bit of eyeballing required) and drilled a 1/8" hole about 2/3 of the way through the block.

Then, from the side, I drilled another hole that mated up with that first hole. That second hole was also tapped for the vacuum nipple -- but you could also just drill it the right size to take a bit of tubing and use an epoxy or silicone adhesive to hold/seal it.

The bottom of the block was then given a smearing of silicone and some was put around the viertical post containing the pressure non-return valve. Things were bolted together very *lightly* for an hour or two so as to let the silicone cure. Then the three head bolts were torqued down and the mods to the compressor were done.

If you like, I'll take some more (closer) pictures of the block of aluminum I made.
Sep 15, 2005, 11:57 PM
Registered User
Pics would be awesome thanks!!!! Pictures always tell a 1000 words.

I think I've got the general jist of the concept behind the mods.

Thanks Heaps!!
Sep 25, 2005, 06:40 AM
The reviewer
XJet's Avatar
I'm about to start work on a 4 meter (13-foot) wing with a delta center-section that has a root chord of 5 feet -- so that's a *lot* of area and will need a goodly-sized vacuum pump with significantly more pumping capacity than the one I've already built.

Based on the success I've had with the converted 12-V compressor I'm going to modify one of those cheap mains-powered compressors that can be had from any number of sources.

I've actually seen these things selling here in NZ for as little as US$70 and it looks as if the mods will be *very* simple -- perhaps just requiring the head to be removed, rotated 180 degrees, and refitted so that the non-return valves are exchanged and it draws vacuum rather than making pressure.

The already-present tank will act as a great (large) vacuum reservoir too!

Of course a seperate vac-switch will be needed to control the amount vacuum produced but that's a simple job and I'll check to see whether the existing pressure switch might be modified as well.

If anyone's interested then I'll post the steps involved for all to see.
Sep 25, 2005, 06:51 AM
Registered User
Kep the pics and commentary coming

They have these in Bunnings Australia for about $98.
http://www.gmcompany.com/index.cfm?p...C92E9887886383


or these for $69AU, however can run for 30min continuous only.
http://www.gmcompany.com/index.cfm?p...B62B9D45B9B61C
Sep 25, 2005, 05:16 PM
Duct Tape and Balin' Wire
Quote:
Originally Posted by XJet
If anyone's interested then I'll post the steps involved for all to see.

Yes, VERY VERY interested indeed!!!
Sep 25, 2005, 05:20 PM
Duct Tape and Balin' Wire
Quote:
Originally Posted by XJet
I just got a small block of aluminum, drilled a hole in the middle then put two hacksaw cuts from the side through to that hole so that I ended up with a U-shaped gap that then cleared the vertical (pressure) non-return valve and the tube that goes off to the pressure guage.

I then marked, drilled and countersunk three holes so that the cylinder retaining bolds would pass through and, when tightened, effectively clamp this block of aluminum onto the top of the cylinder head.

I then marked where the suction hole in the head would fit against the block (a bit of eyeballing required) and drilled a 1/8" hole about 2/3 of the way through the block.

Then, from the side, I drilled another hole that mated up with that first hole. That second hole was also tapped for the vacuum nipple -- but you could also just drill it the right size to take a bit of tubing and use an epoxy or silicone adhesive to hold/seal it.

The bottom of the block was then given a smearing of silicone and some was put around the viertical post containing the pressure non-return valve. Things were bolted together very *lightly* for an hour or two so as to let the silicone cure. Then the three head bolts were torqued down and the mods to the compressor were done.

If you like, I'll take some more (closer) pictures of the block of aluminum I made.

Actually, I was wondering more about that spring loaded vacuum switch you made. How does the inner "piston" seal to the outer "cylinder"? Is it an O-Ring?
Sep 26, 2005, 01:10 AM
The reviewer
XJet's Avatar
No O-ring was used on mine -- I just bored the female section in my lathe and turned up a piston that was a nice smooth fit. Slop a bit of oil on it and there's no need at all for an O-ring -- it seals like a duck's bottom yet moves with only the slightest amount of vacuum.
Oct 04, 2005, 02:44 PM
Scott Zastoupil
szastoupil's Avatar
Regarding the vacuum switch, I have been trying the same idea but using a veternary syringe from the local Farm and Fleet. I have not had very good luck because the rubber fit is tight and there is a lot of hysteresis with the applied vacuum. For instance the syringe will be stable at 20" of vaccum, but the spring won't move the syringe until it gets down to 10-12". I have also added lithium grease, but that seems to have made it worse. I haven't tried sanding the rubber plug to reduce the static friction, but am concerned that it will create too much of a leak.
Oct 04, 2005, 11:44 PM
Registered User
Hmmm, the glass syringe's work better which you should be able to get from the local pharmacy.

Otherwise the advance regulator valve from an auto store might be your best bet like the one below.

Jason


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