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Old Aug 18, 2011, 09:56 PM
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dydx's Avatar
Brisbane, Australia
Joined Mar 2006
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Vacuum Pump Concept and Demo

Hi Folks

Devising a vacuum pump system is one of the first steps I have taken into the world of composite fabrication esp. vacuuming bagging.

The vacuum pump I've developed is based on a car tyre compressor. I've seen quite a few examples of this on these forums and elsewhere and it seemed like a fairly accessible and cost effective path to take. (if a fridge compressor turns up I might look into that - but I haven't been able to source one for cheap and am a little scared of 240V).

The pump pulls a vacuum of ~23''hg and assuming I can plug some of those leaks should be able to hold it so the pump doesn't need to run all that often. After running the pump for 5mins in the sealed pipe vessel the pump and piston was warm to touch at about 40degC. Running the pump in open air for 5mins while blocking the pressure outlet so that the system was under some stress resulted in about 40degC as well. Based on this, I'm not too concerned about the pump overheating and seizing up and long as it doesn't need to run continuously.

When using the on/off switch to regulate the vacuum by hand (with a good seal on the pipe prior to filming), I was able to maintain 15''hg by cycling on for about 5secs every 40secs.

The next step is to develop a pressure switch in order to maintain a constant vacuum of ~10''hg for white foam and ~15''hg for blue foam. From what I've read, these are the levels I should aim for.

Please let me know what you think and how well you think this will work, is there anything I'm overlooking?

Vacuum Pump Demo (10 min 6 sec)


Cheers
Pete
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Old Aug 18, 2011, 11:54 PM
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DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
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Looks good Pete.

I use a freezer pump triggered by a 5A 240v vac-switch from ACP. It was $75 but heard you can get similar for a lot cheaper on eBay. The switch came with instructions so despite having reservations about 240v (same as you) I wired it up and it worked safely. I don't use a reservoir either. Bought one 2nd hand but it works fine without.

I've used it for 3 wings/ 2 tails and it's been faultless. I use aquarium tubing for the system and the inlet into the bag is simply a small hole supported by blu-tac.

HTH,
Chris.
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Old Aug 21, 2011, 03:51 AM
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Bellingen NSW Australia
Joined Aug 2008
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There are several threads on these forums describing how to devise and wire up a regulator for your vacuum supply.
Mine uses junk parts and only cost the price of the capacitor accross the micro switch points.
Do a quick search and you will find some. If you have difficulty, let us know and I will have a look. I have contributed to more than one myself, so I know they are out there.

Jim.
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Old Aug 21, 2011, 07:51 AM
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Canada, ON, Puslinch
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I get a kick out of this guys vaccum switch http://www.rcgroups.com/forums/showt...=vaccum+switch
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Old Sep 04, 2011, 06:08 AM
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Brisbane, Australia
Joined Mar 2006
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Regulator Complete

Thanks everyone. I've completed the regulator now. Just need to tidy things up and I should be ready for the next phase.

Any comments on the progress so far would be welcome.

The next phase will be getting some plastic and breather material, sealing things up, connecting the hose somehow. (suggestions on ways to do this would be appreciated)

Cheers

Vacuum Regulator (8 min 54 sec)
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Old Sep 05, 2011, 02:00 AM
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Ward Hagaman's Avatar
San Diego
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It's a little crude, but you can seal plastic with a caulking gun and the cheapest latex caulk you can buy around the perimeter. You can seal around the hose as well with a big gob of the caulk as well. Works well for big jobs where you don't want to (or can't) use a sleeve type bag.
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Old Sep 05, 2011, 05:15 AM
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I played around with puddy and sheets of poly enough to learn that the proper clips are worth the money unless you need a large bag [like Ward mentioned above.]

http://www.cstsales.com/vacuum_bag_seal.html
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Old Sep 13, 2011, 04:12 AM
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Auckland, New Zealand
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dydx: would you be able to grab a multimeter and tell me how much current your pump draws during operation? I'm looking at building a micro controller based pressure switch, but need to know how big the relay I need is.
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Old Sep 13, 2011, 04:46 AM
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Brisbane, Australia
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jameotron: its a 12V compressor and draws 3 - 5A when running depending on load. But the inrush current spike for these pumps can be really high. I don't have a way of measuring this, but was going to look into a spark suppression circuit:

How are you planning a micro controller system? My first thought was to use an arduino with some kind of pressure sensor, but I could not find any thing cheap that would be suitable for a high vacuum (this was the closest cheap sensor I could find).

If you did have some kind of sensor that would be awesome. You could program hysteresis, log the cycle times, send SMS's if there's a leak, monitor vac-bagging progress remotely. . That kinda thing is more in my realm of expertise, its composites that confuse me.
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Old Sep 13, 2011, 04:14 PM
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Well, I was looking at the Freescale MPXV6115VC6U. According to the datasheet it is sensitive from 0 to -115kPa (~33"hg). Output is a simple 0 to 5V voltage level that can be sampled with an ADC pin. I can throw together a breakout for it, hook it to my Uno. I was also thinking a two-line LCD and buttons for selecting target pressure, and cycle duration (ie be able to set 300hPa (~10"hg) for 48 hours) and hit start and have it automatically handle the whole process. Probably want a piezo buzzer too.

I'm wanting to convert a fridge compressor, but I will be adding a decent sized vacuum reservoir to reduce the duty cycle of the compressor. For my application I will be wanting to use a relay to control the 240VAC mains supply, but for you you may be able to get by with a darlington pair. You might want to do something smart like use two and have one charge up a largish cap to handle your startup current and another to connect the load once the cap is charged.

Let me know if you want to work together to design a board - I have been making them for my other project (axe.io) and it's pretty cheap if you're making a small footprint board.

Also, regarding the board you linked to on DIY drones, 2kPa is only about 0.5"hg, so it's not up to the job.
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Last edited by jameotron; Sep 13, 2011 at 04:18 PM. Reason: adding extra about MPXV7002DP
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Old Sep 14, 2011, 10:29 PM
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Actually, this looks like a better bet. Connect one side to the vacuum and leave the other open to atmosphere. It will give you an analogue voltage corresponding to the pressure differential between the two. Although it will need an opamp because the maximum voltage output is only 40mV.
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