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Vacuum Pump

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Created by cammd Two weeks ago, 8 May 2019
cammd
QLD, 2239 posts
8 May 2019 8:19AM
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I would like a vacuum pump for repairs etc, is it better to build one from a fridge compressor or buy one off ebay. Ideally I would like it to be able to maintain a set vacuum automatically, so it would need to cut in and out. I guess either way some mods would be needed to either the bought or recycled option.

What do people use and how do they set them up, do you use a regulator to maintain pressure or just a bleed off valve, do you use a tank or chamber to act as a "buffer" for pressure and also capture moisture or resin. Hoping for some good advice or even some guidelines or instructions on how to set it up.

Imax1
VIC, 1867 posts
8 May 2019 8:33AM
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All good questions , im also interested.

olskool
QLD, 1283 posts
8 May 2019 8:53AM
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^ x 2.
Have a sacrificial fridge waiting

FormulaNova
NSW, 8643 posts
8 May 2019 9:11AM
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Select to expand quote
cammd said..
I would like a vacuum pump for repairs etc, is it better to build one from a fridge compressor or buy one off ebay. Ideally I would like it to be able to maintain a set vacuum automatically, so it would need to cut in and out. I guess either way some mods would be needed to either the bought or recycled option.

What do people use and how do they set them up, do you use a regulator to maintain pressure or just a bleed off valve, do you use a tank or chamber to act as a "buffer" for pressure and also capture moisture or resin. Hoping for some good advice or even some guidelines or instructions on how to set it up.


I bought two off of ebay. Two because I don't like the idea of one failing just after I have setup a project and the pump fails... not that they ever have.

I think ultimately the fridge compressors fail due to lubrication problems. I killed one when i first started playing with them.

I built a setup which uses a voltage sensitive switch and a car MAP sensor to hold the pressure where I want it. I don't know what everyone else uses, but essentially it turns on the pump when the voltage from the MAP goes beyond what it is supposed to.

I use a car vacuum gauge to tell me what pressure I have.

I found that some sort of reservoir helps a lot to prevent the pump cycling a lot. In the end I used a length of 100mm PVC with airline fittings tapped into it and a t-piece.

I haven't used it in a while, but I can't remember what I used as a trap, but I think I had a smaller section of pressure rated PVC pipe with two airlines tapped to it and a stopcock at the bottom to drain off any water.

It will be interesting to hear how others regulate the pressure.

decrepit
WA, 9114 posts
8 May 2019 8:50AM
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I have a pump controlled by this little device,
au.rs-online.com/web/p/pressure-sensors/0407221/
It's very sensitive, so wouldn't give the motor time to get up to speed before switching off again, if there's isn't an inbuilt delay in the cct.
I thought a big reservoir would be enough, but I've had to add a delay cct into the relay that in turn switches a contactor.
I have one of those big domestic gas bottles as a reservoir, and an old automotive vacuum gauge.

I started with a fridge compressor, but was told that overheating is the problem. They are designed to run with the return coolant aimed at the motor. In vacuum mode there's no return. The advice was to cut them open, to allow natural airflow around the motor, but this was a disaster, as the window above the pump smashed in a storm and filled it up with water. It didn't work very well after that!!!!
I was convinced that with a good reservoir and short duty cycle overheating wouldn't be a problem, so next one remained closed and worked fine. Until a mate used it, punctured the bag while getting the wrinkles out and couldn't quite seal it up again. So the pump was going continuously, overheated and burnt out.

In the past, a post here described using an old ignition advance/retard distributor mechanism to activate a switch, this probably has enough inbuilt delay, and is the way I'd go if starting from scratch.

cammd
QLD, 2239 posts
8 May 2019 12:30PM
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Fridge compressor sounds a bit sketchy so I am thinking a new pump is the way to go.

What size pump if buying a new one, 3cfm, 6cfm, single stage or 2 stage pump ??? they range in price quite a bit and some come with chambers and gauges, based on experience what's a good size to start with.

decrepit
WA, 9114 posts
8 May 2019 10:58AM
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Once you've reached the desired pressure, and have a good seal, a very small pump should be all you need.
I normally have a duty cycle of 5 seconds on, 3 minutes off.
It's just the bigger the pump, the quicker you get to the desired pressure. Of course this will also depend on how much volume, you're dealing with.
As I have such a big reservoir, I pump that down first, that also helps to suck air out of the bag. I'd say 3cfm single stage is OK, (if that's 3 cubic feet/minute)? Unless you have a huge vacuum bag that's not going to take long. I think 1cfm would be adequate.
I've no idea what capacity mine is, but it says it's single stage.

I think multiple stages will get you a harder vacuum, which you definitely don't want!
I run about 1/3 to 1/4 atmosphere, much more than that will compress the core foam. Even if you're making solid fins a single stage should get so close to 1 atmosphere it doesn't matter.

cammd
QLD, 2239 posts
8 May 2019 1:07PM
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Thanks good info

When trying to dry a board do you put a hole up one end and the vacuum pump at the other to suck the moisture through or just apply a vacuum to an otherwise sealed board

jirvin4505
QLD, 1010 posts
8 May 2019 1:15PM
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I've used fridge motors for many years. Often run continuos when doing composite aeromodelling stuff into Molds. Fan running on motor has allowed them to survive 30+ years with the odd top up of oil

ive also used the car vacuum advance thing with white foam - sometimes it gets fiddle and unreliable - much better pressure gauges avail today

fortune smoked on me and I ended up lately with hospital anaesthetic pump. Set and forget.

If if I was starting out would probably save my money and use fridge motors - cheap as and reliable if not cycled too much. Running continuous with a bleed and fan cooled would probably last forever.

Cheers Jeff

cammd
QLD, 2239 posts
8 May 2019 1:24PM
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I'm thinking this seems ok for starters

www.amazon.com.au/BACOENG-Vacuum-Chamber-Single-Stage/dp/B07GGPMDQM/ref=asc_df_B07GGPMDQM/?tag=googleshopdsk-22&linkCode=df0&hvadid=341791790585&hvpos=1o2&hvnetw=g&hvrand=2128958815002131976&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9069066&hvtargid=pla-728040936927&psc=1

FormulaNova
NSW, 8643 posts
8 May 2019 1:28PM
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My understanding is that 2-stage pumps are meant to do the bulk of the work, and then switch to the second phase once the vacuum gets down a bit. From what i recall they are very expensive compared to normal ones used for car aircon work.

My second pump was bought from a guy on ebay, around where I live, that also does car aircon work. It came with the gauges for aircon work and the hoses, but the bonus is that it came with a threaded fitting that fitted the hoses and I tapped that into the PVC to convert from the aircon fittings to normal airline fittings.

I can see the benefit though of a 2-stage pump as sometimes you have a large volume of air to get down and sometimes you don't find the holes until the bag is mostly down, which is hard if there are holes...

I came up with a cheap solution and use an old vacuum cleaner connected to the vacuum circuit via a shut off valve. The idea is that it sucks the bag down a lot and then the vacuum pump is used to pull it down the rest.

If you are lazy like me and reuse the bag, you end up with bits of tacky tape to block holes.

I have been meaning to build a proper Arduino based controller for this setup, but I never seem to find the time.

decrepit
WA, 9114 posts
8 May 2019 11:50AM
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I think an inlet hole at the top, and the vacuum pump at the bottom is best, especially if you don't know where the water is. I use a water trap in the vacuum line so water doesn't get in the pump, and so you can see what's happening.

If it's a new ding and the water hasn't travelled far, you can get away without making an extra inlet hole.
Make the ding the lowest point and attach the vacuum there, even better if you can leave it in the sun at the same time. This may need a bit of cycling, as the initial flow will be good, but then the flow stops, and you're relying on evaporation. Slowly letting air back in and sucking again will speed things up. Just depends on how much you don't want to make that extra hole.

That compressor looks like it will do the job, and it comes with a small tank, but I'm not sure how useful that will be.

Mark _australia
WA, 19099 posts
8 May 2019 6:19PM
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Nah keep it simple unless you are doing heaps of work.

$150 eBay one (oil / vane pump)

Have a bleeder valve. Just a ball valve will do.

Adjust bleeder to maintain same vac. It takes say 15mins of fiddling to get it steady, but that's how long u take cleaning up after laminating anyway.

If you want to be fancy, use a $20 power point timer to turn it all off after cure. A reservoir helps, 9kg gas bottle is about enough.

Oh and use an old-school car petrol filter in line so it can't suck resin through your bleeder valve.

The advantage here is you don't care about minor leaks in the system as you are inducing a leak yourself!

Technically this is all wrong as the pump is not supposed to run for a long time at less than full vac, but the difference between 15"hg and 30"hg is bugger-all to the vac pump. I've done the above for a lonnngggg time and not buggered up a pump.

DarrylG
WA, 185 posts
8 May 2019 6:39PM
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I have made a couple and all still working but they don't do a lot of work. I wire everything to a power point so easy and quick to swap over pumps if one fails.







Mainly just use the fridge compressor, nice and quiet, only runs for about 10 sec every couple of minutes with an old bag

hoop
WA, 1563 posts
8 May 2019 6:57PM
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The cool thing about a good vac pump set up is that it always looks really sinister like something from a meth lab or a time bomb. My set up looks like "Big Boy" that was dropped on Hiroshima.
I'll post some pics tomorrow.

HangOver
3 posts
8 May 2019 8:03PM
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This is a good guide I used when putting mine together.
www.joewoodworker.com/veneering/EVS/concept.htm

I use a cheap ebay pump and find it's much better with the vacuum switch and reservoir, with just the pump I found it gave a lot of fine oil mist out of the exhaust once it got to a decent vacuum level. Covered everything in the garage with a nasty greasy coating :(

cammd
QLD, 2239 posts
8 May 2019 10:14PM
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HangOver said..
This is a good guide I used when putting mine together.
www.joewoodworker.com/veneering/EVS/concept.htm

I use a cheap ebay pump and find it's much better with the vacuum switch and reservoir, with just the pump I found it gave a lot of fine oil mist out of the exhaust once it got to a decent vacuum level. Covered everything in the garage with a nasty greasy coating :(


Where did you source the vacuum switch from

R1DER
WA, 1202 posts
8 May 2019 9:54PM
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Been using the same fridge pump for 20 years or more. I initially used to put an ice cream container full of frozen water balanced on top of it with a small fan blowing on it. now days I dont bother, let it run 10 plus hours and on 40c days, just keep it topped up with car oil before each running. I control vac pressure with a car vacuum gauge for me to read and a ball valve to bleed air into the line to reduce the vacuum. I know another guy who used to top his up with automatic fluid oil Im not sure why but it worked for him.

iCarbon
QLD, 187 posts
9 May 2019 11:43AM
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The setup I use is as follows:
Thomas vacuum pump Model No. 2688CHI44-194 which comes complete with its own pressure regulator, vacuum gauge and water trap/filter.
Air reservoir - 2 x 100 diameter PVC DWV x 300 long heavy duty sewer pipe with caps.
Vacuum gauge - ex measuring car inlet manifold vacuum.
Vacuum bag connector - similar to tyre valve stem without valve.

I was quite happy when I ditched the fridge motor system and changed to this setup. The oil smell emitted from the fridge motor system was terrible, especially when you are running the system overnight.

I let mine run continuously.
I previously had a system which cycled on/off with pressure switches and relays. Its design was based on Joe Woodworkers concept. The complication and cost wasn't worth it for my infrequent usage. Joe Woodworkers design is Rolls Royce.









iCarbon
QLD, 187 posts
9 May 2019 12:16PM
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Select to expand quote
cammd said..

HangOver said..
This is a good guide I used when putting mine together.
www.joewoodworker.com/veneering/EVS/concept.htm

I use a cheap ebay pump and find it's much better with the vacuum switch and reservoir, with just the pump I found it gave a lot of fine oil mist out of the exhaust once it got to a decent vacuum level. Covered everything in the garage with a nasty greasy coating :(



Where did you source the vacuum switch from


I sourced parts for Joe Woodworkers type system from veneersupplies.com as referenced in Joe's article.

Mark _australia
WA, 19099 posts
9 May 2019 11:29AM
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Yes we do need pics Hoops - yours looks like a nuclear weapon for sure

:)

cammd
QLD, 2239 posts
9 May 2019 1:38PM
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Can you use a normal compressor regulator or must it be specialised for vacuum

airsail
QLD, 326 posts
9 May 2019 2:07PM
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Fried my eBay bought vac pump, just got too hot. Some type of storage tank is probably the go so it doesn't run full time.
There are some very quiet compressors being sold, matched with a venturi may be a good option.

decrepit
WA, 9114 posts
9 May 2019 12:47PM
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cammd said..
Can you use a normal compressor regulator or must it be specialised for vacuum


Interesting thought. I think you'd have to connect it back to front, but I can't get my head around, if that would actually work.

I have a feeling when I was first setting mine up I played around with an LPG regulator but abandoned the idea. It's too long ago for this old brain to remember any details.

iCarbon
QLD, 187 posts
9 May 2019 7:36PM
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Why auto cycling systems may need to be complicated:-

www.joewoodworker.com/veneering/EVS/what-and-why.htm

iCarbon
QLD, 187 posts
9 May 2019 7:57PM
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Select to expand quote
cammd said..
I would like a vacuum pump for repairs etc, is it better to build one from a fridge compressor or buy one off ebay. Ideally I would like it to be able to maintain a set vacuum automatically, so it would need to cut in and out. I guess either way some mods would be needed to either the bought or recycled option.

What do people use and how do they set them up, do you use a regulator to maintain pressure or just a bleed off valve, do you use a tank or chamber to act as a "buffer" for pressure and also capture moisture or resin. Hoping for some good advice or even some guidelines or instructions on how to set it up.


Cam

Check out what "The Board Lady" has to say on her website on vacuum systems, bleed off valves, standby pipes to stop pump ingesting resin and salty water.

www.boardlady.com/vacuum.htm

Imax1
VIC, 1867 posts
9 May 2019 8:00PM
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This is way more complex than I expected . I thought you could simply buy a all in one unit and away you go .
So does everyone that vac baggs have some home made mad scientist contraption ?
Some of these contraptions look more complex than the board itself !

Mark _australia
WA, 19099 posts
10 May 2019 7:02AM
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You can buy an all in one - bit ideally need a reservoir and the cheapest all in one is around $500

cammd
QLD, 2239 posts
10 May 2019 12:25PM
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I have ordered a cheap ebay one for now, just going to make up a manifold with a bleeder valve and gauge to regulate vacuum and also make a water trap for starters, there doesn't seem to be a point in having a reservoir if the pump is not cycling on and off. Correct if I'm wrong on that point.

airsail
QLD, 326 posts
10 May 2019 2:05PM
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My cheap eBay vac pump got very hot running full time, had a fan on it to try and keep it cool. It started spewing oil then eventually died, probably didn't like no airflow through it.

decrepit
WA, 9114 posts
10 May 2019 3:02PM
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No reservoir needed if running full time with a bleeder valve.

And I'd think that the bleeder would allow enough air through to keep it cool???

Maybe the cheap ones are just designed for small packaging jobs, that don't take very long?

Any way, keep an eye on it. If it runs too hot, you can add the reservoir and regulator later. As long as it doesn't die the first time.

If you use normal setting resin instead of the slow variety, the resin should be set enough after about 6hrs if it's not too cold. Just don't leave it on overnight.



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"Vacuum Pump" started by cammd