vacuum pump help!

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BradG

BradG

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Ok, I know nothing about these things other than some suck more than others. no twisting those words please.. family site :redface:

Im planning on making a vacuum chamber for degassing, and stumbled across these two pumps:
12V DC 2 STAGE VACUUM PUMP KIT

seemed interesting, and being in modular form would be easier for me to integrate into something.

The second one is this:
1 CFM (45 lpm), 2 Stage Rotary Vane Mini Vacuum Pump | eBay

Though ive no idea with regards to the specs of these units and im curious if the second one is much better than the first seeing as its twice the price, or if even either of these are suitable for degassing
 
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Hi Brad; How are you doing? My consern would be that the 12V pump would require a charger also, plus batterys, unless it comes with a plug in converter. How long could you run it on batterys and hold your vaccuum? The second one is made for AC units, to drain the units of their fluids. What about the 220V? Don't you run on 208V in the UK? Again you may need an adapter. Price is not an object when you want quality equipment that does what you want, is made for that application, and will last with little upkeep. You usualy need about 26 inches of vaccuum to degas effectively. Just my insite. Jim S
 
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I'd say the first pump is not quite adequate enough if you plan on using it for stabilizing. Ideally you would like something capable of pulling around 28-29" Hg. I use a gast 0523 oil less rotary vane pump that I originally got for vacuum chucking and it develops about 28" inches, but I have heard that the best units for stabilizing are the oil-filled type that are used in the AC/refrigeration service industry. They appear much like the second one in your photos, and according to the specs it can pull 30 microns (>29") which looks quite sufficient.
 
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In my opinion, you would not be happy with the 12V unit.

At 30 microns, the second unit will pull all the vacuum you need. But the 1 CFM rate would only be suitable for small chambers when degassing resins. When stabilizing wood, you don't really care if it takes 10 minutes to develop full vacuum. When degassing resins, the faster you can get it done the better off you will be.

Ed
 
I use one of these almost daily for vac chucking when I work (turning). I specifically chose this one because I can use it with resins. Not sure if I have to change the filter or not. No problems so far. They are aimed at the professional joinery shop for vac pressing using resin glues. The company is based in an industrial estate near Downton. (NOT Downton Abbey folks - that is at Highclere near Newbury)

He does sell them without the frame attached, but its useful if you need to move it around at all, especially as they get hot when used continuously for a while. The one my link sends you to is rated for continuous use - so I can have it on all day if I like.

Hope this helps.
 
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Thanks for the opinions guys. price isnt so much of an issue as im not having to twist my arm to save a pound just wanted tol make sure the cheapo one wouldnt perform equally with the other one which ive seen happen in the past with products put into a nice end user casing etc. Having said that Jean, i very much doubt i would get £308 worth of usage out of it to justify it ;) i think £150 would be my upper limit.

I will never stablize wood, only degassing resins.
 
Hi Brad - Fewer microns equals deeper vacuum, so 15 would be a stronger vacuum pump than 30. Here's a link to a table that you might find useful.

http://www.tpwvacuum.com/images/Vacuum Units Conversion Chart.jpg

Once you get below 100 microns, there isn't going to be a lot of difference for resin degassing. Heck, you probably wouldn't notice the difference below 1000 microns, but most A/C pumps that I've seen will pull below 100.

I think you would definitely be happier with 3 CFM vs 1 CFM.

Ed
 
BradG said:
Ok, I know nothing about these things other than some suck more than others. no twisting those words please.. family site :redface:

Im planning on making a vacuum chamber for degassing, and stumbled across these two pumps:
12V DC 2 STAGE VACUUM PUMP KIT

seemed interesting, and being in modular form would be easier for me to integrate into something.

The second one is this:
1 CFM (45 lpm), 2 Stage Rotary Vane Mini Vacuum Pump | eBay

Though ive no idea with regards to the specs of these units and im curious if the second one is much better than the first seeing as its twice the price, or if even either of these are suitable for degassing
Click to expand...


Hi again Brad o' the Fylde ',;~}~

If your alright money-wise WRT obtaining a pump, then I've likely got no advice for you since I've never bought one, but if you're after something from cheap to free, then my experiences and advice may be of some use.


Having always been beyond 'broke' and also loving to make the things I need rather than buy, if within my scope, I went down the converted refrigeration pump route.

Started years ago when I reclaimed a dumped portable room dehumidifier and nicked the pump - realised back then that these things sucked like billeo, so when I wanted to start trying to stabilse pieces of rotten spalted wood and stuff I dug it back out.

So after sucking acrylic or similar plastic dissolved in acetone right into the unit, that died. Ordinary fridge pump from e-bay £10 worked for months for pressure and vac. but I had a mate who had a mate who worked in a catering supplies/repair place, and cadged a much bigger one (about 1/2 again to double sze of a home fridge compressor) - still the same thing - oval-ish, sealed cannister and quiet (they are actually nearly all dual *piston* pumps these days - rotary-vane are /rare/)

Anyways to not make a long story much<cough> longer - I started using this for vacuum and it's a beast - empties 15L container down to 28-29 Hg (you're almost at sea level there and we aren't that much higher - 29-ish is about all you get) in about a minute. It's so well built it shold go on forever providing I keep the oil topped up (you can drain the special refrigeration oil and just fit decent middleweight motor oil - much better. I even put slick 50 in mine LOL)

Mine just runs through some stiff hose glued to a rubber homebrew bung, and that gets stuck through a tapered hole in my vac. pot - doesn't leak much at all.

Made a few mods to mine:

1st I have a transparent trap cannister in-line - pull any bits of liquid in it settles there rather than inside the pump - saved me a few times!

Other thing is a home made vacuum switch - I copied the rough Idea I found on the web using microswitch, car vacuum advance unit and tough spring (but I converted a camping gas regulator and made a titanium leaf spring) - it's adjustable and fairly accurate - drops an inch or 2 hg belw where you set it, then she fires up again and pulls the vacuum back down.

So just another avenue to consider if you're prepared to mess about a bit.

Having looked at the 2 links above, I do though have 'opinions' (and remember 'opinions' are just 'onions' and 'pi') - that first one I wouldn't touch - it's not last and will be noisy as hell - those little 12 v brushed motors run at high current and get hot after a short while - only really meant for short work or lower loads - would call it 'sub-hobby-grade'. Think of 2 12v tyre inflators running together.

2nd one looks great for the price and if protected against drawing up foaming resin and kept oiled should last you a long time.

Again ^IMO^

FlowolF - Pls. ignore irrelevancies, heheheh...
 
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plantman said:
Hi Brad; How are you doing? My consern would be that the 12V pump would require a charger also, plus batterys, unless it comes with a plug in converter. How long could you run it on batterys and hold your vaccuum? The second one is made for AC units, to drain the units of their fluids. What about the 220V? Don't you run on 208V in the UK? Again you may need an adapter. Price is not an object when you want quality equipment that does what you want, is made for that application, and will last with little upkeep. You usualy need about 26 inches of vaccuum to degas effectively. Just my insite. Jim S
Click to expand...

Ed thanks for the info :) 3cfm it is then.

Mark, thanks for the link il go and read it.

Flowolf no i know the pitfalls ofr using compressors out of fridges etc. I much rather prefer to buy products made for the job than trying to do it on the cheap.
 
I have a automotive style pump I bought with intentions to do some casting .. never been out of the box.. I would sell if the price is right.
 
I think postage to the UK wouldbe a touch excessive, but may be a state side member which is looking too? :)
 
A higher CFM pump WILL NOT reduce the amount of time it takes to pull down a chamber UNLESS you use a larger diameter hose. A typical 1/4" diameter vacuum hose will only allow approximately .75 CFM to pass through it. If you want to evacuate quicker, you need a larger diameter hose with equivalent properly sized fittings and use the 3/8" port on your vacuum pump. If you are using the 1/4" port, larger size hoses will not make a difference and a higher CFM pump will NOT pull down quicker! My advice, save you money and buy a good quality pump with a good vacuum rating and forget the CFM rating.
 
MesquiteMan said:
A higher CFM pump WILL NOT reduce the amount of time it takes to pull down a chamber UNLESS you use a larger diameter hose. A typical 1/4" diameter vacuum hose will only allow approximately .75 CFM to pass through it. If you want to evacuate quicker, you need a larger diameter hose with equivalent properly sized fittings and use the 3/8" port on your vacuum pump. If you are using the 1/4" port, larger size hoses will not make a difference and a higher CFM pump will NOT pull down quicker! My advice, save you money and buy a good quality pump with a good vacuum rating and forget the CFM rating.
Click to expand...

Curtis - My real world experience is I get to max vacuum a lot faster with a higher CFM pump. (Fair disclosure: This is based on a comparison of two pumps (comparable vacuum ratings), not a large population.) Once you are below atmospheric pressure in the chamber, the air hose capacity at 1 ATM is no longer relevant, is it? You can't talk about capacity without talking about the pressure in the system (whether compressed air or vacuum).


And why would somebody use the smaller port anyway?

Ed
 
Brad, I know you're not short of a bob or two, but if you would like to try before you buy, then I can lend you either ( or both ) a good Robinair oil filled vac pump or a Dilo dry vac pump. You'd just have to pick them up. I haven't used them for some time and you could use them for a month or so.


The obvious question is: Do you actually need vac?
 
Thanks Curtis, duely noted.

Steve, thanks for the kind offer and if you were in blackpool id most probably take you up on the offer :wink:

As to do i need vac? most probably not. will i buy one anyway? most probably yes. as when you see what im up to you will see why i have the sudden desire to cast in clear but its got to be perfect... the smallest bubble would cause me big issues. based on this its worth having a decent pump in the shop
 
No probs Brad. It's an open ended offer, just let me know.

Next question;

Why do you think that a vac, rather than pressure is the key to the problem?

Theoretically, the best you can hope for in a vac chamber is minus 1 bar ( or Zero bar absolute, if you prefer :wink:)
This in theory, will make the air bubbles expand to twice their size and thus ( hopefully ) float harmlessly to the surface of the setting resin.

Pressure on the other hand is a completely different beast. Also 'theoretically' the limit is restricted only by your equipment.
But you can crush those little suckers into oblivion by applying 'several' bar pressure. The only snag is that you have to maintain the pressure untill the resin has fully set.

I have NEVER had bubbles in resin that has been allowed to set at atmospheric pressure ( hence the lack of use of my kit ) and I have cast clear stuff too.

I personally think the issue with bubbles are those that are stuck to the surface of the item you are casting, rather than in the resin mix.

Now, lets say you are casting something that has under-cuts where pockets of air can get trapped. Vacuuming will expand those air pockets and, at best, HALF of it will spill out and float away.
With say 4 bar pressure that same void will be only a quarter of it's size.

If I knew then, what I know now, then I'd forget the pressure pot AND the vac pump and just have the resin setting in molds on a work bench with MAYBE a machine, like a drill press, running to create a small amount of vibration.

The secret is to STIR the resin, not whisk:wink:

Do you know how to make an Irish Coffee? Pour your resin over something as it enters the mold. 99/100 success rate.:biggrin:
 
I only use an ultrasonic cleaner with a heater which heats the water and in turn heats the resin and thins it down. The warmer the resin the shorter the time for the polyester resin to begin to gell. I "wrangle" any air bubbles I see away from whatever I have glued to the kit tube. So, yes to your answer to about vibration...the ultrasonic cleaner produces vibration that causes the air to form bubbles and rise to the top. Vibration tables are used by some or even the table of a table saw or band saw with the saw running. Be aware that I use polyester resin so I can't comment on these tricks working with other resins.
Do a good turn daily!
Don


BradG said:
its_virgil said:
Brad,
This thread may be of interest to you, especially what GrassScratcher has to say. Too much vacuum on polyester resin can be detrimental.
http://www.penturners.org/forum/f43/vacuum-pressure-recommendation-51895/

I no longer use vacuum nor do I use pressure for polyester resin. Many still do. Looking forward to what you have up your sleeve.
Do a good turn daily!
Don
Click to expand...

Thanks Don il take a read. do you just rely on vibration to remove bubbles?
Click to expand...
 
parklandturner said:
MesquiteMan said:
A higher CFM pump WILL NOT reduce the amount of time it takes to pull down a chamber UNLESS you use a larger diameter hose. A typical 1/4" diameter vacuum hose will only allow approximately .75 CFM to pass through it. If you want to evacuate quicker, you need a larger diameter hose with equivalent properly sized fittings and use the 3/8" port on your vacuum pump. If you are using the 1/4" port, larger size hoses will not make a difference and a higher CFM pump will NOT pull down quicker! My advice, save you money and buy a good quality pump with a good vacuum rating and forget the CFM rating.
Click to expand...

Curtis - My real world experience is I get to max vacuum a lot faster with a higher CFM pump. (Fair disclosure: This is based on a comparison of two pumps (comparable vacuum ratings), not a large population.) Once you are below atmospheric pressure in the chamber, the air hose capacity at 1 ATM is no longer relevant, is it? You can't talk about capacity without talking about the pressure in the system (whether compressed air or vacuum).


And why would somebody use the smaller port anyway?

Ed
Click to expand...

Ed,

My experience has been directly opposite yours. I have a Robinaire 3 CFM and a JB 6 cfm pump. I have hooked them up to the exact size chamber using exactly the same fittings and tubing and timed both. They both got to 28.5" Hg within a fraction of a second of each other.

Remember, with vacuum you are sucking and as such, it is completely different than using pressure. You are creating a void of some sorts and expecting air to flow to that low pressure side at atmospheric pressure or less. Do some reading on some HVAC technician forums and you will see that small hoses only allow a set amount of air movement through them under vacuum.
 
its_virgil said:
Brad,
This thread may be of interest to you, especially what GrassScratcher has to say. Too much vacuum on polyester resin can be detrimental.
http://www.penturners.org/forum/f43/vacuum-pressure-recommendation-51895/

I no longer use vacuum nor do I use pressure for polyester resin. Many still do. Looking forward to what you have up your sleeve.
Do a good turn daily!
Don
Click to expand...

Hi Don - Styrene has a relatively low vapor pressure and a relatively high boiling point. Under vacuum it will start to boil off after the air and water have been removed from the resin. As long as air and water are coming out of solution they should keep the system pressure at a point where styrene isn't. The resin has a very different look to it when the styrene starts to boil. Bigger and shinier bubbles is how I would describe it, but there is a definite change when it happens. With a 6 CFM pump on a vacuum chamber that is about a cubic foot, I get the resin degassed in about a minute. Used to take much longer when I had a pump with lower CFM.

I watch my resin as it degasses. Firstly to insure I don't get a foam over. Secondly, as soon as it hits the point where it looks like styrene is coming out I turn off my pump and open the air valve. I probably lose a little styrene, but not enough to make a difference in the PR. From talking to the folks at US Composites I was left with the impression that the amount of styrene in PR can be pretty variable and the exact proportion isn't critical.

So I would agree that too much vacuum is bad for PR, but there is no reason to apply too much.


Ed
 
skiprat said:
No probs Brad. It's an open ended offer, just let me know.

Next question;

Why do you think that a vac, rather than pressure is the key to the problem?

Theoretically, the best you can hope for in a vac chamber is minus 1 bar ( or Zero bar absolute, if you prefer :wink:)
This in theory, will make the air bubbles expand to twice their size and thus ( hopefully ) float harmlessly to the surface of the setting resin.

Pressure on the other hand is a completely different beast. Also 'theoretically' the limit is restricted only by your equipment.
But you can crush those little suckers into oblivion by applying 'several' bar pressure. The only snag is that you have to maintain the pressure untill the resin has fully set.

I have NEVER had bubbles in resin that has been allowed to set at atmospheric pressure ( hence the lack of use of my kit ) and I have cast clear stuff too.

I personally think the issue with bubbles are those that are stuck to the surface of the item you are casting, rather than in the resin mix.

Now, lets say you are casting something that has under-cuts where pockets of air can get trapped. Vacuuming will expand those air pockets and, at best, HALF of it will spill out and float away.
With say 4 bar pressure that same void will be only a quarter of it's size.

If I knew then, what I know now, then I'd forget the pressure pot AND the vac pump and just have the resin setting in molds on a work bench with MAYBE a machine, like a drill press, running to create a small amount of vibration.

The secret is to STIR the resin, not whisk:wink:

Do you know how to make an Irish Coffee? Pour your resin over something as it enters the mold. 99/100 success rate.:biggrin:
Click to expand...

Hi Steve - Degassing of resin will remove all the air from the resin. Careful handling of the degassed resin will allow you to cast bubble free without vacuum or pressure at your leisure. If you use pressure, you have to keep the resin under pressure until fully cured (not a big deal with urethane resins, but can take a lot of time with PR). This can be a major disadvantage in a number of situations (e.g. rotocasting).

Taking air from atmospheric pressure to anything close to full vacuum (aka -1 bar) will increase the size of air bubble way more than double. Every halving of the pressure will double the volume (other things being equal). Going from 1 bar to zero bar involves many more than one halving of pressure.

Whether vacuum, pressure or neither is ideal will depend on what is being done. Vacuum and pressure each have their place when working with resins. Neither is ideal for everything.

Ed
 
its_virgil said:
Brad,
This thread may be of interest to you, especially what GrassScratcher has to say. Too much vacuum on polyester resin can be detrimental.
http://www.penturners.org/forum/f43/vacuum-pressure-recommendation-51895/

I no longer use vacuum nor do I use pressure for polyester resin. Many still do. Looking forward to what you have up your sleeve.
Do a good turn daily!
Don
Click to expand...


Same situation with the PU formulations supplied by ABL Stevens over here - too much vac and/or for too long during degassing and it suddenly foams rapidly with quite a large exotherm, then sets solid in seconds, and this is with a system (PU-50, 1:1.1 mix) that usually takes 18-22 hours to set-up at ~21C. Still made a fantastic dispenser cup shaped conglomerate of frozen crystal clear bubbles.

I asked Jeff at ABL about it in case it was a contamination issue on my part when he clarified that it's down to boiling off some of the more volatile elements of the mixture - presumably elements that slow/control the rate of the cross-linking reactions - no higher than around 26/27 Hg and no longer than 5 mins under vac, he explained, but this stuff's so runny when mixed and warmed to about 25-30C plus the long cure time - it makes great bubble free castings with little effort anyway.

FlowolF
 
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