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Vacuum Bag press minimum psi/ psf

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hunggaur

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hi folks could some please tell what is the minimum psi/psf you can get away with on a pump for a DIY vacuum bag press.

i have got an old vacuum pump up and running which gives 1.933 pis / 248 psf is this enough

Also how does this compare to making your own out of a fridge compressor, what psi do they pull and would i be better making my own ????

many thanks

currently confused

jon
 

Steve Maskery

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Hi John
A lot will depend on what exactly you are pressing. For nice, flat, compliant veneers it will probably suffice, but for curved surfaces or difficult burrs - who knows, you'll just have to suck it and see.

1.9 doesn't sound very much to me. A total vacuum is about 14 psi and my vac pump reaches about 90% of that. SO you are reaching about 1/6th of mine. It's not great, but, as I say it might be enough for some work.

Regarding fridge compressors: Bear in mind when you take it off that you are releasing all sorts of nasties into the atmosphere. Fridges really should be decommissioned properly.
Cheers
Steve
 

Argus

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Steve Maskery":1pzqqhrr said:
Regarding fridge compressors: Bear in mind when you take it off that you are releasing all sorts of nasties into the atmosphere. Fridges really should be decommissioned properly.
Cheers
Steve


Steve is absolutely right. The operators' laws are quite specific with this stuff.

Unless you know exactly what's in it, the refrigerants may be CFCs (illegal nowadays in any form) or HFCs (likewise in unqualified hands) or more than likely these days, a cocktail of Iospropanes which are flammable.

When not used in the fridge itself or the fridge is a dud, the gases are considered Hazardous Waste and require a license for disposal (honest!) It is an offence in the UK to release them to the atmosphere. Similarly the oils in the compressor are hazardous.

Old fridge compressors can and have been used for evavuation purposes, but as a reciprocating (piston type) compressor, in my experience, will shower the whole issue with an oil mist which is difficult to remove and is known to be carcinogenic.


Added to which the motor's windings are intended to be gas cooled (i.e. with the cold refrigerant gasses). Prolonged use pumping air and eventually nothing when you have removed the air, will probably burn it out within a short time.

Finally, the ultimate vacuum is quite poor with these machines in any case.

That's why the commercial pumps use oil-less vane compressors. No oil and a better vacuum.

I'm sure that there's sombody out there who has done it all, survived to tell the tale and will disagree, but it's an all round bad idea.



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hunggaur

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yes i am fully aware of the hazards of fridge compressors but i can prob get my hands on a new one without gas in it
 

9fingers

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If Steve is getting 90%, then that is about 1.4psi you are getting 1.9psi
Not a lot of difference really is there?

Bob
 

TheTiddles

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a few psi is normally all you'd need, getting 10-12psi out of the 14 available is always nice. I normally turn mine down to about 8-10psi as it uses the pumps less. The difference you need between forming large sheets and pressing small veneered box lids will be huge, you'll have to see how it goes

Aidan
 

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