Need some info on vacuum pumps please(for use in a Vacuum frame)

[Daniel Stone]

hey guys,

well, it seems I might have come across a vacuum frame, without a pump mind you), but still a frame none the less. I'm still not sure of the size, but since I'll need a pump anyhow, and after searching though the threads here and on Apug, I'm stilll kinda stumped as to which one will be best.

currently I'm only working with 8x10 negatives, and 11x14 paper for proofsheets from roll-film negatives, but if this frame is somewhere in the size-range of 20"x24", will I need a pump that's meant to handle something that big?

currently I'm watching some GAST pumps on ebay, like the following:

http://cgi.ebay.com/GAST-OILLESS-ROT...item2eb2770378

http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

http://cgi.ebay.com/Gast-Oilless-Dia...item3a6215a0a1

I'm still a little "fuzzy" on whats needed. I know that I'll need to get a vacuum pressure gauge, if there isn't one already installed on the frame itself...

or just an in-line one with an adjustable bleeder, in order to maintain the same, consisten pressure all the time while printing.

if anyone could lend some expertise on this issue, it would be much appreciated !

my 1st order of Lodima paper is coming in the mail this next week, and I can start off with my contact frame, but I'd love to get up and running with this vacuum frame ASAP, since so many people have recommended it instead of a printing frame due to inconsistent points of contact/insufficient contact, etc....

thanks!

-Dan

[nolindan]

For 8x10 negatives a vacuum frame is real overkill. You will not notice any improvement in your prints.

However, as wretched excess is so often the name of the game...

A Gast pump is the correct type to get.

You don't really need a vacuum gauge but one will usually come with the frame, along with a bleeder valve. The vacuum gauge will tell you when the frame is evacuated and alert you if there is an air leak in the system or if the bead on the blanket isn't sealing against the glass.

Normally you wait some time after you have achieved vacuum for the air to diffuse out from the materials in the frame. If you are printing against paper this won't be any sort of an issue.

The bleeder valve isn't there to adjust 'pressure' - it is there to bleed off the vacuum so you can open the vacuum frame.

You always run the frame at full vacuum. The purpose of vacuum is two fold: to eliminate any air pockets between the materials; and to use atmospheric pressure to clamp the materials together. Anything less than full vacuum defeats both these functions.

[Drew Wiley]

Vac pumps which work on a piston or flexing diaphragm principle cause micro-surges in air pressure. For critical work this can affect sharpness. Just view the jumpy image in a grain magnifier if you doubt this. It's better to use something which has a fairly constant draw like a small vacuum cleaner. But unless the vac is equipped with variable power, you will need to install a bleeder valve to prevent excess vac pressure. Also beware of where the exhaust air is vented unless you
want dust stirred up, or unless you can afford a true HEPA vac (beware of false
labeling in this respect - they don't come cheap). You don't need much to keep film or paper flat. Even a cordless vac is generally enough, though this option is not ideal because you will be draining batteries quickly and have to repurchase them frequently.

[Drew Wiley]

Nolidan - depends how much enlargement and how flat the paper stays. I ALWAYS
use a vaccum easel for anything larger than 16X20 from 8x10 film and can easily detect the difference, especially in the corners. Sometimes paper or film buckles
during the exposure itself, so merely stopping the lens down further is not the cure.

[Drew Wiley]

Missed one point, sorry .. Yes, the Gast is a rotary vane rather than piston-type, so
if functional should be suitable. I always keep some vac applied during exposure,
and would recommend doing this unless your easel in fact tests out to hold vacuum
just with initial draw. Some papers are a lot more squirrely than others. Film is
generally easier to keep flat. Depends on the design of the easel too.

[Drew Wiley]

And yes, I was referring to enlargement (you can enlarge right onto the stuff with a
strong enough light source and a fast lens), but the same applies to a blanket vs
top glass for contact. Doen't seem to take much vac pressure, but more importantly,
HOW the air exits so nothing gets wrinkled and no pockets remain. Go to a graphics
site like Olec-Stoesser or Ternes Burton to see how the prepress industry designs
their own vac easels, which need to be precisely repeatable between exposures.

[Dan Schmidt]

the diaphragm pump (last link) will be quieter than the rotary vane ones

[Jim Michael]

You might also check industrial suppliers like McMaster-Carr or Grainger.

[nolindan]

Nolidan - depends how much enlargement and how flat the paper stays.

The name's Nicholas Lindan.

The OP is asking about a vacuum frame - a device used for contacting - not a vacuum easel.

My firm designed the nuVac instant drawdown vacuum easel system for nuArc. We have been designing equipment for the pre-press industry since 1979.

The correct type of pump is, as you mentioned, a Gast rotary vane pump, and not a diaphragm pump. However, in contacting there is no air flow when the frame is pumped down and so there is no vibration except that which may be carried by the air hose.

You do indeed need a real vacuum in a vacuum frame.

[Daniel Stone]

hey guys!

thanks for all the info so far, I guess its been my stroke of luck this evening !

literally "just" after I posted this thread, I happened to find a Nuarc vacuum frame on my local LA craigslist(one I didn't notice during my daily searches the past 3wks straight ). Well, I was kind of taken back, the stated outside dimensions in the listing was 26"x30", so it was much bigger than I'll ever need, so I'm still on the lookout for a smaller unit(16x20 or smaller)

good news though: it came with a pump(Gast), had to replace the hose($5 at Home Depot for a 10ft section), the whole unit needed some cleaning up(glass is fine however, nice and clean!), but since I use the facilities at a local photo center, its too big to fit straight onto the table tops in the individual darkrooms . Guess for the time being I'll have to build a raised platform for it so it clears the compressed air outlet sticking out the wall)

the pump takes about 10-15 sec to achieve full vacuum, but the blanket is free of any holes or cracks, and is in pretty good condition it seems.

here's some pictures of my new acquisition

http://i788.photobucket.com/albums/y...ne/frame_1.jpg
http://i788.photobucket.com/albums/y...ne/frame_2.jpg
pulling full pressure
http://i788.photobucket.com/albums/y...ne/frame_3.jpg
blanket sucked tight
http://i788.photobucket.com/albums/y...one/pump_1.jpg
http://i788.photobucket.com/albums/y...one/pump_2.jpg
http://i788.photobucket.com/albums/y...one/pump_3.jpg

-Dan