evil_lurker
National Hazard
Posts: 767
Registered: 12-3-2005
Location: United States of Elbonia
Member Is Offline
Mood: On the wagon again.
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Idiot proof aspirator design (hopefully)...
After spending most of yesterday afternoon chasing geese and coming up with a bunch of parts that ain't the right size, I think I have finally came up
with a decent vacuum aspirator design.
The main problem with the aspirator designs I have seen (frogfots & tecno tachos) is that they both use copper pipe for the injector and the exit
fitting has to be machined with a 45 degree bit.
In the USA, most copper pipe of the 1/4 inch variety found in hardware stores is of the refrigeration type which is measured by the outside
diameter unlike most other pipe measured which is measured by the inside diameter. The 1/4 inch is more like 5.88mm on the inside rather
than the 6.3mm called for in tecno tacho's design. This bungs up the "critical ratio of maxium performance" and makes it very hard to find other parts
that fit snugly. If you can find the right stuff, then you gotta work it, and that is very difficult because its usually a little bit crooked, very
soft, and hard to hammer down into a cone.
The other problem is with the fittings that have to be drilled. A 45 degree angle bit is very hard to locate, but the 82 degree ones are common and
cheap as dog crap from any hardware store. Of course, according to design this is not optimal.
I think I have figured out a way to manufacture an injector nozzle and exit pipe without copper or machining.
So called "hobby brass" pipes can be found at craft stores. Hobby Lobby in particular is one of them. They are straight, can telescope within each
other, and come in exactly the right size and are cheap. The standard wall thickness is 1/64th of an inch. Like the copper refrigeration line, hobby
brass is also measured by the O.D, but the wall thickness is uniform. So, for the 1/4" exit tube, you would need 9/32" diameter pipe.
Now, instead of drilling the fitting where the pipe exits, you simply get a hose barb fitting big enough snugly hold the brass pipe, and then flare
the end with a 45 degree flaring tool and slip it in with a little epoxy resin to hold it. Hell you don't even have to buy the flaring tool... just go
to any of the larger auto parts store chains and ask to borrow theirs for a minute...
To do your injector tip, first get a tube of caulking and cut off the tip all the way towards the end. Then cut off the very tip leaving a small
hole, and carefully take a drill bit and ream it out till its the right size of about 4mm. Then simply take some glue and slip it on a length of 3/8"
OD hobby brass pipe till its snug. Your done. Instant nozzle.
Anyways, will see how it works out and will posts the results later...
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Rosco Bodine
Banned
Posts: 6370
Registered: 29-9-2004
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Mood: analytical
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A Nalgene aspirator is about as good as they get
and cost under 20 dollars . I have used them for years .
http://vwrlabshop.com/product.asp?pn=0006435&bhcd2=11524...
The check valve won't withstand strong acid vapors ,
but it can be removed and an external all glass or teflon
check valve can be used instead .
I have wished that they would make an even smaller
orifice version in all teflon and having a needle adjustment air bleed for throttling the vacuum .
Anyway using the sizes of tubing which you are describing , you are going to have an enormous water consumption . The water orifice diameter in that
Nalgene
pump is only about 1/16" to 3/32" at most IIRC , and it pulls a lot of vacuum at a good rate .
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12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
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Mood: informative
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If you have a grinder and a keen hand, you can grind your own drill bits. Hell, you should know how to sharpen drills anyway, save yourself some
cash. Anyway, my point is, if you felt like grinding a new point on a drill, you could grind an absurd angle, such as the 45 degrees you mentioned.
Tim
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evil_lurker
National Hazard
Posts: 767
Registered: 12-3-2005
Location: United States of Elbonia
Member Is Offline
Mood: On the wagon again.
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Ah well I'm going to run it off a 1/2 Hp pump on circulating bath...
The pump I'm looking at is:
http://www.northerntool.com/webapp/wcs/stores/servlet/produc...
The specs are:
1/2 HP 110 Volt 2.75 Amp single phase motor
Motor Speed: 3400 RPM
Pump is not self-priming
Maximum Total Head: 110ft.
Maximum Suction Lift: 20ft. with foot valve
1in. suction/discharge ports
Moves up to 720 GPH at 2ft./10 GPM
Max PSI: 55 PSI
Cast iron construction
Cast brass impeller
Not submersible
Price $34.99 plus shipping!
Anyhoos, the prototype aspirator is up and running, however the nozzle will definatly need some fine tuning. It seems that the most important thing is
not so much the diameter of the nozzle or the pitch of the cone, but rather whether or not the nozzle throws a round or flat stream. Straight round
streams seem to kill your efficiancy while if you get one that throws a good flat stream a few inches from the nozzle is perfect.
Hell, now that I get to thinking about it, cynmar has a two stage vacuum pump for under $250... for all the hassle I might just go ahead and get it
and be done with it...
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