Progress on vacuum chamber build - helium leak detection, custom flanges----make money online

hey everyone there's a quick update on

my vacuum chamber progress I've lived a

whole bunch of custom parts that I

needed to have to interface to the

fittings on this diffusion pump so we're

looking at the underside of the vacuum

table this is the high vacuum penning

gage and this is the diffusion pump and

this joint here is a universal joint

that's connected to a shack that goes

outside the cabinets that I can open and

close the valve that it's actuated on

the top of the diffusion pump over here

there's another valve and this one also

has a universal coupler that I've

connected a shaft up to yet but what

took me the most amount of time this

weekend is machining some aluminum

fittings here and here to interface this

valve to the diffusion pump so there's a

standard for high vacuum connections

called NW or KF I guess and it's

basically two flat pieces of metal that

are pushed together by this ring so if I

undo this you can open the ring up and

the two pieces come apart so that's

standard however there's connections

that go to the diffusion pump that are

similar but not quite the same it has

these black plastic rings and there's an

o-ring sandwiched between the two pieces

of metal but it's not billed quite the

same way so I had to spend some good

quality time on the lathe and make up

some custom adapters I'm not even really

sure what this thing is called I think

it's maybe an Edwards specific adapter

you can also see I've got a thermocouple

vacuum gauge tacked on to the end there

and that was another custom adaptor that

the gauge is screwed into I just used a

pipe thread on that one this is the

input to the mechanical vacuum pump and

it goes into a tee here and this side

goes up to the first valve that I showed

in the video direct into the chamber and

this side goes through a valve here and

then into the diffusion pump so the way

that this works is that we can switch on

the diffusion pump you know with the

bell jar shut and get a good vacuum in

there and then if we want to change the

specimen inside the bell jar what we can

do is close this valve and close the

other valve and close the valve leading

from the diffusion chamber or the

diffusion pump into the chamber and then

remove the bell jar and

bring that back up to atmosphere and

then by opening this valve first we can

clear the chamber of most of the air and

then open the open the valve going to

the diffusion pump and get the rest of

the air out so this arrangement of

valves lets us bring the chamber up and

down to atmosphere much more quickly

than we would otherwise when I first

pumped down the chamber I could tell

that I had a leak because the pressure

was staying above about a hundred or 150

milli Torr which is really much too high

and I could tell that by closing and

opening valves there actually was either

a very you know a piece of material

outgassing quite a lot or an actual leak

that was dumping air into the chamber so

one way you can test for this is using

helium I've got a helium tank and what

you do is you just spray the helium

around the outside if your vacuum setup

and wherever helium gets into the system

will cause the vacuum gauge to dip the

reason for this is that helium has a

different thermal conductivity than

nitrogen and oxygen do so when the

helium enters the vacuum gauge it causes

it to respond differently than it would

to air even though the pressures might

not actually be all that different

also helium is able to permeate through

many different materials and just get

through very small spaces in general so

it's a good leak detector gas in fact

it's the best I think in this case the

leaks turned out to be bad Oh rings in

the hot section of the diffusion pump so

there's two green o-rings Green probably

indicates Viton and these o-rings are

used to seal the diffusion pump oil into

the bottom of the chamber one's a drain

and one's actually serve a little

dipstick I guess over the years the high

temperatures just destroy that Viton so

luckily I had actual Edwards replacement

o-rings that I bought online so the next

project is to get some feed throughs

going through this plate here and since

the primary purpose of this vacuum

system is going to be a vapor deposition

machine I'm probably going to come up

with something like this so I'm going to

drill a large hole through the plate and

then put this through like this this is

an aluminum boat with a standoff that I

threaded into the top of it I actually

might machine this whole piece out of a

solid

out of a solid piece of aluminum or

other material just so that I don't have

to have another joint in here but anyway

the basic idea is to have something like

this so that inside the chamber I can

put my tungsten or molybdenum heater on

this and that this will allow a large

current to flow through the boat the

heater and evaporate that material I

plan to use soldering guns and deliver

the low-voltage high-current that I'll

need to heat up that tungsten and

Lebanon boat heater and I'll have more

details about this hopefully in the next

video but the amount of cross sectional

area for one of these aluminum

conductors is roughly equivalent to this

bolt that I've got here so I figured

using this I'll be safe and on what I'm

going to do is remove this bolt from the

remove this aluminum conductor from the

gun and just use the transformer to get

down to a few volts at a few hundred

amps so it ends up being or actually

it's not quite that much it's more like

260 watts total so at 1 volt it might be

260 amps or something in that region

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