Sciencemadness Discussion Board - Constructing a vacuum chamber

Constructing a vacuum chamber

Upsilon - 21-9-2015 at 11:23

Disclaimer: This project is a significant and expensive undertaking. At this point in time this is merely speculation, and this plan is nowhere near ready for execution.

I am thinking of ways to construct a fairly large vacuum chamber that can also double as an inert gas environment. While the chamber is filled with inert gas, I would like to be able to interact with its contents whilst still maintaining a sealed environment from the outside. This is typically done with inverted gloves connected to the chamber. My problem is keeping these gloves from being destroyed while the chamber is in vacuum state.

Essentially I would pull all of the air out of the chamber, and then let the inert gas in. I feel that this is much more efficient and effective than the usual method of simply flooding the chamber with the inert gas until all air has been displaced. Like I said, however, is keeping the inverted gloves from being sucked into the chamber while the vacuum is being pulled.

For the chamber itself, I am considering a 1'x1'x1' cube. I realize this is a poor design for a vacuum chamber, but forming steel into a ball or even a cylinder is too difficult to do in a typical garage. This means that each face of the cube must support over 2000 pounds of pressure, but with 1/4" thick steel plates reinforced with a frame of 1" square solid steel bars will have no issue with these loads (obviously welded togerher; this design may even allow me to enlarge my design beyond a cubic foot). It will be inlayed with PTFE sheets to protect the steel from corrosion due to the presence of certain chemicals inside. Connections would include a connection to the vacuum pump, a connection from a gas cylinder to allow gases in, and electrical outlets to plug in equipment. I will also obviously need a removable lid that can effectively seal when a vacuum is pulled.

The most challenging aspect, I believe, is going to be integrating the inverted gloves into the design. I'm not even sure if it's plausible. If I were to design it, though, it would obviously need to be multiple layered gloves. Perhaps some high-strength glove on the outside like a welding glove to withstand the force pushing it into the chamber. Inside would be a rubber or PVC glove to make it airtight. These would be bolted to the outside of a hole I would cut in the side of the chamber.

I would not even hope to use these gloves while the chamber is under a vacuum, since they will be so stiffly inflated that I would barely be able to maneuver them. However it is a practical option when the chamber is repressurized with a different gas.

Like I said, this is just a rough plan, and I won't even consider beginning construction until at least a few months from now. Any suggestions will be appreciated.

aga - 21-9-2015 at 11:45

Make it small.

Make it Sealed.

Make little robots to do the dirty inside the box.

Edit:

I had an idea to make a small robotic lab, remote controlled, when i first toyed with the notion of doing any EM stuff after joining this site.

Chose to not do any EM at all as i'd have to and physically get the Products by hand.

What the hell. You only live once, and there's no fun in dying intact.

[Edited on 21-9-2015 by aga]

gdflp - 21-9-2015 at 11:46

What kind of vacuum are you hoping to be able to pull with this chamber? 20mm, 1mm, 0.1mm? If you are planning on using 1/4" thick steel for most of the construction, which is quite thick!, what lid material are you planning to use that will be able to withstand an equivalent amount of pressure?
If you just want an inert atmosphere, pulling a 20mm vacuum then backfilling with inert gas two to three times will essentially remove all air from the apparatus, drawing a stonger vacuum is unnecessary. I would recommend seeing if you can have a removable panel with glove holes or no glove holes, similar to the lid, if you are hoping to pull a hefty vacuum as I agree that having gloves present will be a nuisance.

MrHomeScientist - 21-9-2015 at 13:10

You could have a closure system for the glove ports. Let's see if I can describe this well enough. For each glove port, there would be a disk of steel with tabs around the outside rim and a handle on one face. The tabs could be made by slicing segments out of the edges of a larger disk. The glove port would have a similar set of tabs. The disk would sit inside the box and you'd insert your hand into the glove, pick it up by the handle, bring it up to the inner side of the glove port, and turn to lock it in place, sealing the glove essentially outside the box. Sort of like the closure system used by those containers that 100 packs of CD-R's come in.

Also I assume one side of this box will not be steel, otherwise it would be pretty hard to see what you were doing. This face will also have to withstand the pressure differentials, of course. Since this is really just a small glove box, I'd look at how those are designed.

aga - 21-9-2015 at 13:13

Quote: Originally posted by MrHomeScientist

Let's see if I can describe this well enough.

Nope.

You got to do a Video or at least a Photo these days.

Mere descriptive power no longer works.

Upsilon - 21-9-2015 at 13:52

I'm not particularly aiming for a certain level of vacuum; I'm just going to pull until my vacuum pump can no longer pull. The one I have is old but fairly powerful, I'd have to go dig it up and bring the specifics back to you all. I'll do that a little later.

As for the suggestion to pull a light vacuum, refill with inert gas, release, and repeat a few times, this would work but like I said in the OP I'd rather have as little waste as possible. This way I only need to fill the chamber once and would waste less gas.

Also I forgot to mention how I'm planning on including a window. To do that I'm going to cut a small square out of the top side of the chamber. I would then take a thick piece of Plexiglass larger than the hole and use some sort of epoxy to seal it to the steel panel. I may put a piece of glass on the inner side of the window to protect the Plexiglass from corrosive material, but this would not bear any loads.

I'm not entirely sure what I want to do for a door yet. Most likely it will be the majority of one side of the chamber with hinges, sealed with, well, I don't really know what it's called but its that stuff they seal refrigerator doors with. As the vacuum is pulled, the pressure should push it down to increase the strength of the seal.

MrHomeScientist, I think I understand what you're saying. The tricky part with that will be trying to open the little door with the gloves in the way, but it shouldn't be too hard to figure out.

If I were to change the size of the box, I would probably just extend its length to 18". I think this is fairly reasonable; I don't see a problem with it withstanding the extra load.

j_sum1 - 21-9-2015 at 14:01

IIRC, danvizine designed, constructed and posted details of a vac chamber. You should look it up.

aga - 21-9-2015 at 14:52

As per the OP, No, you're not.

Not Doing Anything really, just Talking about an idea.

Do Something, even if it's just a plastic bottle with a syringe attached to make a partial vacuum. Suck hard on a bit of pipe if you need to.

Thinking is Good.

Thinking and Doing is how we (as a species) Discover stuff.

It's also much more Entertaining than mere speculation.

I like the bit where the legs fall off best.

Oh ! We have not gotten to that bit yet. Appologies.

WGTR - 21-9-2015 at 16:45

This is what you're talking about. You just don't realize it yet:

https://www.youtube.com/watch?v=HxX0QUjn_Gk&feature=yout...

http://www.mtixtl.com/desktopstainlesssteelvacuumglovebox24x...

They even have dimensioned drawings on their page. Have fun!

Upsilon - 21-9-2015 at 17:20

Wait a second, are they actually using those puny latex gloves in the chamber while it is under vacuum? I don't believe that; the gloves should inflate like crazy until they explode.

Upsilon - 21-9-2015 at 19:26

Just dug up the old vacuum pump. It's a 5 CFM.

gdflp - 21-9-2015 at 19:59

Quote: Originally posted by Upsilon

Just dug up the old vacuum pump. It's a 5 CFM.

That has nothing to do with the absolute pressure that the pump can pull. It simply indicates the airflow of the pump at atmospheric pressure. The pump should indicate the maximum(technically minimum) pressure that it is capable of achieving, typically the unit will be torr or mmHg, but it may also be psi.

Upsilon - 21-9-2015 at 21:36

That was the only information that the pump had written on it. I guess I'll be looking up the model number.

Oscilllator - 21-9-2015 at 22:34

Upsilon you are way overthinking this. Buy a pressure cooker or similar and follow a tutorial like this one, and you should be able to get one without to much effort. 1/4" steel plates is way overkill, no to mention the potential issues with making airtight welds.
Making a glovebox will be much more difficult. I would suggest making the above chamber first, then considering this option once you have some experience and know what you're getting into.

Fulmen - 21-9-2015 at 22:53

Upsilon: If you study those chambers WTGR brought up you'll see that they are equipped with pressure equalizing lids for the gloves. So they aren't meant for use while evacuated.

One wild idea: If the content/sample isn't fragile, easily disturbed or with sharp edges you could simply use a large inflatable balloon to flush out the air.

Magpie - 22-9-2015 at 08:48

If you just want an inert atmosphere in which to work you don't need to pull a vacuum. Your work space can be as simple as an inflatable clear plastic bag. Craft shops even sell such for this kind of work.

macckone - 22-9-2015 at 11:33

The inert atmosphere in industry is usually done by flushing with a large quantity of
inert gas and then recirculating through an oxygen remover (usually micro ground
iron particles and salt). This mix is available as hand warmers in most places. I think
you will spend more on the vacuum chamber than the inert gas and scrubber. Of
course that assumes your reaction is not nitrogen sensitive and what your oxygen
tolerance is. Cylinders of nitrogen are really inexpensive for rental. Argon cost
more for the gas. If CO₂ is an acceptable gas then it gets even cheaper
and you don't need a cylinder but you do need a drier tube.

phlogiston - 22-9-2015 at 13:02

I don't know how large your hands are, but a 1 foot cube seems like an awfully small space to work in with both hands. I expect it will be impractical to do much.

The size of your box is entirely restricted by your requirement of being able to pull it vacuum, but you never intend to work with the gloves in a vacuum. Therefore, I think it makes more sense to make a largeish glovebox for inert atmosphere work, that you can work in comfortably and a separate, smaller vacuum chamber with no gloves.

View it from a pragmatic perspective.
While a nice challenge, you should consider the possibility that the money you spend on realising the design you are now planning will buy you a lot of inert gas, possibly more than you will ever save by having the ability to do the vacuum/gas cycles. And that is not counting your time (You could spend the time building this delivering pizza's and buy the gas). Especially if you eventually find the cramped space so impractical that you will eventually hardly ever use the box, it would be a dissappointing waste of your time and money.

That being said, if you decide to pursue this further, why build a square box using lots of steel if you can use a discarded fire extinguisher or other source of pipe which is a much more optimal shape? You will only need to worry about the end caps then.

For gloves, check out what NASA uses for their spacesuits.

[Edited on 22-9-2015 by phlogiston]

Twospoons - 22-9-2015 at 14:29

The other starting point for your chamber could be an empty propane or LPG cylinder. They come in many sizes, and are relatively cheap. Just be sure to flush out any residual gas if using a second hand one - you don't want a spark igniting anything when cutting into the cylinder. The usual method is to fill the cylinder with sand.
I rather like the pressure cooker idea - its almost ready to go.

Dr.Bob - 24-9-2015 at 17:59

Magpie is right, the simple answer is to just use a disposable type glove bag. You can suck a vacuum on one, then inflate it and have a decent air-free space which is somewhat easy to work in. I have used one before for working with potassium hydride in a humid area, and it worked well. I have also worked in a real glove box, and those are not easy to work in at all, but do work well.

They are great to use, but even they have issues, if you use more than one chemical at a time, the vapors of them can mix in the inert gas system and make a mess (think HCl and TEA for example). So while it seems great to be able to uncap butyl lithium and just pour it without care, in reality, you have to still handle it with a syringe and needle still. But a glove bag can allow you to make air-sensitive metal complexes, handle strong bases, work with pyrophorics, and use sensitive catalysts with less trouble. But you have to be careful as when you unassemble your glove bag/box, the remaining compounds have a tendency to still catch fire or still be toxic, so best to work inside a hood or outdoors.

Upsilon - 24-9-2015 at 18:28

The glove bag is an appealing idea, but it seems like it would be difficult to pull a good vacuum over some flask, for example. I feel like the bag would seal over the mouth of the flask and prevent the air in the flask from being sucked out.

That, and if you accidentally start generating a lot of gas somehow, it'll probably pop. Or, if you're intentionally generating gas with electrolysis. That's another thing, it doesn't seem like a good idea to use a bag to melt NaOH in.

Upsilon - 31-10-2015 at 13:15

Alright, so after much thinking I have decided against the steel cube design I was considering. It seems like a big headache to me. I have no experience with steelworking so I doubt I could make a very good box on the first go. Not to mention it's expensive.

So, I am now thinking of a more modest design, made from a 1' length of 6" diameter schedule 40 PVC pipe. This is supposed to have a 5/8" thick wall so I think it will be perfectly fine holding a vacuum. The problem is, I still want to be able to heat substances inside of the chamber. PVC pipe has a max temperature of about 140C. While I won't really be melting anything at very high temperatures, I would still like to achieve around 300C if possible. I think this is doable with insulation - the PVC pipe would be the outer layer, with a healthy layer of insulation inside, and finally an aluminum foil innermost layer.

The biggest problem I see is the heat transfer from an outside source of heat. I would need to use a steel disk to seal the end of the pipe that I'll be heating from. Which means I would need insulation between the steel disk and the PVC pipe's circumference. Doing that compromises the airtight seal. I would need some kind of high-temperature seal to coat on the outside of this insulation ring to keep it airtight.

First, what kind of insulation material would be best for this? And does anyone have an idea for a high-temperature sealant?

careysub - 31-10-2015 at 14:57

Quote: Originally posted by Upsilon

Alright, so after much thinking I have decided against the steel cube design I was considering. It seems like a big headache to me. I have no experience with steelworking so I doubt I could make a very good box on the first go. Not to mention it's expensive.

So, I am now thinking of a more modest design, made from a 1' length of 6" diameter schedule 40 PVC pipe. This is supposed to have a 5/8" thick wall so I think it will be perfectly fine holding a vacuum. The problem is, I still want to be able to heat substances inside of the chamber. PVC pipe has a max temperature of about 140C. While I won't really be melting anything at very high temperatures, I would still like to achieve around 300C if possible. I think this is doable with insulation - the PVC pipe would be the outer layer, with a healthy layer of insulation inside, and finally an aluminum foil innermost layer.

The biggest problem I see is the heat transfer from an outside source of heat. I would need to use a steel disk to seal the end of the pipe that I'll be heating from. Which means I would need insulation between the steel disk and the PVC pipe's circumference. Doing that compromises the airtight seal. I would need some kind of high-temperature seal to coat on the outside of this insulation ring to keep it airtight.

First, what kind of insulation material would be best for this? And does anyone have an idea for a high-temperature sealant?

What advantage does this have over a old pressure cooker?

If you making a PVC chamber you should be looking at doing the heating inside the chamber with some kind of resistive heater. Then a PVC cap, with a gasket could be used to close.

Fiberglass batts are probably the best insulation.

Upsilon - 31-10-2015 at 15:35

Quote: Originally posted by careysub

Well, a pressure cooker is designed to contain high pressures, not a vacuum, so I don't know how well it would work. They operate at about twice atmospheric pressure, and the structure is more efficient at containing a high pressure rather than a low one. Pulling a vacuum in it would be putting it against its normal operating pressure but from the outside instead of inside. That, and I don't have a pressure cooker, and I want to be able to easily cut a window and other holes, and also because I feel like the aluminum would corrode much faster than PVC against certain substances. Granted, the aluminum foil in the PVC design will also corrode, but this can be cheaply replaced. The pressure cooker may work perfectly, but I think the PVC pipe is a more feasible option in my situation.

Also, the heating element inside of the chamber sounds like a good idea, but I wasn't completely sure if I'd be able to fit something in there. Remember, the pipe only has a 6" inner diameter, and after insulation I may only have 4" of space. Still, it seems like a better idea than trying to seal a steel plate to the pipe. This will also help the heater to be extremely efficient; no loss by convection, and much of the radiation can be reflected back by the foil. Hell, I could probably get away without even insulating the PVC since it will absorb very little heat this way. But I also want this to function as an inert gas chamber so I'll have to insulate it anyway.

careysub - 31-10-2015 at 16:01

Try looking at Goodwill for a pressure cooker, any you find there will be aluminum. I see a new 6 Qt aluminum on eBay for $19 including shipping. You don't need a premium model for this.

Holes can be put into aluminum with a hole saw, it drill and taps with ease. You would need a good gasket of course (if buying used). Silicone gaskets should take pretty high temperature.

Pressure cookers do hold vacuum - after you have finished canning or cooking and the cooker has cooled you have to break vacuum before you can open it. You will be attaching this to a pump so small leakage (if any exists) will be taken out by the pump.

Also consider buying a battle-scarred All American pressure cooker on eBay or Craig's List. These are the Cadillacs of pressure cookers, are large (for canning) 10-20 qt and use an aluminum metal-to-metal seal (no gaskets). Options exist for under $100.

I wonder if a wide angle peep hole viewer could be installed in a tapped hole for viewing, with a small incandescent bulb installed inside.

[Edited on 1-11-2015 by careysub]

Upsilon - 31-10-2015 at 16:34

You know, I may just try out the pressure cooker after all. I don't think it would be too difficult to layer the aluminum with some form of protection from corrosion. It would also be much more spacious than a PVC pipe. I see a nice for-parts one on the Goodwill website, shipped to my door for $7; I really can't refuse that. I'll see what I can do with it.

Also, I'm not sure that the vacuum you describe is a very strong vacuum - it is only caused by the contraction of the gas inside the cooker upon cooling. Some calculations would probably reveal how strong of a vacuum it is, but I don't really feel like doing them.

EDIT: I misread, shipping is actually $15. Still, might be worth a shot.

[Edited on 1-11-2015 by Upsilon]

careysub - 31-10-2015 at 18:51

If you cool the pot to 45 C before opening you are pulling 90% vacuum, a perfect vacuum would not contribute appreciably more force.

Upsilon - 31-10-2015 at 19:52

Out of curiosity, could wood be used as an insulator in a vacuum? Since there is no oxygen for it to combust with, what happens to it when it gets hot, and what temperature does this occur at?

careysub - 1-11-2015 at 06:28

To start off with out-gassing while trying to bring down the vacuum could be a nuisance.

Wood will pyrolyze at a high enough temperature (starting at 200 C) even in an inert atmosphere or vacuum (releasing more gases), and suppose the inner surface of the wood gets really hot - and then your break the vacuum to end the experiment?

Instant combustion is a real possibility.

There are good non-combustible insulators readily available: fiberglass, loose perlite, cermaic suppliers have a variety of suitable products. I have Kaowool from Seattle Pottery. for example. I see Thermwell As5 Cermic Fiber for $11 on Amazon.

Upsilon - 1-11-2015 at 08:19

Ok. I wasn't actually planning on using wood as an insulator, I was just curious about what happens to it when it gets hot without oxygen.

Upsilon - 5-11-2015 at 18:47

Alright I decided to go for the PVC pipe chamber just for better customization and workability. I have already gotten a 1 foot long section of 6 inch diameter schedule 40 PVC pipe. Wall is 5/16 of an inch thick. Internal pressure rating is 180 PSI so I think it should work just fine for holding a vacuum. I also got a small 1/4 inch thick polycarbonate window. Once I get end pieces for the pipe (one end will just be a cap cemented on wile the other will have a screw cap fitting). I'll cut a hole out of the screw cap to place the polycarbonate window over.

For including a heating element, I have decided to use induction hearing - the only apparatus inside the chamber would be a steel disk. The induction coils will be around the outside of the chamber.

After this I'll need to add some fiberglass insulation sandwiched between the inner wall of the pipe and a layer of aluminum foil. Being in a vacuum, the pipe should remain well below its decomposition temperature with the aluminum foil deflecting radiation away from the walls. The fiberglass is just for added protection. This will also make the heater very very efficient.

Later on I may add onto the design. Something I'll likely do in the future is have some electrode ports for conducting sensitive electrolysis experiments, e.g. sodium from sodium hydroxide. I don't think I'll be giving it inert gas capabilities, especially since having a gas inside the chamber risks heating the PVC too much.

Upsilon - 6-11-2015 at 17:31

So, uh, I've got an issue - I can't find any PVC caps that fit the pipe I bought. The pipe has a 6.625" (6 5/8") outer diameter and a 6" inner diameter. I went to the local home improvement store and all of their caps were only a 6" inner diameter when I need a 6.625" inner diameter. I can't find squat online either - any help here?

Magpie - 6-11-2015 at 17:42

What you have is 6" schedule 40 PVC pipe. A 6" pipe cap should fit that. Home Depot claims to have 6" schedule 40 PVC pipe caps: http://www.homedepot.com/s/6%2522%2520PVC%2520pipe%2520caps?...

Upsilon - 6-11-2015 at 17:49

Quote: Originally posted by Magpie

What you have is 6" schedule 40 PVC pipe. A 6" pipe cap should fit that. Home Depot claims to have 6" schedule 40 PVC pipe caps: http://www.homedepot.com/s/6%2522%2520PVC%2520pipe%2520caps?...

Unfortunately it doesn't seem to be that simple. I was at Lowes and they had this there:
http://m.lowes.com/pd/Charlotte-Pipe-6-in-dia-PVC-Cap-Fittin...

However for some stupid reason these caps seem to be 6" inner diameter instead of fitting 6" schedule 40 pipe. Maybe they had the wrong thing in the store - I may try Home Depot next.

[Edited on 7-11-2015 by Upsilon]

Magpie - 6-11-2015 at 18:02

That cap is for DWV (drain/waste/vent) and as such may have a smaller ID for the thinner wall pipe than for schedule 40 which is a pressure pipe size.

careysub - 6-11-2015 at 18:38

Quote: Originally posted by Upsilon

After this I'll need to add some fiberglass insulation sandwiched between the inner wall of the pipe and a layer of aluminum foil. Being in a vacuum, the pipe should remain well below its decomposition temperature with the aluminum foil deflecting radiation away from the walls. The fiberglass is just for added protection. This will also make the heater very very efficient.

How hard do you expect the vacuum to be?

The reduced pressure may be less effective as insulation than you think.

People are always surprised to learn that vacuums do not reduce heat conduction through gases *unless* the pressure is so low that the mean free path is larger than the dimensions of the space across which the heat is being transported. (I agree it is surprising - the reason for it is that although fewer molecules are hitting a surface, they carry heat farther, so that it balances exactly.) The ratio of the MFP to the distance scale is called the Knudsen number, when Kn > 1 the low pressure gas acts as an insulator.

Since the MFP at STP is 66 nm this means the pressure must be 0.005 torr to increase the MFP to 1 cm. At 1 torr (5 micron MFP) fiberglass insulation is improved in it insulation value by about 1/3 over atmospheric, which is something - but not a lot. You get the same improvement (1/3) by replacing the air with argon or CO2. To get a really substantial improvement you need to go down to <0.1 torr.

You best bet is pack the chamber with fiberglass insulation pretty tightly - this suppresses convection, reduces the MFP in the insulation, and makes the insulation opaque to radiation conduction (glass is opaque to thermal radiation). A final foil layer against the PVC is a good idea.

Upsilon - 6-11-2015 at 20:09

Quote: Originally posted by careysub

That'll definitely be something to test once I get it built. I have an old 5 CFM 2-stage vacuum pump (an equivalent modern unit seems to be ~$200) so it should pull a decent vacuum, but I won't know for sure until I test it.

EDIT: These new equivalent models seem to claim ability to achieve 0.3 Pascals which is an insanely strong vacuum.

[Edited on 7-11-2015 by Upsilon]

annaandherdad - 6-11-2015 at 22:24

Quote: Originally posted by careysub

People are always surprised to learn that vacuums do not reduce heat conduction through gases *unless* the pressure is so low that the mean free path is larger than the dimensions of the space across which the heat is being transported. (I agree it is surprising - the reason for it is that although fewer molecules are hitting a surface, they carry heat farther, so that it balances exactly.) The ratio of the MFP to the distance scale is called the Knudsen number, when Kn > 1 the low pressure gas acts as an insulator.

Since the MFP at STP is 66 nm this means the pressure must be 0.005 torr to increase the MFP to 1 cm. At 1 torr (5 micron MFP) fiberglass insulation is improved in it insulation value by about 1/3 over atmospheric, which is something - but not a lot. You get the same improvement (1/3) by replacing the air with argon or CO2. To get a really substantial improvement you need to go down to <0.1 torr.

I'm impressed by your knowledge. The old thermos bottles you used to be able to buy, they were glass with vacuum and silvered to cut down on the radiation...sounds like you're saying they must have had a really good vacuum, about .01 torr. All I ever knew was that they were easy to break.

careysub - 6-11-2015 at 22:36

Quote: Originally posted by annaandherdad

Quote: Originally posted by careysub

Thanks.

Yep. They had really good vacuums, about 0.001 torr in fact.

And, yes, they were easy to break, I remember getting to school in the wintertime as a child and having my heart sink when I heard my thermos of hot cocoa going "slush-slush" when you moved it.

Kn > 1 is also a necessary condition for Crookes radiometers to work (those black and white spinning vanes in a glass bulb). The force that spins them is the black vane surfaces getting warm, and the molecules bouncing off them getting "hot" (gaining kinetic energy and momentum) and depositing that energy on the enclosing bulb. Molecules bouncing off the white sides are cooler, slower, and thus a net torque is generated. If the MFPs were smaller then the fast molecules would collide with other molecules, and the momentum would be redistributed and end up being redeposited on the vane surface, cancelling out the original force.

[Edited on 7-11-2015 by careysub]

Upsilon - 7-11-2015 at 09:43

Home Depot was even worse than Lowes. Looks like I'll have to be ordering the stuff online and hoping it fits.

Magpie - 7-11-2015 at 10:38

Do you have an industrial supply business in your community? There's not much need for 6" pressure piping in residential projects.

careysub - 7-11-2015 at 10:59

See if any companies specialize in sewer line installation in your area. They can be sources for larger sizes. Fitting should not be a problem if the part is available since the sizes are standard.

I have ordered hard to get pipe fitting from Zoro Tools, with good success:

http://www.zoro.com/lasco-cap-6-in-slip-447060/i/G5275243/

Upsilon - 7-11-2015 at 11:32

I am actually looking at their inventory currently. So, I think the cap will fit. Now I also need a screw cap for the top end of the chamber. I imagine something like this should fit as well?
http://www.zoro.com/genova-cleanout-body-pvc-6-in-41659/i/G6...

EDIT: Ok so these won't work after all - their standard is ASTM D3034 which is for sewer lines. The pipe I have is ASTM D1785.

[Edited on 7-11-2015 by Upsilon]

zed - 7-11-2015 at 12:46

Stainless steel pressure cookers abound at my Portland Goodwill stores. Usually, about 10 to 20 dollars, when they have 'em. The so called, "Superstore" on SE 6th might be the best place to look.

The sides are round, and the tops are slightly domed. Making the flat bottom the weakest link. One with an Aluminum clad bottom, might be somewhat stronger.

Should be strong enough, to not cave-in under vacuum. But, as always, such things remain to be seen. You'll find out.

Upsilon - 7-11-2015 at 16:44

Quote: Originally posted by zed

Stainless steel pressure cookers abound at my Portland Goodwill stores. Usually, about 10 to 20 dollars, when they have 'em. The so called, "Superstore" on SE 6th might be the best place to look.

The sides are round, and the tops are slightly domed. Making the flat bottom the weakest link. One with an Aluminum clad bottom, might be somewhat stronger.

Should be strong enough, to not cave-in under vacuum. But, as always, such things remain to be seen. You'll find out.

It just seemed like a hassle to try and deal with a pressure cooker, since they have 2 layers of metal with a heating element in between. Regardless it's too late now, I've already invested into the PVC design.

Upsilon - 8-11-2015 at 08:40

Ok, so I have definitely found caps that will work. However, the screw cap isn't going to happen - it costs way too much. Therefore I need some kind of strong ring to put over the other end of the pipe. It would need at least a 6 5/8" outer diameter and around a 5" inner diameter. This would be cemented to the rim of the pipe. Over the hole in this ring, I would place the polycarbonate window. On the window I would use something like a refrigerator door seal so that when the vacuum is pulled, the window will be held fast to the ring.

Magpie - 8-11-2015 at 09:05

If the open end of the pipe is perfectly flat you can likely just use a flat piece of plywood, metal, plastic or glass of sufficient thickness. Buy a small piece of rubber (say EPDM) and silicone glue it the plate. The vacuum should hold it in place with virtually no leakage. This method is used for bell jars that hold vacuum.

I have bought 1/16" and 1/8" EPDM cut to size at a rubber suppliers.

zed - 8-11-2015 at 14:23

"It just seemed like a hassle to try and deal with a pressure cooker, since they have 2 layers of metal with a heating element in between. Regardless it's too late now, I've already invested into the PVC design."

We are envisioning different machines. Hereabouts your average pressure cooker is a simple, long handled, heavy gauge, metal pot, with a gasketed lid. Doesn't have double walls, or anything like it. Doesn't have internal heating elements.

[Edited on 8-11-2015 by zed]

Upsilon - 8-11-2015 at 17:07

Quote: Originally posted by zed

"It just seemed like a hassle to try and deal with a pressure cooker, since they have 2 layers of metal with a heating element in between. Regardless it's too late now, I've already invested into the PVC design."

We are envisioning different machines. Hereabouts your average pressure cooker is a simple, long handled, heavy gauge, metal pot, with a gasketed lid. Doesn't have double walls, or anything like it. Doesn't have internal heating elements.

[Edited on 8-11-2015 by zed]

Well, regardless I've already started with the PVC project so I'm bound to stick to it. I've ordered a 1/8" thick 8" steel disk that I'll need to cut a hole out of. This relatively small thickness should be cuttable with a propane torch.

Upsilon - 12-11-2015 at 15:19

Got the cap in the mail today and it fits perfectly. I also should have gotten the steel disk today, but USPS mail people are lazy as crap. It wouldn't fit in the mailbox so they just put in a "Sorry we missed you!" slip in the mailbox, saying that it "requires a signature" (for a $5 piece of steel??). Definitely a load of BS since nobody ever rang the doorbell.