Sorry for the delay in response.I'm in werk season .....
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Polymer caps are rated -55c I believe.But that is the standard minimum temp for consumer products....I'm betting cold is no problem , they are all plastic after all.....
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Update time.
I have re-thought a couple of things.I decided the dewar isnt big enough , based on the sizes of the pump I am making.
Therfore , I have purchased a fullsized keg , and 2 foot section of 12" stainless pipe to make a larger dewar.I'll have pics soon.
I feel this step is required based on safety design actually , and here's why ;
The way I am designing this , If the power fails , all the liquid in the main tank (the glass one) needs to drain out , by gravity .The bottom tank where the dry ice is , is safer than the main one from a fire standpoint ,based on the co2 output of the DI.
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I am sizing the first piece of borosilicate glass for order.While I'm making it as thrifty as I can , the glass bill will exceed 700$ , after all is said and done I'm sure....so'k tho , the first 300$ of glass is paid for.
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I am in contact with Dow Corning regarding silicone sealants.They suggest -80c is no problem.
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I have done more thinking regarding the pump.we'll see ....