Typical vacuum/pressure in a domestic vacuum/Thermos flask

[Mr-Pooman]

I am trying to replicate a vacuum flask (on a low budget) with a 1m long 8 inch UPVC pipe forming the outer shell. A search of the internet suggests that the influence of convection stops around 10 Pa, however the vacuum pump I have, a two stage rotary 3 cfm advertised to achieve a vacuum of 2 PA, can only achieve around 350 Pa. My question is, what is the typical vacuum/pressure in a domestic vacuum/Thermos flask and how is it achieved? i.e. a vacuum pump or creating a void in the manufacturing process.

 

[LittleInch]

https://www.eng-tips.com/viewthread.cfm?qid=212672

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

When we made them in the lab we always used 10E-5 Torr (1mPa) as an upper limit.
For large bulk storage tanks the limit is not as low, I recall using 0.05mbar (5Pa, ~40mTorr).
There also contain multilayer aluminized mylar foil in the vacuum space to reduce heat transfer.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Mr-Pooman]

Thanks LittleInch and EdStainless, I'll just have to find a better pump. One thing EdStainless what volume do you consider to be bulk storage and why do you think this to be the case.

 

[EdStainless]

Thousands of liters is bulk storage, you know tanks that are 20' tall and larger.
It is twofold, there are limits on what is practical with that size installed outdoors, and they make up much of the difference with the layered aluminized mylar film.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed