Electronics > Mechanical & Automation Engineering

Putting vacuums in series (pneumatics)

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TimFox:
With the vacuum you can achieve, there should be a measurable absolute pressure inside, and your sliding seals will leak.  It will be hard to interpret the experimental results.

Capernicus:
I bet it'll be air tight,  I trust my anycubic photon,  but I spose, I haven't actually done it before, I'm just guessing itll be air tight.

The vacuum will be near 0% if its air tight, solid against solid,  except that little bit at the end, where the noddies meet, otherwise it wouldnt be air-tight, I think.

I could add a softbody membrane to it to be sure... let me think, maybe...

Capernicus:
Ive got an easier one, made out of odds and ends around the house.

Itll only evacuate the kebab sticks diametre tho,  so maybe u stuff 3 or so in, depending on the radius of the straw?

Then once uve stuck it in,  you put some tacky on the end, and then u should have the vacuum prepared.

--- Quote from: Capernicus on July 06, 2021, 11:32:40 pm ---I bet it'll be air tight,  I trust my anycubic photon,  but I spose, I haven't actually done it before, I'm just guessing itll be air tight.

The vacuum will be near 0% if its air tight, solid against solid,  except that little bit at the end, where the noddies meet, otherwise it wouldnt be air-tight, I think.

I could add a softbody membrane to it to be sure... let me think, maybe...

--- End quote ---

just do the math, force = pressure * area,  pressure * volume = constant (for constant temperature)

T3sl4co1l:
Pulling on a vacuum costs zero work.  Pushing against the atmosphere however requires work.

The force, of which, is defined by the rate of volume change.  For a piston in linear motion, the cross section is constant, and volume proportional to displacement.

So the force is constant.

This can be a good way to make constant force springs; though it depends on atmospheric pressure (so, varies with altitude).  It's more common to do it with compressed gas ("gas spring"), the pressure of which will increase some with compression, which itself can be a valuable feature (if the minimum volume is zero, then force increases hyperbolically with displacement, making a softer stop than a hard piece of metal, or a rubber bumper).

I don't know what you mean by vacuum vessels "in series".  You can connect them in parallel, joined with a pipe; this simply increases the total volume and equalizes the pressure between them.  Surrounding a rigid vessel in any other pressure (greater or lesser than what's inside) has very little effect, because of its rigidness (small change in volume for large change in pressure).  The situation is different for, say, a balloon (volume varies with pressure differential, in a nonlinear manner), or a bellows or other very flexible structure.  (High altitude balloons are usually little more than loose polyethylene bags; the gas expands at high altitude (lower pressure), eventually inflating the bag to full.)

Tim