# Tag Info

5

Start out by doing some basic calculations. Air is mostly N2, with a atomic mass of 28, and O2, with a atomic mass of 32. There is more nitrogen than oxygen, so let's say air has a average atomic mass of 29. At 0 °C and 1 atm, one mole of ideal gas occupies 22.4 liters. Let's say 20 °C is more realistic, so we'll scale that by the absolute ...

5

In the molecular flow region of pressure, the thermal conductivity of an ideal, monatomic gas is obtained by this equation. $$k = \frac{1}{\pi^{3/2} d^2}\sqrt{k_B^3T/m}$$ where $d$ is the collision or molecular diameter and m is the molar mass divided by Avogadro's number. It is independent of pressure. Approximations have been derived for non-monatomic ...

4

I'm assuming that the piece with the groove and the mating pieces are metal or a dense molded plastic. If this was a 3d printed piece, I'd be worried about porosity of the parts too. A second O-ring won't do much for you honestly. If your leak rate is that high, I'd question the design of the O-ring groove and O-ring selection. Does the O-ring sit proud of ...

4

I did some internet searching and did not find anyone that had done a direct swap out. Granted, probably the majority of these replacements occurred before the existence of the internet ;-). As I am sure you are already aware (but to be thorough), modern diffusion pump designs do use synthetic working fluids. It will probably take some fine tuning of the ...

4

You do not need full vacuum to accomplish your goal. A small amount of vacuum pressure adds up really quick over a large surface area. Try to make the entire footprint of your robot under vacuum; your sealing perimeter increases linearly with diameter, but area increases with diameter squared. Basically this means the problem is easier to solve the larger ...

4

Geissler invented the so-called "liquid piston" pump using mercury for the piston. The basic idea of the design is to entrap some of the air between two volumes of mercury in a pipe, and then force the mercury along the pipe to release the air into the atmosphere. Geissler achieved 0.1 Torr with that design of pump in the 1850s. Sprengel invented an ...

4

The equivalent of a capacitor in terms of pneumatics would be a chamber such as a metal sphere the size of a tennis ball. It would be necessary to have an external vacuum pump to evacuate the air prior to the quick release. Auto tire houses use the reverse concept to seat a new tire on the rim. A cylindrical tank is loaded to substantial pressure by a ...

3

Perhaps, depending on the materials, you could try gently heating one piece while cooling (or at least heat-sinking) the other piece, and hoping that the expansion mismatch will separate them. You haven't identified the glass types nor their surface quality-- if the interface areas are porous, your contaminants may well have formed physical bonds which ...

3

An important point in the fluid dynamics design is about control points. A simple experiment - hold your hand over a hose on the vacuum cleaner, you'll notice a light vacuum pulling on it, but hold your hand right on the top of the hose, and it feels like it is pulling significantly harder. This is because fans operate on a load response curve, and when ...

3

The small tube I believe is for the freezer coil, or it could be a capillary tube (thank you Swift). Regardless, simply solder it shut and use the two larger lines for pumping. I would like to note, this style of compressor cycles some of its lubrication through the refrigeration system, so keeping the crankcase full of oil is important since any oil lost ...

3

The simplest way to do this would be to design your own. A commercially available spring, with an OD of 9mm, a length of 19mm, and a wire dia. of 1mm has a rate of 3.15 N/mm, with 11.5 mm compression length. Putting the lowest possible regulator in front of your homemade regulator, set a large diaphragm across a 1m diameter expansion chamber. Then, ...

3

It is unlikely polymers will be an issue, but the additives used may pose problems. Polymers should have negligible volatility due to their long chain nature. Polymer additives may still pose an issue. You may need to test any particular filament material to ensure it meets your needs. Polymer Chain Mobility Polymers do not behave like small molecules in ...

3

I found this formula here: $$p_{crit}=\frac{2\,E\,t}{D}\left(\frac1{(n^2-1)\left(1+\left(\frac{2\,n\,L}{\pi\,D}\right)^2\right)^2}+\frac{t^2}{3(1-\nu^2)D^2}\left(n^2-1+\frac{2\,n^2-1-\nu}{\left(\frac{2\,n\,L}{\pi\,D}\right)^2-1}\right)\right)$$ So you should set $p_{crit}$ to about 3 atm to be safe, then find $E$ and $\nu$ for your aluminum, plug those in ...

3

Different techniques have been developed to evaluate the efficiency of energy use by a vacuum pump. Most vacuum pump manufacturers catalog their test results, including brake horsepower (actual hp) and cfm vs. vacuum level. Fairly accurate evaluations of power needs can be made from such information sources. For example, the relative efficiency of different ...

3

The device you're looking for is called a vacuum regulator and sits between the vacuum source and the process. This page from Equilibar shows some examples and provides links that explain how they work. You can also use a vacuum breaker, which operates more or less like a pressure relief valve, but a vacuum regulator will offer more precise control. There ...

3

The device is called a "receiver" in pneumatics - this is basically the tank you see on any garage compressor, or much larger and more elaborate setups in industrial settings. Its function can be modelled almost exactly like a capacitor. It stores energy by accumulating air inside of it (the integral of the incoming flow, just as charge is the integral of ...

2

I think your confusion is in absolute vs gauge pressure. Atmospheric pressure is about 101 kPa, or 101,000 Pa, or about 30 inches of Hg. Vacuum is commonly measured relative to atmospheric pressure, and represents a negative gauge pressure but still a positive absolute pressure. You want 21 inches Hg vacuum - i.e. -21 inches gauge, or about 9 inches ...

2

Simply adding another o-ring in series will not give much improvement in the leak rate. This is because the leak rate of the inner o-ring will prevent the internal space (between the two o-rings) from being brought to any reasonable vacuum level so the pressure differential will remain the same on the inner o-ring. However, if you can use a separate pump ...

2

Have you tried a gauge guard? It's a simple diaphragm that allows pressure to transmit, without the liquid crossing the barrier.

2

No, this idea won't work. Except for the start-up transient, there will be no flow of air through all of those holes, and the top (unperforated) plate will still be experiencing the full force of the pressure difference between outside and inside. Better to just stack up N sheets with no holes and no space between them.

2

Condensors in steam plant are a common application - about 90% vacuum and you have to extract the condensate at the rate the engine is using steam - something like 9 lbs per hp/hour if you'll excuse the non-SI units common in steam days. So you may be looking for a boiler feedwater pump which not only works against the vacuum, but into a high pressure ...

2

I am not a vacuum expert, but if you look at the technical data for your pump, you'll find this "Leak rate 6x10-3 Pa m³/s". I take this to mean that your 10 liter = 0.01 m$^3$ vessel will leak at a rate of 0.6 Pa/s. That's pretty slow. You'll want a manual venting value.

2

The difference is the side on which pressure is regulated, and the reaction curve. Typical pressure regulator takes arbitrary input pressure (from compressor) and provides specified (lower) pressure on output, locking the valve as output pressure rises; not allowing it to drop below preset level. The vacuum regulator assures the input pressure is as ...

2

In an atmosphere, the top speed is probably limited by air resistance more than anything, but in a vacuum it would be limited by other factors. Rolling resistance is a major effect that would definitely limit speed. As discussed in the comments, engine rpm would also be a limit if using stock gear ratios. According to a quick google search, the top speed of ...

2

I've owned a hand-held pistol-type vacuum pump, useful for testing distributor advance (yeah, long time ago). A quick search shows the inexpensive versions are capable of 0.6-0.7 atm, not quite what you seek. Additional searching (reading from the links) allowed me to discover a similar design, listed as capable of 0.1 atm. If you require to remove vapor ...

2

Are you going to continue pumping or have intermittent pumping ? As a engineering professor of sealing once told me "everything leaks, it is a matter of how much". Without continued pumping you will not hold that vacuum. For serious leak tight construction I have mostly seen Swageloc connections. NPT has no metal to metal seal , I think metal/metal will be ...

2

Do this: set up the water flow plumbing with the pump OFF, turn on the water flow, and measure the flow rate by running the discharge into a bucket of known volume for a known period of time, and measure the source pressure. If the dents are restricting the flow, then 40PSI (typical for residential water supply pressure) will not result in a 0.15 gallon a ...

2

If I understand correctly, it sounds like you want to make a short carbon fiber tube. This can be done by wrapping the carbon fiber cloth around a mandrel that has the diameter that you want the inside diameter of your tube to be. There is an excellent video that demonstrates the process. Search for “How to make a roll wrapped carbon fiber tube” on ...

2

As far as I know, you can't mold a sphere or cylinder unless the material is on the outside of the mold and you keep the mold in place. Think paper machee over balloons. There is no way to get the balloon out. There is no way to get material to the inside of a hollow mold unless you can spin the material onto the walls, which won't work for carbon fiber. ...

1

eatscrayons suggestion for leak detection is great. However, instead of acetone, I would use isopropyl alcohol (or even better, a helium gas source since He is such a small molecule). It is certainly a small roughing pump so I would not be surprised if you're hitting a floor of 6 Torr. Time to start looking into larger roughing pumps -- those which use oil ...

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