5 ms·

>in a closed-pressure vessel filled with helium at a pressure of 30 bars... >It has a 30-year lifetime, with an easy installation process Normally, any kind o

>in a closed-pressure vessel filled with helium at a pressure of 30 bars... >It has a 30-year lifetime, with an easy installation process Normally, any kind of pressure vessel (steam, compressed gas cylinders, etc.) is subject to routine inspection and hydro-testing for re-certification. What happens if/when it needs to be serviced? Do I need to draw down a crazy level of vacuum before charging it helium (or whatever working fluid)? >Traditional fixed-output units cycle between on and off multiple times a day, switching between zero and maximum capacity to achieve the right temperature balance. But the new heat pump modulates its output to continuously provide the desired temperature. New heat pumps / air conditioners already do this with variable speed compressors and fans.

TylerE 4y ago
There really isn’t such a thing as a “crazy amount of vacuum”. The most vacuum you can have is 1 bar. From a structural standpoint there’s no difference between a very bog standard vacuum, like say the 2psia or so a vacuum cleaner produces and a 10^-10 physics lab vacuum that takes hours of pumping.
- MobiusHorizons 4y ago
  From the stress on the system perspective you are right, hard vacuum is not significantly more stressful on the container than low vacuum. But I think the parent was talking about the cost of maintenance. If the pressure vessel needs recertification over it’s lifetime that will be expensive. If refilling the container requires high purity (and therefore more work removing the air and other contaminants before filling) the process will be even more expensive.
- guywhocodes 4y ago
  This has been a pet peeve of mine for a long time, am I correct to assume that deep vacuum is only hard to maintain because very very small impurities in seals etc will cause a relatively large amount of off-gassing?
  - TylerE 4y ago
    Not only that, but at those levels of vacuum you’re getting all kinds of outgassing from the object in the chamber.
  - s0rce 4y ago
    Helium and hydrogen can also fairly rapidly diffuse through materials or grain boundaries and contaminate the vacuum.
    - usrusr 4y ago
      Should not be a problem here as the vacuum (if it's needed at all) would only be temporary to "make room" for high pressure helium. That would only be required if the helium had to be of particularly high purity and gp wasn't at all implying that this is the case, only that it could be a challenge if it was. From my uninformed perspective, it's just as likely that impurities would condense at the bottom and rest there happily ever after as they would be thrown into an permanent phase change cycle that rims efficiency even in trace amounts. The best case scenario I'd like to read is "actually we don't really need helium but it gives a slight performance edge over other gases and we decided to launch with the setup that gives us the best numbers". No idea if that's close to or very far from reality.
      - s0rce 4y ago
        Yah, I don't think its a problem here, just a general response to the comment about acheiving and maintaining ultra high vacuum.
  - jcims 4y ago
    It also just becomes difficult to motivate the gas towards the intake of the pump. IIRC turbomolecular pumps, which are used for deep vacuum applications, have a large intake area and work by basically spinning a huge array of blades at very high speed to bat the individual gas particles out of the working volume into progressively higher pressure areas, ultimately pumped out by a conventional pump.
- oh_my_goodness 4y ago
  That's true, but according to the article the pressure vessel holds He at 30 bars.
  - TylerE 4y ago
    Ok? The way you test that is by pressure testing it at 35 or 40 bar, not -1
- c_o_n_v_e_x 4y ago
  I should have been more clear. I'm empathizing with the service technician. By "crazy amount of vacuum", I'm referring to amount of time required for pumping / dehydrating the system.
  - TylerE 4y ago
    Dehydrating maybe… pretty easy to depressurize since you can safely vent nitrogen to atmosphere.
Nosep82828 4y ago
[flagged]
nraynaud 4y ago
The default seems to be 4 years visual inspection and 10 years periodic pressure-testing in France (I suspect it's general air compressor). https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000036128632 https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000036128632 I don't have time to read all of that. Skiming, I see the manufacturers have a wide latitude to create their custom maintenance schedule. Interesting detail, the thresholds for inspections are given in uncompressed volume (pression*compressed volume), I guess it's directly proportional to stored energy. I would expect a more relaxed inspection schedule in this instance because there is no significant cyclical loading of the pressure vessel, and since there is no water ingress, internal corrosion should be fine. Vibrations taken as cyclical loading can be swallowed in the bathtub curve, since you get 30000 cycles in the first second, and very little variation of stress at each cycle. edit: - appendix 1 if the vessel has non-corosive gas and not been de-pressurized, internal inspection is not required. Internal visual inspection only if re-pressurizing it and last visual inspection is more than 4 years old. - you seem to be able to replace the water pressure proofing test by an untrasound test under pressure with the nominal gas, but the document describing the procedure ("Guide des bonnes pratiques pour le contrôle par émission acoustique des équipements sous pression") seems to be behind a paywall, so I don't know if it's done at nominal pressure or if you need to open the vessel
- bluGill 4y ago
  Different pressure vessel materials have different characteristics. Just changing the alloy can make a major difference. Since there are thousands of alloys, and new ones are developed once in a while, it would be inappropriate for the law the create one inspection schedule. Plain steel corrodes, so an inspection that it isn't corroded should be done once in a while. Plain aluminum doesn't corrode, so a visual inspection won't find anything, but the fatigue characteristics means that you need to count cycles and stop using it after some number of cycles. There are many other elements that can be used for pressure vessels (though iron and aluminum are most likely), and you can alloy them in different ways. Of course there is more than visual inspection, sometimes ultrasound and x-ray inspections are done, each will show different things, and each requires different training to do.
- jaclaz 4y ago
fsh 4y ago
30 bar is not a lot. A SodaStream CO2 cylinder has twice that at room temperature [1]. The pressure inside your air conditioner is probably not much lower either. I would be very surprised if a 30 bar vessel for an inert gas required routine inspection. [1] https://support.sodastream.com/hc/en-ca/articles/4403801971483-MSDS https://support.sodastream.com/hc/en-ca/articles/44038019714...
ta988 4y ago
If it needs to be serviced, you either vent the helium out (unlikely to happen due to cost of helium thesed days and the volume that will be needed if this becomes a common appliance in households) or move it to another container so you can repurify it at a plant if you are worried about contamination (unsure how much purity those devices need). To refill after maintenance you may also just purge with helium (or another cheaper gas that doesn't impede behavior of the device) then pressurize with helium . So mostly a non issue. And there is really little safety issues with this kind of constant pressure containers containing non toxic gases just a routine inspection should be enough as they can be made of high quality materials and shielded.

TylerE 4y ago

There really isn’t such a thing as a “crazy amount of vacuum”. The most vacuum you can have is 1 bar. From a structural standpoint there’s no difference between a very bog standard vacuum, like say the 2psia or so a vacuum cleaner produces and a 10^-10 physics lab vacuum that takes hours of pumping.

MobiusHorizons 4y ago
From the stress on the system perspective you are right, hard vacuum is not significantly more stressful on the container than low vacuum. But I think the parent was talking about the cost of maintenance. If the pressure vessel needs recertification over it’s lifetime that will be expensive. If refilling the container requires high purity (and therefore more work removing the air and other contaminants before filling) the process will be even more expensive.
guywhocodes 4y ago
This has been a pet peeve of mine for a long time, am I correct to assume that deep vacuum is only hard to maintain because very very small impurities in seals etc will cause a relatively large amount of off-gassing?
- TylerE 4y ago
  Not only that, but at those levels of vacuum you’re getting all kinds of outgassing from the object in the chamber.
- s0rce 4y ago
  Helium and hydrogen can also fairly rapidly diffuse through materials or grain boundaries and contaminate the vacuum.
  - usrusr 4y ago
    Should not be a problem here as the vacuum (if it's needed at all) would only be temporary to "make room" for high pressure helium. That would only be required if the helium had to be of particularly high purity and gp wasn't at all implying that this is the case, only that it could be a challenge if it was. From my uninformed perspective, it's just as likely that impurities would condense at the bottom and rest there happily ever after as they would be thrown into an permanent phase change cycle that rims efficiency even in trace amounts. The best case scenario I'd like to read is "actually we don't really need helium but it gives a slight performance edge over other gases and we decided to launch with the setup that gives us the best numbers". No idea if that's close to or very far from reality.
    - s0rce 4y ago
      Yah, I don't think its a problem here, just a general response to the comment about acheiving and maintaining ultra high vacuum.
- jcims 4y ago
  It also just becomes difficult to motivate the gas towards the intake of the pump. IIRC turbomolecular pumps, which are used for deep vacuum applications, have a large intake area and work by basically spinning a huge array of blades at very high speed to bat the individual gas particles out of the working volume into progressively higher pressure areas, ultimately pumped out by a conventional pump.
oh_my_goodness 4y ago
That's true, but according to the article the pressure vessel holds He at 30 bars.
- TylerE 4y ago
  Ok? The way you test that is by pressure testing it at 35 or 40 bar, not -1
c_o_n_v_e_x 4y ago
I should have been more clear. I'm empathizing with the service technician. By "crazy amount of vacuum", I'm referring to amount of time required for pumping / dehydrating the system.
- TylerE 4y ago
  Dehydrating maybe… pretty easy to depressurize since you can safely vent nitrogen to atmosphere.

Nosep82828 4y ago

[flagged]

nraynaud 4y ago

The default seems to be 4 years visual inspection and 10 years periodic pressure-testing in France (I suspect it's general air compressor). https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000036128632 https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000036128632 I don't have time to read all of that. Skiming, I see the manufacturers have a wide latitude to create their custom maintenance schedule. Interesting detail, the thresholds for inspections are given in uncompressed volume (pression*compressed volume), I guess it's directly proportional to stored energy. I would expect a more relaxed inspection schedule in this instance because there is no significant cyclical loading of the pressure vessel, and since there is no water ingress, internal corrosion should be fine. Vibrations taken as cyclical loading can be swallowed in the bathtub curve, since you get 30000 cycles in the first second, and very little variation of stress at each cycle. edit: - appendix 1 if the vessel has non-corosive gas and not been de-pressurized, internal inspection is not required. Internal visual inspection only if re-pressurizing it and last visual inspection is more than 4 years old. - you seem to be able to replace the water pressure proofing test by an untrasound test under pressure with the nominal gas, but the document describing the procedure ("Guide des bonnes pratiques pour le contrôle par émission acoustique des équipements sous pression") seems to be behind a paywall, so I don't know if it's done at nominal pressure or if you need to open the vessel

bluGill 4y ago
Different pressure vessel materials have different characteristics. Just changing the alloy can make a major difference. Since there are thousands of alloys, and new ones are developed once in a while, it would be inappropriate for the law the create one inspection schedule. Plain steel corrodes, so an inspection that it isn't corroded should be done once in a while. Plain aluminum doesn't corrode, so a visual inspection won't find anything, but the fatigue characteristics means that you need to count cycles and stop using it after some number of cycles. There are many other elements that can be used for pressure vessels (though iron and aluminum are most likely), and you can alloy them in different ways. Of course there is more than visual inspection, sometimes ultrasound and x-ray inspections are done, each will show different things, and each requires different training to do.
jaclaz 4y ago

fsh 4y ago

30 bar is not a lot. A SodaStream CO2 cylinder has twice that at room temperature [1]. The pressure inside your air conditioner is probably not much lower either. I would be very surprised if a 30 bar vessel for an inert gas required routine inspection. [1] https://support.sodastream.com/hc/en-ca/articles/4403801971483-MSDS https://support.sodastream.com/hc/en-ca/articles/44038019714...

ta988 4y ago

If it needs to be serviced, you either vent the helium out (unlikely to happen due to cost of helium thesed days and the volume that will be needed if this becomes a common appliance in households) or move it to another container so you can repurify it at a plant if you are worried about contamination (unsure how much purity those devices need). To refill after maintenance you may also just purge with helium (or another cheaper gas that doesn't impede behavior of the device) then pressurize with helium . So mostly a non issue. And there is really little safety issues with this kind of constant pressure containers containing non toxic gases just a routine inspection should be enough as they can be made of high quality materials and shielded.