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Calculating heat dissipation requirements for high pressure compressor... ?
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max_torque:
I'd also add that typical pneumatic actuator systems run at about 10 bar.  Very few systems run any higher than this becase the efficiency tumbles, safety is difficult to maintain and you can get plenty of power / force from "just" 10 bar.  A robot using even 10 bar sounds reasonably dangerous to me (and you'll find that valves and other components are expensive and difficult to source)

it seems to me that this is the classic case of "i've made up my mind i'm doing it like this, now help me to do it exactly like this" when it's frankly immediately obvious that you REALLY don't want to do it like that at all..........

BTW, you will also need to check what machinery and HS&E directives cover high pressure systems, even in domestic settings  (like for example those SCUBA tanks, which despite being "recreational" in useage are still explicitly covered by various safety directive due to the very real risks they pose)
pipe2null:

--- Quote from: NiHaoMike on May 21, 2020, 01:36:26 pm ---An alternative is to do destructive pressure tests with water, which can be done with an off the shelf pressure washer.

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--- Quote from: max_torque on May 21, 2020, 05:17:22 pm ---er, nobody tests high pressure air systems to failure with high pressure air!!

If you need to carry out burst/failure tests, do it hydraulically like everyone else.  Costs are small, safety is maximised.   In the UK, i would be in breach of a large number of laws if i were destructive testing high pressure air systems in any domestic environment.

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This makes a helluva lot of sense, and is the direction I will go for destructive tests.


--- Quote from: max_torque on May 21, 2020, 05:22:44 pm ---it seems to me that this is the classic case of "i've made up my mind i'm doing it like this, now help me to do it exactly like this" when it's frankly immediately obvious that you REALLY don't want to do it like that at all..........

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Yes and no... You are partially correct, and completely correct on the first "I've made up my mind I'm doing it---" part, but I am pretty flexible on the "how to do it the best way with minimal resources, while maintaining safety requirements" side of things.  I've been running down the HPA path because that's the only idea I came up with for destructive testing and until now I was unaware of the alternative.

I hate being wrong, but thank you for correcting my ignorance.  ;)
skylar:
For 3k to 120PSI reduction there are dedicated HPA products aimed at paintball/airgun market. I have one, works ok for low volume use. Also paintball gun regs will drop 4k to 800psi and you can go from there as an intermediate stage. Welding regs take 2-3kpsi to 15psi or so, so not good for your needs.

Keep in mind that if you use the HPA for breathing at all, you really should not connect it to a LP system to prevent contamination. Also keep track of what lubricants you use, particularly in the HPA side to avoid an O2 ignition as I mentioned in my first reply. Sure you can get away without these considerations, until you don't, rapidly.



--- Quote from: IanB on May 21, 2020, 06:43:53 am ---
--- Quote from: coppercone2 on May 18, 2020, 09:47:52 pm ---PV = NRT is correct
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Not so much, actually. It is sort of true in high school science classes, but it leaves out a lot of thermodynamics that happens in real world scenarios. In particular it doesn't apply to air compressors as it tells you how any two variables are related if the other variable is held constant. So you can do P vs V at constant T, or P vs T at constant V, for example. If you compress air then P, V and T are all changing at the same time and a different formula applies ( \$Pv^\gamma=\textrm{constant}\$ is the basic one).

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This is it! This equation and compressors are not a static condition is why my thermal numbers are so much higher than others using just PV=nRT. You have to consider the change in condition, not the final state. PS: The 840W required energy is the compressor input and not the air heat output, therefore you need to cool the heat from compressor inefficiency (35% minimum I'd guess; 15% from motor, 20% from seal friction/valves) and the air compression heat.


--- Quote from: max_torque on May 21, 2020, 05:17:22 pm ---er, nobody tests high pressure air systems to failure with high pressure air!!

If you need to carry out burst/failure tests, do it hydraulically like everyone else.  Costs are small, safety is maximised.   In the UK, i would be in breach of a large number of laws if i were destructive testing high pressure air systems in any domestic environment.

If you want an air gun, fair enough, just use the normal small capacity cylinders designed explcitly for this. Your local dive shop or air products place will fill that cylinder for you  very cheaply!

--- End quote ---

Seconded, also hydraulic failure is less likely to send the broken bits to the extremes of your safety cage making post-failure analysis much more useful. Pneumatic failures often leave little intact to access, particularly in brittle plastics.

An interesting side note, often you will see HP hydraulic systems (oilfield) tested with HP N2 (in R&D, not in production/service) so as to ensure that an air tight seal will surely contain an oil/water fluid (due to the relative molecular/atomic sizes in play, high vacuum systems are often tested with helium). 15kpsi of N2 is fun stuff and these days I hear (I changed industries 5 years back) they're up to 30kpsi in the offshore safety equipment, no thank you.
tautech:

--- Quote from: skylar on May 26, 2020, 05:05:04 pm ---For 3k to 120PSI reduction there are dedicated HPA products aimed at paintball/airgun market. I have one, works ok for low volume use. Also paintball gun regs will drop 4k to 800psi and you can go from there as an intermediate stage. Welding regs take 2-3kpsi to 15psi or so, so not good for your needs.

--- End quote ---
Actually oxy regs will allow for 150 PSI IIRC (not got one in front of me) but their flow rates will be only suitable for dusting without another storage cylinder to buffer the flow rate losses and certainly not enough to run other than small air tools.
skylar:

--- Quote from: tautech on May 26, 2020, 08:06:46 pm ---Actually oxy regs will allow for 150 PSI IIRC (not got one in front of me) but their flow rates will be only suitable for dusting without another storage cylinder to buffer the flow rate losses and certainly not enough to run other than small air tools.

--- End quote ---

Fair, I was thinking about your cheap MIG/MAG/TIG/etc. regs that only have flow adjustments, no PSI adjust.
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