Idea: How to Search for an Air Compressor

[Sandyn]

I'm an engineer, I don't really believe in impulse stuff based on vague ideas, or a few inconsistent remarks from someone on a Forum who might well not know what he's talking about.

Well, it's not a very constructive comment, and he DOES remind me of the lame brains in high school class.
Pretty funny actually, the head lame brain made a smart-*** comment, and the Geograhy teacher, very cool guy, said "Greg (said lmne brain), you know in 10 years time you will be working minimum wage, if you are lucky, and have a guy exactly like Alan as your boss".

And you know what.....well, I wasn't his boss, but Greg DOES work min wage pushing an silly person stick around....
Nothing WRONG with that, but he sure doesn't like it.

Hey, chill out. The comment was meant in fun, but I sincerely apologise if I have somehow offended you. It's never my intention to do that. I'm Scottish so our humour is often based on being able to laugh at ourselves (and others). We love to observe the humour in daily life. I just thought, "well there's an 'Engineer' who seems to have all the answers, but he can't choose a compressor". I still think it's humorous. sorry.
I'm absolutely not offended in any way about your insinuation that I'm some lame brain and don't know what I'm talking about. You are probably correct. As for minimum wage! I wish I was smart enough to get the minimum wage!! I'm so stupid I have to pay my boss to go to work!! The really funny thing is, apparently I'm stupid, but it only took me 5 min to choose a compressor, so being really clever doesn't seem to be a great advantage?
You seem to know your stuff, so chill out, welcome to the forum and enjoy.

 

[baldkev]

Is same as if you have a car with annoying grinding or sqealing sounds: turn your radio up.
Voila, all that goes away.
If leaking oil begins to blur the windscreen, you can add a better degreaser in your wiper fluid to deal with that.
If the smoke from the engine starts to obscure your vision, that's harder to address.
Usually the best solution to that is to increase insurance, and leave car parked with keys in it.
That solves everything.

Ahhh, you have owned a few fords

 

[TRITON]

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[TRITON]

Hey, chill out. The comment was meant in fun, but I sincerely apologise if I have somehow offended you. It's never my intention to do that. I'm Scottish so our humour is often based on being able to laugh at ourselves (and others). We love to observe the humour in daily life. I just thought, "well there's an 'Engineer' who seems to have all the answers, but he can't choose a compressor". I still think it's humorous. sorry.
I'm absolutely not offended in any way about your insinuation that I'm some lame brain and don't know what I'm talking about. You are probably correct. As for minimum wage! I wish I was smart enough to get the minimum wage!! I'm so stupid I have to pay my boss to go to work!! The really funny thing is, apparently I'm stupid, but it only took me 5 min to choose a compressor, so being really clever doesn't seem to be a great advantage?
You seem to know your stuff, so chill out, welcome to the forum and enjoy.

I agree. nothing to get so upset about, it was a clear observation.
What I fail to see is the point of this tread. It appears to be all about the data, rather than any sort of need of a compressor.

 

[Keith 66]

^^^^^ Exactly, First what do you need a compressor for? If you want to drive a little airbrush a tiny diaphragm one will do, if you want to sandblast you will need a monster! In between is a multitude of sizes.
Main thing is FAD, Second is Horsepower of motor, If you have 3 phase power happy days as you can then get a nice big Ingersol rand VTwin type 15 or 30 & have tons of air. If you only have single phase you will be limited to approx 3 hp & that means high revving noisy machines of about 12 cfm or a bit more.
As for getting failed test scuba tanks to use as receivers? If a tank has failed test they chop a hole in it, they have to. Would you trust joe blogs of the street not to sell it on ebay ? I wouldnt.
Buy the biggest compressor that will run of the supply you have!

 

[Sandyn]

I'm sure you have found SGS. already. They have a great range of compressors, at good prices. They are probably all badged. There is some useful information on the site as well.

As a peace offering, I have attached a manual on Multi-Criteria_Analysis it's aimed at local government, but the principle applies to any decision making.

 

[mcgranag]

...............- Thermal aspects: degree of active/passive cooling...
One aspect that's not been mentioned, is in some places the cost of electricity varies during the day.
And you might have some supply of your own: solar, wind etc.
I have not looked at it carefully, but in principle you MIGHT be better off having a BIG high pressure receiver that you pressurise when the sun is shining, the wind is blowing, ort rates are lower (say after 19h00).
The idea of using pressurised air as energy storeage IS used, and you'd need to see if you can get a big enough tank to make it worth your while.


.......The design methods it specifies are pretty relaxed, basically:
- Design for 5 x Design WP
- No specific provision for corrosion
- Welds are not 100% NDE, but rely on welder qualification and batch tests
- Hydro/pneumatic test (with quite a relaxed requirement of 150% of Design WP)
- Material requirements pretty wide open, and some attention is given to toughness, but nothing very rigorous, and especially not to CONSISTENCY of mechanical properties throughout a BATCH of supplied steel
- Welds are NOT checked for mechanical properties, they rely on general certification, and in effect on the final hydro/pneumatic test

And no attention to failure by fatigue.

I have two observations on the above regarding (i) Thermal energy, and (ii) fatigue

(i) Compressed air is not a good energy storage medium, unless significant care and equipment is used. Once air is compressed as well as reducing volume, it increases in Pressure, and in Temperature. Once stored in a receiver, the pressure might still be there the next day, but the temperature generally isnt. This loss of thermal energy to ambient can be high and is a significant obstacle tor using compressed air as an energy storage medium. Compressing the air to higher pressures become more difficult in machinery terms too (think seals, leaks) and also with respect to temperature increasing further (think diesel engine). These factors are why most everyday compressed air systems are around 5-9 bar. For energy storage or recovery, small systems are not worth it.

(ii) Fatigue is likely not an issue. If the receiver is designed for 5x WP as written above, then that probably means that internal stresses in the receiver reach a max of 20% of UTS (ultimate tensile strength) in the worst case scenario. Fatigue in ferrous metals is only an issue above around 40% of the UTS. Once the air receiver stresses are kept below that value within their designed working pressure, then fatigue will not occur regardless of number of cycles. Non ferrous metals are a different matter, where every cycle can contribute to fatigue failure.

 

[mcgranag]

........................
- Plastic deformation: aluminium deforms under all loads, whereas steel only deforms above YIELD
.........................................

I'm not sure what you mean by deform here? Surely both aluminium and steel exhibit elastic behaviour before the Yield point, and plastic behaviour after? In both metals, any deformation below yield pt will be temporary, and above yield pt will be permanent?