compressed shop air

All.
Anyone here ever calculated how much those little leaks on our cnc's cost?
I just brought one of my old Hardinges back online after being a pet
retrofit project in spare moments over the last few years. Of course that long lay off sat in a corner probably screwed all it's seals and within a few days of shakedown testing it was leaking from every part it probably could.
Anyway most of it's leaks are now fixed after spending a few 100 with Hardinge for genuine seals. That much for a few Viton 'o' and quad rings kind of makes you want to look elsewhere but the convenience of them having it here next day won the day.
Just the damn 16c collet closer to attend too.
BUT it did make me look more closely or rather listen for where all those little hisses come from when the shop goes quiet at the end of day. One vmc I spent a couple hours changing 8mm nylon quickfit tubing on today, that ones now quiet, even though the leaks were tiny, in fact inaudible with all its fans on. I reckoned the cost over a year was significant.
One of my customers makes glass tube flowmeters as their main business I might ask them for a low flowrate meter and put it inline on incoming air just to see what the at idle consumption is. I wonder how low we could get it?
Wayne....
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Well, keep in mind that volume loss of air is a function of pressure, so that as pressure decreases, less air is lost per unit time.
But even so, you could measure the pressure loss over whatever time interval yields a reasonably measurable pressure loss, and do kwhrs = V x I x minutes/6000. You could determine the minutes by either watching the compressor kick on and off at the pressure settings (open valves but not using any air), or, pro-rating or extrapolating the kwhrs via a ratio of observed pressure drop to the typical pressure drop in a typical cycle time.
It is amazing to me how rock-solid a valved-off tank can be (indicating a compressor head in good shape), vs the hose/air line losses. If I forget to valve my tanks off, they will be empty by the morning. Valved off, they seem to hold forever.
With the air device popped off the quick disconnect, hold the connect up, fill it with WD 40, and you can often see bubbles right at/within the disconnect, never mind the tool itself, hoses, clamps, etc.
The fadal uses boucou air in the spindle. You can actually shut it off, but the Group Wisdom here (and Fadal's) is not to turn it off, as the coolant somehow mucks up the spindle. I don't quite see how this would happen, but I won't rock the boat....
Kinda makes you want to delay M3 until the very last second. :)
--
PV'd








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DrollTroll wrote:

I don't need to be too scientific about it, just attempt to minimise the leaks. I was at the local bearing/seal stockist picking up some O rings for the barfeeder and it seems many local companies are looking into the same thing. Good for the stockist of course;) I guess it's all down to the recent increases in electricity costs here. 17% hike if I recall correctly.

Or a checkvalve in good shape ;)

I even found a tiny leak on a machines inline air lubricator, around it's lube rate adjuster screw. A quick tweak with a screwdriver seemed to cure that one, it was set to max flow.

Well the above mentioned Hardinge was leaking so bad at idle I could hear the comps tank emptying. Something had to be done. Some of the seal replacements have improved it in other ways though, especially on it's turret.
Wayne.....

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Oh yeah, I forgot, you'll need an amprobe at the beginning and end of the compressor cycle, average them, and then mebbe throw in a motor power factor -- proly .8 to .9. Then $/kwhr, which is always an eye-opener.
Course, whatever this number is, it should be compared to the total cost of compressor operation. It is interesting to see what's what, altho it is possible to OCD on it. :)
-- PV'd
I was at the local bearing/seal stockist picking up some O rings

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With the help of TVA, we did an energy audit a few months ago. The air leaks are an incredible amount of money. Replacing 18 1/4" tube blow-offs (on a sequencer, 3 sec shot 10 sec pause or so) with flat type air knives saves $150,000+ / yr in energy usage. The less those 3x - 450hp compressors are actually pumping air, the cheaper it is expotentially.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Anthony wrote:

I dont doubt it, my bearing/seal supplier is a main agent for SMC and Norgren and told me they now have teams specifically doing these audits in the larger companies.
Of course it helps them sell their products, but I think even at my scale of air usage which is very low compared to say Crown Closures who are just across the road the energy savings are worth it.
Wayne....
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I did the same turret O-ring kit after 14 years was leaking a bunch. Easy to buy from Hardinge than trying to find all the O-rings elsewhere.

Mine is still not leaking but I bought an O-ring rebuild kit for the closer years ago. Looks like 8 or 9 rings in the kit, just looking at the sealed bag.
The CHNC's are made to use air Hardinge says.
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Why wrote:

Probably not quite the same kit, as my machine in question is one of the scarcer HXL toolroom machines with 4 station turret and tailstock. The turret is operated with a rack rather than the air motor of the chnc's
I found the main index cylinder to be badly scored, so had to make a new one.
"
http://homepage.ntlworld.com/fdosdesign/temp/hxl-s/hxl_index_cyl_oldandnew.jpg "
Most of the Quad rings had gone rock hard and fell broke up on removal.

Mine leaks more on collet open. There are a few internal valves and I'm sure thats where the leak across the piston is. I'll know when I get it apart.

Yes. but no dount they can be improved.
Wayne....
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You did a very good job on that.

Could be the O-ring on the valves.

When mine was new it didn't leak very much, over the yrs I noticed it using more air. After the turret kit it's about back to where it was when new ( I also replaced all the stuff behind the turret).

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Another way to save money is to have multiple makeup tanks, each at the max *req'd* pressure for various areas/zones/purposes. This way, someone who only needs 30-60 psi is not being dosed with 120 psi, ditto systems needing only 80-90 psi. Not only do energy savings begin immediately, this strategy has long-term benefits as well, as it is also actually quite a bit easier on the compressor itself, hoses, ears, equipment, you name it. And safer.
Place a regulator *before* the tank, which regulates the pressure *in* the tank (not after the tank, which could restrict volume flow, and is proly tougher on the regulator).
My buddy had shop air at over 180 psi!!! goodgawd... The racket in that place from the air was incredible. Very dangerous, as well.
So I did a two-pressure system for him. Really helped. I don't do this for myself, as my place is pretty small, and I keep my pressure pretty low anyway, cycling between 80 and 120 -- great compressor (HD/Husky, if you can believe it -- incredibly quiet), but crappy pressure controller.
If I had my druthers, I'd feed the fadal at its tool-changing minimum, to save spindle air.
Compressor air is indeed expensive, but apparently it doesn't have to be. There is a french guy making an air powered car, and from the little bullshit web research/calcs I did, it seemed quite viable/economical.
Which makes sense from thermodynamics: Compressors/compressed are not heat engines (altho the piston design is suggestive!), and therefore should not be subject to Carnot's very dismal law of heat engine efficiency. iow, instead of the max 60% possible from a typical IC engine (and 20-30% actually realized), theoretically you should be able to get near-100% of your electrical energy into the compressed air.
So it's just a matter of "doing it right". Some electric motors are themselves 98%+ efficient -- iffin the blurbs are truthful.
I think compressor air seems so expensive not because the compressed air itself is expensive, but rather because its *usage* is so inefficient/profligate, for what it actually does, esp. with heavy-fingered shopsters.
And, an air *motor* may itself be less efficient -- eg, windmills are only about 40-50% eff. in capturing wind energy, due to stalled-air interference with the blades, etc.
So powering air tools is thrice+ removed from the original electrical source: initial electric motor inefficiencies, then losses to the compressor, air line losses, air motor inefficiency. Vs. just a straight electric motor!
Also, Typhoon makes an air gun whose volume output/pressure is quite squeeze-sensitive. Nice. The only problem is that in this model, the air comes out not from a central nozzle tip, but about a circumference, which can make blowing out holes dicey. So I keep both guns at hand. It would be nice to have a squeeze-sensitive center-nozzle type. Not sure if the two styles are mutually exclusive.
You can also have hoses coming off the regulator itself, at a given location. This can make more sense in some scenarios. HF has 3-outlet quick connects, cheap. They proly leak, tho. :)
--
PV'd

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DrollTroll wrote:

The table below highlights the level of wastage created by the smallest of leaks. Hole Diameter (mm)     Air Leakage@7bar(Cfm)     Power Required(Kw/h) 0.5                 0.4             0.06 1.0                 1.7             0.24 1.5                 3.8             0.54 2.0                 6.6             0.93 6.0                 60             8.5 10                 165             23.4
Copied from http://www.directair.co.uk/info/energy.htm
I wonder which type of comp is most efficient?
Reciprocating types probably the worst, but what about Hydrovane types and the various screw compressors.
Wayne....
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...and here's a page from your side of the pond.
http://www.mntap.umn.edu/energy/82-CompAir.htm
"About eight horsepower of electricity is used to generate one horsepower of compressed air" OUCH
Wayne....
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That was my first impression, before I looked into this french guy's compressed-air powered car. I figgered his was a losing proposition from square one, but then somehow concluded that he was right.
Of course, I could have concluded wrong. :)
But the thermodynamics is pretty clear. The integral of PdV (instantaneous pressure times differential volume, which is work or energy -- or Vdp, in this case) should be exactly equal to the the electric power applied, less friction, etc, but less any Carnot efficiency losses. iow, there should be roughly equivalent energy storage/conversion.
But, if your numbers are indeed correct (and not vastly improve-able by design improvements), then this guy's electric car is doomed, and indeed, compressed air is unavoidably and effingly expensive.
But I don't think that figure is correct, because that makes the energy storage efficiency of simple compressed air 50% worse than the *net* energy conversion of a gas engine (and it don't get much worse than a gas engine!), and 80% worse than the Carnot efficiency, not just 50-60% worse, like a gas engine!!
I can't see how that can be. I think it might have to do with how they are then extracting and measuring "power" from the compressed air. And, strictly speaking, one should be comparing energy (joules, btu's, cals, etc), and not power (watts).
It could be that the compressed air, if compressed by a 1 hp motor, cannot effectively release its energy at a constant *rate* of 1 hp, and perhaps much less. BUT, The air should be able to release the overall equivalent amount of total *energy* that the motor supplied. I think they might have inadvertently factored in the inefficiency of some engine or turbine used to then measure the stored energy of the compressed air.
One way to fairly measure the equivance of energy storage is the following: Run a 1hp motor for x minutes, let it raise a weight. Calc the energy input, and mgh. Run the same motor for the same net energy expenditure (kw-hrs) in compressing air, then let the air expand, see how high it can lift the same weight.
The diffs. will reflect the energy efficiency of compressing air.
Also matters how air is compressed/expanded: adiabatically, isothermally, etc. Can make a big diff.
--
PV'd, hopefully not by thermodynamics, this time. :)


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DrollTroll wrote:

Not my numbers! University on Minnesota's Numbers.
Seems the common consensus amongst these people is that compressed air is damn expensive, and back to my original point the real cost of Leaks, even small ones.
Anthony gave some figures from an actual Audit at his large facility and I can well believe it.
The various types of compressors have a large bearing on this too. Piston types are probably less efficient than a modern IC engine. My own compressed air requirements are fairly low actually, but I'll be looking into getting a more modern compressor in the near future.
In the meantime I'm spending a little time to improve the actual yield on the air my current compressor is producing.
It seems here in the uk 0% interest finance is available on more efficient systems.
Wayne...
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See http://en.wikipedia.org/wiki/Compressed_air_energy_storage
The theoretical energy transfer from motor to air is 100%, joule for joule. It winds up being much less than that, of course, but still way more than what you get from an IC.
At least according to the contributors to wiki. :)
But which, as I've argered previously, almost *must* be the case, because it is energy transfer (with perhaps some heat losses, but most recoverable) and not energy derived from heat, as in a true engine, and therefore not subject to Carnot-type efficiency constraints. Which doesn't mean there aren't significant design hurdles, but hurdles of a different type than in IC etc. That "8 for 1" stat cited was sort of out of the blue (I thought it was from the U's own research), and I suspect it is very context-sensitive, possibly a net-net-net efficiency of how we use the air, not a theoretical energy transfer efficiency -- and hopefully not applicaple to cars!!!
But that was a digression anyway.
More germane to this thread is what a couple of sites list as ways to save money with air. http://www.ceere.org/iac/assessment%20tool/ARC2420.html#1RP ( but whose calculation buttons unfortunately don't work) .
In addition to the obvious, such as fixing leaks, getting better compressors/motors (of which variable-speed drives is a dicey choice, according to one site), they cite simply "using less air"!!!
But, toward this end, they *do not* mention using different makeup tanks for different pressure applications, which I think is a biggie. They do mention things like different nozzle design, etc.
Another thing they mention, sort of akin to makeup tanks, is staging smaller compressors. Along these lines, I think an undersized compressor running longer may have some advantages, in a bigger tank, if absolute cfm is not a major issue.
A major thing they cite is temp of the incoming air! So much so, they recommend putting the compressor outside, if possible (assuming it's cooler outside), *and in the shade*!
My ideas would be to take cold water, such as that headed to the inlet of a HW heater (or not -- but this would serve as a kind of preheat for the HW tank) could be used to cool hot intake compressor air, by running it through HVAC type A coils, over which blows intake air. These types of coils can also be used to passively dry the air upon leaving the tank. This would require a "collection plenum" (just big-diameter plumbing for a brief stretch) after the coil, with drain.
Lastly, they mention un-contorted clear plumbing, for least drops in air pressure, so the set point of the compressor can be as low as possible. Even tho dedicated make-up tanks will help with this, still, a lower *net* pressure at the farthest delivery point in the highest pressure environment will lower the max pressure at which the compressor itself will operate. Regulated makeup tanks are essentially for conserving volume flow, and thus compressor on time.
So if you have a pressure drop of 15 psi at your farthest point of highest req'd pressure, and can re-plumb so that the drop is only 5 psi, you'll then be able to lower the main compressor regulator by 10 psi, which is a lot, efficiency-wise.
I shoulda been a bean-counter. :) I got digital VOMs all over (three at a time), monitoring my kluged rpc. And a big-assed analog VOM in my office, monitoring Yonkers' shitty voltage, which most people think is a broken clock. <doh> :)
--
PV'd



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DrollTroll wrote:

Drive train efficiency and friction all all enter in the equation just like in IC engines.
I wonder how efficient the reed valves in your average piston type compressor are compared to a well designed and timed poppet valve in an IC engine. It's like comparing apples n oranges probably.
I think the piston compressor in the form we all know (and loathe) doesn't have too much going for it.
Wayne....
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Well, the big diff is that IC engines have fundamental ceilings to their efficiencies -- as might solar cells.
Things like hydroelectric plants, motors, any kind of energy *transfer* (air in this case) are theoretically 100% efficient, and go down from there. IC engines start at 50-60%, and go down from there. Other heat engines proly start even lower, but their fuel sources may have other advantages.
I always thought the smegma in a volcano was a great heat source -- dicey, but great.
As far as compressor choice/type: As long as it's not a Sears aluminum oil-less. :)
I esp. like the idea of putting the compressor outside -- better yet, right up next to the neighbor's property line. :) :)
My buddy is equipping is garage/shop, and put a big-assed make-up tank outside. Space-saving is one of the advantages to a series of smaller tanks as well (individually regulated or not) -- you can put them where they fit.
Did I say "smegma"?? I meant, of course, "magma".
--
PV'd


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Power

There are federal and state rebate programs that will rebate part of the cost of a newer energy efficient air compressor. Check with your local power utility. But beware of claimed savings and read this article first:
<http://www.plantservices.com/articles/2007/099.html
Despite the gloomy findings, upgrading from a piston type compressor is usually a no-brainer.
Also there are a couple of months left to take advantage of the section 127 investment tax credit.
<http://www.section179.org/section_179_calculator.html
There probably will be no better time to buy a new compressor than before the end of the year.
--

Dan

CNC Videos - <http://tinyurl.com/yzdt6d
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