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Author Topic: Efficiency question: Barco Jackhammer - Simple old technology  (Read 20660 times)

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #25 on: 11/08/2009 23:22:59 »
I think I see your idea but don't you need bang and squash to coincide as that's the only way to get the compression: letting the engine do it for you?
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #26 on: 12/08/2009 14:04:14 »
Not if you use the tool's weight to compress the air/fuel - although I concede that the tool would be incredibly heavy or the cylinders being seriously undersquare (for higher pressure for equal force).

I see that one piston could drive the compression of the other, but that seems to defeat the object of the design.
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #27 on: 12/08/2009 14:12:17 »
The energy used for compression is tiny, compared with the energy from the ignition stroke. After all, mutticylinder, rotary engines do this, effectively.
I can't see a system being popular if the operator had to provide his own compression effort!
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #28 on: 12/08/2009 14:58:32 »
I've been thinking. Perhaps the existing ones must be two Stroke engines???
The link seems to suggest it is.
« Last Edit: 12/08/2009 15:01:56 by sophiecentaur »
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #29 on: 12/08/2009 18:37:00 »
Yes. I'm sure they are (two stroke).
Obviously, it's hardly advanced technology even for its time!

I'm not suggesting the operator has to provide the compression each time just to start then the process then the weight of the hammer takes over.
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #30 on: 12/08/2009 18:55:10 »
I remember hearing that wonderful "Doompha Doompha" sound, as a lad. The operator was the coolest one in the team.
Having read more about it, I think you're prob right that two, four stroke halves would be more efficient than the single one. But I'm still not sure of the timing.
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #31 on: 12/08/2009 21:20:03 »
I don't know how 'cool' I'd feel operating one of those big ol' things - petrified more like!!  You'd certainly need balls-of-steel (plus toes of steel) to use one of those all day!

I think the timing would be relatively straight forward - just replace the cam shaft with a ratchet.
« Last Edit: 12/08/2009 21:26:20 by peppercorn »
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #32 on: 12/08/2009 23:54:19 »
I was referring to the relative timing of the two cylinders!  :-\
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #33 on: 13/08/2009 11:04:02 »
I was referring to the relative timing of the two cylinders!  :-\
Is it not just: one goes bang whilst the other sucks clean air - i.e. 180° out of phase?
« Last Edit: 13/08/2009 11:06:27 by peppercorn »
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #34 on: 13/08/2009 14:03:42 »
But, as I said, if you 're talking fourstroke, I think that the phase isn't right the other way round.

I guess it calls for a picture of the workings you have in mind.
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #35 on: 16/08/2009 13:58:03 »
Here's how I imagined it (whilst running):



I have illustrated for spark ignition, but Diesel will be the same cycle.
The cylinders are labelled 1 & 2 with each stage shown down the page.
The bang of one cylinder powers the hammer back up (the conn rod fixed to the hammer end) & draws clean air for the other cylinder. The weight over the cylinders works to compress the gas prior to ignition & exhaust the gas for the other cylinder.
« Last Edit: 16/08/2009 14:06:51 by peppercorn »
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #36 on: 16/08/2009 23:18:34 »
Nice pictures. I see what happens.
You get four stroke efficiency and a bang every time.
There is the same trade off as with a big single pot 2stroke or a twin 4stroke motorcycle engine. It can't 'rev' at a different rate- it needs to dumpha dumpha at the same rate.
You will have one explosion each time from a half capacity cylinder instead of the less than full capacity two stroke power stroke.
There is the weight factor. The whole thing can't be much heavier. But the standard model is probably very heavy in any case, so probably not relevant.
What about the symmetry of the load on the machine? It's no longer coaxial as it has two parallel pistons. A lot of highly impulsive loads could be an embarassment to this slick new piece of kit.
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #37 on: 17/08/2009 10:01:23 »
Yes. There would be a tendency to rock the operator from side to side. Maybe it would need some kind of half weighted flywheel (although reciprocating not rotating) to cancel the lateral effect.
Ford used off-centre weighted flywheels on their V4 engines, I think.

Maybe this technology would be better suited to braking up material fed in to a stationary device. As I alluded to earlier, the design could partly pulp waste wood or other dry biomass in batches as a step in bio-fuel (or similar process) production.
« Last Edit: 17/08/2009 10:04:24 by peppercorn »
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #38 on: 17/08/2009 11:36:17 »
IS it all appropriate for a device for pounding roads? It is getting a bit like fitting a gunsight to a clubhammer!

Bearing in mind that all the effective compactors use high frequency impulses nowadays, I think that the Jackhammer, charming as it is (and I'd love to play on one), is probably a dinosaur.
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #39 on: 18/08/2009 14:31:54 »
Maybe this technology would be better suited to braking up material fed in to a stationary device. As I alluded to earlier, the design could partly pulp waste wood or other dry biomass in batches as a step in bio-fuel (or similar process) production.

Beats using electric motor or 2-stroke driven machines...
« Last Edit: 18/08/2009 14:34:05 by peppercorn »
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #40 on: 18/08/2009 22:42:45 »
Except that the frequency is, necessarily, very low. This is because there is a large mass which falls under gravity. A rotational system gets over this - which is probably why the jackhammer and beam engine are the only examples I can think of which don't use rotation!
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #41 on: 19/08/2009 10:28:08 »
Yes, of course! Return under gravity is the limiting factor here - I should have realised that!
Although slow & steady might not be a bad thing for every application.


Alternatively, like I think you were alluding to previously, using opposing stokes would overcome this:


The yoke is just for timing the two cylinders and is shown massively over-engineered here for illustration. Power is the red arrows (on alternate strokes).
Clearly, this will only work for two-stroke, but a bit more thought could make a 4-stroke equivalent.
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #42 on: 19/08/2009 14:10:00 »
Quote
Alternatively, like I think you were alluding to previously, using opposing stokes would overcome this:
'fraid not - the hammer can't fall any quicker however many times you lift it up. If you fire very frequently the hammer will merely be suspended at a higher average position. It won't return to the fully compressed position if it isn't given time.
See how clever the use of a rotary system is? The speed is only limited by the breathing and the strength of the components.
 

Offline peppercorn

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #43 on: 19/08/2009 16:48:53 »
Bugger! Really must engage brain!

The original configuration (both pistons in sinc.) would work if material being broken up is forced back up against the hammer (a bit like if the barco was suspended on an A-frame pinned to the ground with a big spring pushing it back down each time). So pulping wood, etc could conceivably utilise a high speed hammer action of this sort.
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #44 on: 19/08/2009 18:15:40 »
Yes, a spring would do it.
Though, there would still be the problem /consideration that your system would have a resonant frequency, set by the mass and spring constant.  Sodding great spring and sodding strong A frame needed!
 
I have just thought of a possible advantage in that the stroke of the system would not have to be constant (unlike the stroke of a rotating engine) so it wouldn't 'stall' but just carry on vibrating with smaller amplitudes.
 

Offline Geezer

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #45 on: 20/08/2009 05:25:09 »
Regarding efficiency, would it be possible to derive some measure of useful work done from the heat generated in the rock? I imagine there must be quite a lot of friction produced while the rock is getting smooshed. (Not to mention the heat coming out of the operator's mouth when the thing lands on his toe.)  :o

Measuring the temperature increase might be a bit tricky, but perhaps not impossible if you had some sort of "calibrated" rock in a well insulated setup.

 

Offline nicephotog

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #46 on: 21/08/2009 13:53:15 »
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If the rock it is trying to break up doesn't break - or if you try to break up a trampoline (see above) then there is no useful work.

I'm well aware that work-done is an expression of used-levels-of-resource-expended-SUCCESSFULLY.

It's in context of fuel used per strike / per time to achieve the cycle of load - reload in the sequence of moving the hammer,
the fuel yield and gravitational attraction and inertia never will actually change(at least for the fuel grade).
 

lyner

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #47 on: 22/08/2009 23:06:52 »
The clue is in the term 'useful work' which is essental to know before you can calculate efficiency.
If you can't specify that then you can't know the efficiency. The only hope of some sort of idea would be amount of flattening of a specific thickness of Tarmac or breaking of a specified sample of stones. Neither of these could easily be related to 'real life' work situations.
 

Offline Geezer

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #48 on: 23/08/2009 05:39:55 »
All measurements of efficiency MUST be related to "real life" situations, otherwise they are entirely meaningless. There is a set of "real life" assumptions behind every measure of efficiency. They may be explicit, but they are more commonly implicit.

In the case of the "instrument of dread" in the photo, its main purpose is to compact aggregate and soil. Devising a method of comparing its effectiveness compared to the alternative methods should not challenge your average fifth year pupil too much.
 

Offline nicephotog

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Efficiency question: Barco Jackhammer - Simple old technology
« Reply #49 on: 24/08/2009 03:25:55 »
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sophiecentaur: Neither of these could easily be related to 'real life' work situations.

Would measuring the resultant "mode" of the tarmac p/cm and in a grid do that?
avg.pdf www.nicephotog-jsp.net fortran95 "Plato IDE"
What a thought for MATLAB
« Last Edit: 24/08/2009 03:30:45 by nicephotog »
 

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Efficiency question: Barco Jackhammer - Simple old technology
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