Why waterjet? Why not OILjet?

[Downunder Bob]

Perhaps a pump of a multi cylinder engine, with all ports going into a manifold, just have to make sure the diesel is clean those pumps hate dirt even fine particles. They also hate water. If you could get a pump off an old truck, get the filter as well and put a new element in it. drive it with a high speed electric motor, probably need a few HP.

An old semi I drove years ago used to get 5 mpg so at top speed say 50MPH That was at 2500 RPM, but you could run it faster than that probably double that's about 10 gph should be enough. Find out the size of the injector nozzles and multiply that by how many injectors, mine had 8, and that will give you a nozzle size.

 

[strantor]

Perhaps a pump of a multi cylinder engine, with all ports going into a manifold, just have to make sure the diesel is clean those pumps hate dirt even fine particles. They also hate water. If you could get a pump off an old truck, get the filter as well and put a new element in it. drive it with a high speed electric motor, probably need a few HP.

An old semi I drove years ago used to get 5 mpg so at top speed say 50MPH That was at 2500 RPM, but you could run it faster than that probably double that's about 10 gph should be enough. Find out the size of the injector nozzles and multiply that by how many injectors, mine had 8, and that will give you a nozzle size.

Let's see... 5MPG @ 50MPH
1hr = 50mi = 10gal. (10GPH) = 0.83GPM
That's about in the right ballpark. A 30HP waterjet might put out 0.65GMP @ 60,000 PSI. [ex]
If I can get a diesel injection pump to put out 0.65GPM at half the pressure, half the HP, that might be a target worth shooting for.

When you say they don't like water, how do you mean exactly? they get rusty inside, or? Will they physically pump water?

What if I run water, and each time before I put it to rest I flush the water out with diesel, let it sit in the unused state with diesel so it doesn't rust up?

 

[MontanaLon]

I think using anything even remotely flammable is not going to work. When the abrasive strikes the metal there will be heat generated. You may not see sparks when waterjet cutting but you can be sure the temperature is rising at least to the point of boiling the water and likely higher. Diesel will autoignite at 410* F. It is why diesel engines run without spark plugs. The pressure is increased to the point the vaporized diesel catches fire on its' own. Only way to prevent it would be to eliminate oxygen in the system. Flood with CO2?

And the flash point of diesel is quite low so any source of ignition in the area would be a real problem. Will the motors used to drive the carriage create any sparks? Will any of the components reach the temperature of auto ignition?

Water is used because it is cheap and can't be made to burn. You really need to focus on figuring out a way to pump it at the pressures needed using off the shelf parts.

 

[matthewsx]

Let's see... 5MPG @ 50MPH
1hr = 50mi = 10gal. (10GPH) = 0.83GPM
That's about in the right ballpark. A 30HP waterjet might put out 0.65GMP @ 60,000 PSI. [ex]
If I can get a diesel injection pump to put out 0.65GPM at half the pressure, half the HP, that might be a target worth shooting for.

When you say they don't like water, how do you mean exactly? they get rusty inside, or? Will they physically pump water?

What if I run water, and each time before I put it to rest I flush the water out with diesel, let it sit in the unused state with diesel so it doesn't rust up?

I doubt "pickling" any type of pump designed to run oil (kerosene, diesel, etc) will prevent the damage likely to happen with running water through it. The design parameters are probably too different for it to work. Oil has good lubricating properties (film strength, etc.) at room temperature and zero PSI while water requires a very high pressure to act as any type of bearing.

If you really want to know then go ahead and try running water through a hydraulic pump, or oil with suspended garnet through the same part. Just stand back from it when you start it up. I'd also confine experiments to stuff you can get at the scrapyard for a few bucks rather than expensive new parts.

I do love the intellectual exercises posed by things like this, our forum allows for any kind of question you want to ask and for others to respond honestly and respectfully in turn. However, the laws of physics apply to everything in our universe that I'm aware of and I can almost guarantee that if there was a good way to do some of the things proposed here professional engineers would have done it.

My dad had two things he always would come to when discussing stuff like this around the kitchen table. First, the second law of thermodynamics

Second law of thermodynamics - Wikipedia

en.wikipedia.org

Seems like people are always trying to get around it but nobody has figured a way yet.

Second, the mystical properties of a material he called unobtanium,

Unobtainium - Wikipedia

en.wikipedia.org

if only we could source it somewhere we could easily defy the laws of physics that stymie so many great ideas....

Cheers,

John

 

[strantor]

I think using anything even remotely flammable is not going to work. [...] Water is used because it is cheap and can't be made to burn. You really need to focus on figuring out a way to pump it at the pressures needed using off the shelf parts.

Yes I think I agree. And I am starting to think this is the way:

Why not just use antifreeze....ethylene glycol. No rust there and somewhat better lubricant characteristics for the pump.

So a diesel injection pump moving the green stuff; think that'll work? I've confirmed the viscosity of 50/50 mix is about right, and it has corrosion inhibitors to prevent non-stainless guts from rotting. The only thing I still wonder is about the lubricity of it. It's got to be a better lubricant than diesel, right?

What about fog/mist or even just vapor in the air? Lung cancer expres

 

[strantor]

I doubt "pickling" any type of pump designed to run oil (kerosene, diesel, etc) will prevent the damage likely to happen with running water through it. The design parameters are probably too different for it to work. Oil has good lubricating properties (film strength, etc.) at room temperature and zero PSI while water requires a very high pressure to act as any type of bearing.

If you really want to know then go ahead and try running water through a hydraulic pump, or oil with suspended garnet through the same part. Just stand back from it when you start it up. I'd also confine experiments to stuff you can get at the scrapyard for a few bucks rather than expensive new parts.

Thanks for the pointers!

[...]the laws of physics apply to everything in our universe that I'm aware of and I can almost guarantee that if there was a good way to do some of the things proposed here professional engineers would have done it. [...] if only we could source [unobtainium] somewhere we could easily defy the laws of physics that stymie so many great ideas....

You made a similar comment on my compressor thread:

To answer the actual question about what limits things it's physics. It might be possible to modify an existing compressor pump as you've suggested but the fact of asking about it probably means the engineering required isn't available in-house.

Back then I thought it was meant as a thinly veiled condescending insult, so I ignored it. In retrospect I realized that it was actually a motivational speech and it helped me achieve my goal. So I appreciate the continued support, unconventional as it may be!

P.S. I am an Engineer; just not a ME. If I were doing this in a professional capacity I would be a member of a team whose collaboration would preclude me asking stupid questions publicly. This forum is the only team I have. While I don't have a Mechanical Engineering degree or equivalent decades of experience, I do have an above average grasp of physics and a natural aptitude for mechanics, as do the majority of the members of this forum I suspect, plus hundreds of years of combined experience - that's why I'm asking here and not elsewhere. I am familiar with the laws of thermodynamics; no lectures necessary. Or maybe I've overestimated myself; maybe you can explain how using a fluid other than water to carry a jet of abrasive particles demands a breach of the laws of physics?

 

[strantor]

I have studied a bit now on the pharmacology of inhaled antifreeze vapor/aerosol and it seems to be, if anything, a mild irritant; not toxic or carcinogenic. Since I would probably have this semi-outdoors, under a lean-to (I wouldn't want any mist, incl./esp. water mist wafting through my shop) I consider 50/50 ethylene glycol antifreeze solution to be a nonhazardous (if messy) viable transport medium for the garnet. In the next few days I intend to order a used CP3 CRDI fuel pump (23,500PSI) to test pumping antifreeze. If anyone knows for a fact or has a strong informed hunch that this fuel-pump-pumping-antifreeze scheme won't work, please speak up and save me some money.

 

[brino]

@strantor

geez I love reading your threads!
I always learn so much from all the tough questions and suggested answers.

It is obvious that you know a great deal, and just need a sounding board.

This quote:

If I were doing this in a professional capacity I would be a member of a team whose collaboration would preclude me asking stupid questions publicly. This forum is the only team I have. While I don't have a Mechanical Engineering degree or equivalent decades of experience, I do have an above average grasp of physics and a natural aptitude for mechanics, as do the majority of the members of this forum I suspect, plus hundreds of years of combined experience - that's why I'm asking here and not elsewhere.

sums it up beautifully!
It is also the reason I spend so much time here myself.

I don't believe that I have contributed any answers, but am glad to be listening in on your team meetings!

-brino

 

[Downunder Bob]

Let's see... 5MPG @ 50MPH
1hr = 50mi = 10gal. (10GPH) = 0.83GPM
That's about in the right ballpark. A 30HP waterjet might put out 0.65GMP @ 60,000 PSI. [ex]
If I can get a diesel injection pump to put out 0.65GPM at half the pressure, half the HP, that might be a target worth shooting for.

When you say they don't like water, how do you mean exactly? they get rusty inside, or? Will they physically pump water?

What if I run water, and each time before I put it to rest I flush the water out with diesel, let it sit in the unused state with diesel so it doesn't rust up?

The clearances in a diesel injector pump are very fine and water is not a very good lubricant, the pump will most likely seize up, and even if it doesn't it will very quickly corrode and then fail.

 

[Lo-Fi]

A very large, open vat of something vaguely flammable in a workshop seems insane. Adding a device that will successfully atomise it at extreme pressure doing a job that's going to generate heat seems doubly insane. Atomised oil ignites very readily.

At very best you're going to get a sticky mess over everything in the immediate vicinity and probably cause a health hazard requiring breathing gear while operating. At worst a very large fire that's quite challenging to put out.

I'm the first to applaud original thinking, but this is destined to end badly if pursued. Water is ideal - as has already been explorer - because other than the pressure its built up to, its about as safe and stable as it gets.

Another safety concern is oil being blasted through skin at high pressure. It's a very nasty injury and can easily lead to sepsis and amputation. Anything high pressure - even air - blasted at a body part is no laughing matter, but oil is particularly nasty as there's really no biological mechanism to break it down and clear it. One wrong move or a failure of pipework and you're in a bad situation. We all know what it's like when developing something and tinkering...

Regrading water in a diesel pump: Diesel is actually quite a good lubricant. A small amount of anything else - even petrol - will trash an injector pump very quickly. I've swapped a fair few that have suffered from water or incorrect fuel. Your best bet is to find a commercial water jet setup second hand, but again: please be super careful if you're going to play with super high pressure fluids of any kind! There's very real danger of quite serious injury in what might otherwise seem a non-obvious way. You're well into the realms of needing properly rated pipes and crimped connections; it's not the kind of stuff you can throw together in a shed with jubilee clips.

That all being said: it would be really cool to find a viable and affordable cutting head that could be mounted on a DIY CNC table.