# Why waterjet? Why not OILjet?



## strantor (May 23, 2020)

Building a DIY/hobbyist waterjet table has long been a dream of mine. I'll get obsessed with it and stay up late for a week straight looking at high pressure pumps and whatnot, then drop it, and a few months later, back for more. There are some pressure washer pumps out there that would do for a very light duty machine but above about 5,000PSI there isn't a whole lot more available as far as water pumps go, until you get into the 60kPSI pumps that are designed for commercial jet cutting operations.

I've tossed around the idea of using hydraulic pumps though, there would be some modifications required and/or dramatically reduced life expectancy pumping water through them instead of oil. Then for the first time today I asked myself, why try to pump water through them? Why not just pump oil? There are some very low viscosity oils out there now. Many newer cars use 0W-20 oil which feels like water on the skin. I don't see why that couldn't carry garnet and work just as well as water. I googled, could find no evidence to the existence of, or discussion about high pressure oiljet cutting. 

Usually when I have a hairbrained idea, I google, and confirmation of the idea manifests itself as such:
- great idea: Someone patented it 75 years ago and it's been for sale ever since; I just never heard of it. I came up the idea on my own, too late.
- good/"ok" idea: someone patented it 75 years ago and it worked as advertised but didn't sell well (or sell for long) because a better solution exists (or came along shortly after).
- bad idea: some dingus tries it every 10 or 20 years and blows his thumbs or testicles off and it makes the news, a paper trail of documentation of just how bad this idea is.
- red flag: google results are nil. Crickets chirping. Either there is in fact at least one new idea under the sun (we all know that's not true) or the idea is so terrible that not even an idiot ever attempted it.

That's where I'm at: red flag. If using oil was feasible then wouldn't waterjet manufacturers be making oiljet machines instead of waterjet machines? everything would be simpler. No stainless/special metals/special seals/etc. A high pressure hydraulic pump is all you need. Too simple. There must be a "gotcha" that's obvious to everyone but me. What is it?

I know 0W oil is expensive. A commercial waterjet tank full to the brim with 0W oil would probably be worth more in oil than in hardware. But there's no reason the entire tank has to be full of oil. The tank could still be full of water, just have a layer of oil that rides on top, and a skimmer/separator to strip it off and feed it back to the pump.


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## Cheeseking (May 23, 2020)

Interesting idea to spit ball over but no. Even 0W is way too viscous. The cost for the volume of oil required even for only a top layer so to speak would be huge. Never mind the difficulties trying to keep it from foaming and separating it from the water. The mist generated would be gawd awful also. Oil film on everything including the floor walls, people just everything. 

Check out on google a company called Wazer. Better route if you want to WJet on a budget. 

(Btw this is 15 yrs being involved with waterjets talking)


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## pdentrem (May 23, 2020)

Oil spray containment would be my concern. Fine atomized oil mist will be inflammable!


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## strantor (May 23, 2020)

Well, there you go; Aerosolized/atomized oil mist creating an explosive atmosphere and unsanitary environment. Pretty good reason not to do it. 

I've seen the Wazer. It has a poly lid that keeps all the water mist contained in the unit. Think a similar approach to an oiljet could work? A 55gal drum of 0w20 oil can be had for under $1k. That seems like plenty for a machine the size of a Wazer ($7k).


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## Tim9 (May 23, 2020)

Other than fire hazards....which I’m sure is a possibility at higher pressures, kerosene would be a better viscosity. But, I’m guessing that once you get to a certain pressure then there’s a strong possibility of self instant combustion. That’s probably why they use water. Why not just use antifreeze....ethylene glycol. No rust there and somewhat better lubricant characteristics for the pump.


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## strantor (May 23, 2020)

Cheeseking said:


> (Btw this is 15 yrs being involved with waterjets talking)


I'm going to keep asking questions; it's what I do. Please don't take it as a challenge to your experience.



Cheeseking said:


> Even 0W is way too viscous.



I did some looking and some math.
Viscosity of water:



viscosity of 0W30 (couldn't find data for 0w20):






So yeah, even if we heat the oil to the boiling point of water, it's still 10X more viscous than water at room temperature. But does that matter? Since (to my limited knowledge) waterjet cutting has only ever been about water, whose viscosity is well known and understood, do we know what effect viscosity has? I didn't even know water's viscosity varied with temperature, except for when it turns to ice. Do you experience viscosity-related problems with cold water? If so, what's the solution? Could the same solution be extrapolated further to allow oil as transport medium? Could it be as simple as a different sized nozzle/orifice?


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## strantor (May 23, 2020)

Tim9 said:


> Other than fire hazards....which I’m sure is a possibility at higher pressures, kerosene would be a better viscosity. But, I’m guessing that once you get to a certain pressure then there’s a strong possibility of self instant combustion. That’s probably why they use water. Why not just use antifreeze....ethylene glycol. No rust there and somewhat better lubricant characteristics for the pump.



Good suggestions. Here they are in some context:
[source]



Kerosene being only twice as viscous as water I think is the better one. I don't think auto ignition would be a problem in the absence of air, would it? I mean diesel auto-ignites from compression in an engine, but only with a very specific air:fuel ration. Kerosene is however quite smelly. I had a leaky bottle behind my shelves once in my garage and just a few drips per hour was enough to make the place feel unhealthy.


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## Cheeseking (May 23, 2020)

No worries I didnt mean to sound as if Im the authority by no means just that I do have some background/ experience running one and dealing with the vagaries of the process. It’s definitely harsh and unforgiving even with ideal conditions and maintenance. Im all for out of the box ideas. I’m king of crazy sometimes so no worries I challenge my own ideas to death trying to poke holes in them. I may have missed the reason you’re wanting to use oil vs water. Is it due to corrosion of the parts or machine???


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## eugene13 (May 23, 2020)

What about super critical CO2? other than it could suffocate you.


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## Cheeseking (May 23, 2020)

We have used dry ice as a blasting media to remove mold coatings from permanent molds for aluminum casting. The idea is it “evaporates” and doesn’t leave a mess like shot blasting with sand, walnut shell or steel shot does. Might work but would require a ton of compressed air flow$$$


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## strantor (May 23, 2020)

Cheeseking said:


> I may have missed the reason you’re wanting to use oil vs water. Is it due to corrosion of the parts or machine???


Being a DIY machine, it would be made mostly from the cheapest off-the-shelf components available. The pump would likely be a repurposed pump, originally designed & sold for purposes other than waterjet cutting. Pressure washer pumps get me to about 4,500 PSI but if I want to go higher than that, all I find are hydraulic (oil) pumps. So say I find a 10kPSI hydraulic pump, is it better to reinvent the pump to move water without prematurely failing, or is it better to reinvent the process to use oil instead of water? The second half of that question is what I'm exploring.


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## markba633csi (May 23, 2020)

Flammable or inflammable? Are they the same thing? LOL  Sounds like a George Carlin routine-  "down the tubes!"  What tubes?


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## kd4gij (May 23, 2020)

Oil is a lubricate and would not be efficient at cutting.  And a high pressure hydraulic pump needs the heavy weight oil to achieve the pressure.


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## Cheeseking (May 23, 2020)

Guys the water in most cases is not doing the actual cutting. Abrasive media (garnet) is entrained in the stream in the cutting head, post orifice, before it enters the silicon carbide mixing tube. The sharp garnet particles are what cuts the material. That said many softer materials like rubber can be cut water only.


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## pdentrem (May 23, 2020)

*Flammable and inflammable* do not mean the same thing. If something is *flammable it *means it can be set fire to, such as a piece of wood. However, *inflammable* means that a substance is capable of bursting into flames without the need for any ignition. ... The opposite of both words is non-*flammable*.


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## Mitch Alsup (May 23, 2020)

eugene13 said:


> What about super critical CO2? other than it could suffocate you.



How did you enjoy the play, Mrs. Lincoln ?


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## rwm (May 23, 2020)

Why do you think oil would have such and advantage? It is not particularly difficult to design a waterjet using water. Stainless hardware is not ridiculously more expensive than regular steel when building from scratch. I guess for a hobbyist, trying to adapt a hydraulic pump it might make some sense but for industry, no. BTW there are lots of low viscosity organic fluids you could try other than conventional oils. As discussed, flammability is the major issue. I suppose you could go with PCBs but I would not recommend it! I can just imagine aerosolized PCB all over the shop.
Why don't you try using a hydraulic pump to pump water with a corrosion inhibitor? Think water soluble coolant.
Robert


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## BtoVin83 (May 23, 2020)

Cheeseking said:


> Guys the water in most cases is not doing the actual cutting.


Not necessarily, we did downhole under reaming using plain water at 10,000 psi. It would cut through rock concrete and steel with no problem. One time the nozzle got stuck in the whipstock and cut the whole end of the whipstock off.


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## strantor (May 24, 2020)

rwm said:


> Why do you think oil would have such and advantage? It is not particularly difficult to design a waterjet using water. Stainless hardware is not ridiculously more expensive than regular steel when building from scratch. I guess for a hobbyist, trying to adapt a hydraulic pump it might make some sense but for industry, no. BTW there are lots of low viscosity organic fluids you could try other than conventional oils. As discussed, flammability is the major issue. I suppose you could go with PCBs but I would not recommend it! I can just imagine aerosolized PCB all over the shop.
> Why don't you try using a hydraulic pump to pump water with a corrosion inhibitor? Think water soluble coolant.
> Robert


It isn't just rust that worries me. It's my understanding that hydraulic pumps are lubricated by the oil flowing through them. I believe hydraulic pumps often have metal-on-metal moving parts in areas where a water pump would have metal-on-seal or metal-on-bushing. And further it's my understanding that waterjet pumps are so expensive because of the special seals and bushings required; seals and bushings that a hydraulic pump doesn't have, and doesn't need.

[My understanding] could be way off.


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## strantor (May 24, 2020)

eugene13 said:


> What about super critical CO2? other than it could suffocate you.


Interesting stuff, never heard of it.


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## middle.road (May 24, 2020)

Keep an eye on the auctions. There was one last fall that had two of them in it. Can't remember what price they for though.
I last saw the process in action back in the 90s - it was fascinating and a lot cheaper that CNCing out the shapes needed, and the tolerances they could hold were insane.


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## matthewsx (May 24, 2020)

Yeah, definitely an item to pick up cheap at auction rather than try to engineer ones self. You definitely don't want to blow your thumbs off....

John


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## Ulma Doctor (May 24, 2020)

they use water-jets for cutting frozen meat products on the industrial level

there was an occasion that happened at a trade show where a spectator swiped his finger under the demonstration stream of cutting water, like he would a stream of water coming from the sink.
he lost a finger


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## Twirpunky (May 24, 2020)

Kind of off topic but interesting.
       In an engineering department where I work, they were developing food processing water jets. The one I recall them working on was for pickles. The pickle would shoot down a tube like a gun barrel and pass through three jets that would cut the pickle into six wedges and pack them in a jar.  
   I see pickles in jars like that all the time and had never given a thought to how they were produced. 

  Another one they were working on was a chicken nugget slicer right off the chicken. 


D


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## middle.road (May 24, 2020)

Dang, I'm flinching at that one just thinking about it and the time I stupidly put my hand in the way of the pressure washer @2400psi.
*CRINGE*


Ulma Doctor said:


> they use water-jets for cutting frozen meat products on the industrial level
> 
> there was an occasion that happened at a trade show where a spectator swiped his finger under the demonstration stream of cutting water, like he would a stream of water coming from the sink.
> he lost a finger


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## Cheeseking (May 24, 2020)

Yes all kinds of food and even diapers are cut with water only. 
We cut all kinds of crazy stuff with ours.
IT guys periodically give us old hard drives and we line them up, slice them in half before tossing them. Its weird they actually feel hot afterwards.


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## rwm (May 25, 2020)

Just to back track a little I assume you saw the guy who build the waterjet out of a pressure washer? He was cutting aluminum up to maybe 1/8" using garrnet.
RWM

OK-Thinner maybe 1/16"


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## Downunder Bob (May 25, 2020)

If you really want to use oil How about diesel fuel,it's very low viscosity, but does have some lubricating properties. You could also put together a couple of diesel fuel pumps they put out a pretty high pressure, and don't wear out very quickly.


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## strantor (May 25, 2020)

Downunder Bob said:


> If you really want to use oil How about diesel fuel,it's very low viscosity, but does have some lubricating properties. You could also put together a couple of diesel fuel pumps they put out a pretty high pressure, and don't wear out very quickly.


That's something I'll devote some time to investigate. Never thought of using diesel, or diesel injection pumps. I would rather use water than diesel (smell) but the diesel pump is a high pressure pump I never thought to look into. It seems it will not be so easy to get specs. I've briefly looked and did not see any flow/pressure data listed for any of the injection pumps that I pulled up from various websites. I assume flow will be very low and many pumps in parallel would be needed.


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## strantor (May 25, 2020)

rwm said:


> Just to back track a little I assume you saw the guy who build the waterjet out of a pressure washer? He was cutting aluminum up to maybe 1/8" using garrnet.
> RWM
> 
> OK-Thinner maybe 1/16"


Yes I've seen that. It "works" but I would not consider that performance acceptable for what I want to build. I would consider the performance of the wazer to be just below bar for my taste. If I could get somewhere between wazer and an entry level industrial machine that would be perfect. This is why I have mostly ruled out pressure washer pumps. Maybe there is a way to modify a pressure washer pump to achieve 10k+PSI without risk life, thumbs, or testicles? If so I would gladly hear of it.


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## Downunder Bob (May 25, 2020)

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.


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## strantor (May 25, 2020)

Downunder Bob said:


> 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?


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## MontanaLon (May 25, 2020)

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.


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## matthewsx (May 25, 2020)

strantor said:


> 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.
> ...



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


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## strantor (May 25, 2020)

MontanaLon said:


> 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:



Tim9 said:


> 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


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## strantor (May 25, 2020)

matthewsx said:


> 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!



matthewsx said:


> [...]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:


matthewsx said:


> 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?


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## strantor (May 25, 2020)

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.


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## brino (May 26, 2020)

@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:



strantor said:


> 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


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## Downunder Bob (May 26, 2020)

strantor said:


> 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.
> ...



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.


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## Lo-Fi (May 26, 2020)

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.


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## strantor (May 26, 2020)

Lo-Fi said:


> 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.


Point taken. Oil is off the table. I have no intention of creating an explosive atmosphere. 



Lo-Fi said:


> 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...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.


I appreciate you taking the time to acknowledge the safety aspect. Too often it is assumed the dangers are known. In this case however, they are. I served aboard a submarine and part of my training was dealing with extreme pressure fluids & gasses. I've seen the grotesque pictures of what happens. I understand the difference between high pressure lines & fittings, and not. If I go forward with this and post something that someone else might try to emulate, I will be sure to highlight the safe way of doing it.


Lo-Fi said:


> 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.





Downunder Bob said:


> 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.


What about adding some water soluble CNC cutting fluid concentrate to the water? That might provide some supplemental lubrication that might be missing from the glycol mix. I imagine it might take some empirical discovery (and a few destroyed pumps) to get the mix right, if it works at all.


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## Lo-Fi (May 26, 2020)

Cool, that's what I was getting at: it's not just your safety, but potentially others on an open forum. Sounds like you've got a good handle on it yourself, which is great to hear. 

Try it, but I don't think you'll have much reliable success with a diesel pump. They're designed for a fluid with specific properties, after all. A small amount of water, a couple of minutes pumping petrol and they're shot. Your best bet would be a real crude old tractor pump or suchlike. The older the better. Anything modern is going to stick two fingers up at you very quickly! 

What are you intending to use as a jet/orifice?


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## strantor (May 26, 2020)

Lo-Fi said:


> Cool, that's what I was getting at: it's not just your safety, but potentially others on an open forum. Sounds like you've got a good handle on it yourself, which is great to hear.
> 
> Try it, but I don't think you'll have much reliable success with a diesel pump. They're designed for a fluid with specific properties, after all. A small amount of water, a couple of minutes pumping petrol and they're shot. Your best bet would be a real crude old tractor pump or suchlike. The older the better. Anything modern is going to stick two fingers up at you very quickly!
> 
> What are you intending to use as a jet/orifice?


The business end will be commercial waterjet parts. Those are actually affordable. There was a video linked earlier in this thread; if you watch all the videos in that series you'll get an idea how I plan to do this. He's using a pressure washer as his prime mover but I intend to use something with a bit bigger cojones. Maybe diesel pump or maybe I need to build a high pressure triplex pump from scratch? I hope not. The older diesel pumps I believe are not so high pressure. Maybe 5kPSI? 10k? It's my understanding that 20k+PSI fuel pumps are relatively new on the scene.


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## whitmore (May 26, 2020)

strantor said:


> Building a DIY/hobbyist waterjet table has long been a dream of mine. ...
> 
> I've tossed around the idea of using hydraulic pumps though, there would be some modifications required and/or dramatically reduced life expectancy pumping water through them instead of oil. Then for the first time today I asked myself, why try to pump water through them? Why not just pump oil?



One reason not yet mentioned: water is denser than oil.   Once the jet is created, it carries grit (and hammers it into the cut) using
the momentum of a fast stream of mass.   You get more mass into a narrow kerf with the denser liquid.


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## Cheeseking (May 26, 2020)

A commercial cutting head with high pressure on off valve and mini hopper will absolutely not be cheap. The Silicon carbide mixing tubes are $230 ish each and a consumable.
I have a box of used up WJ parts sitting here and the amount of money it represents is staggering.
Have you researched the cost and availability on home use qty abrasive? Garnet abrasive is anywhere from $0.25/lb to $.50. This is a serious rabbit hole heading down.


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## strantor (May 26, 2020)

Cheeseking said:


> A commercial cutting head with high pressure on off valve and mini hopper will absolutely not be cheap. The Silicon carbide mixing tubes are $230 ish each and a consumable.
> I have a box of used up WJ parts sitting here and the amount of money it represents is staggering.
> Have you researched the cost and availability on home use qty abrasive? Garnet abrasive is anywhere from $0.25/lb to $.50. This is a serious rabbit hole heading down.


I have looked into the costs of all the needed components and consumables but that was years ago. I confess I don't have a bill of materials for this or even a ballpark figure of what it will cost, but at one point I did, and I deemed it worth pursuing. Back then it wasn't until I got to the pump that i started to get sticker shock, and the pump is what I've been fixated on ever since. There's no room in my mind for price of garnet and valves until I find a cost effective pumping solution. Gotta start somewhere, I choose right here.


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## Cheeseking (May 26, 2020)

BtoVin83 said:


> Not necessarily, we did downhole under reaming using plain water at 10,000 psi. It would cut through rock concrete and steel with no problem. One time the nozzle got stuck in the whipstock and cut the whole end of the whipstock off.



I don’t doubt that that happened In fracking or oil rigging orwhatever you were doing. Rock and clay is much easier than metal. It likely ate thru the rock because of the loose particles stirred up by the jet of water and possibly via water only on some of the softer formations. Same with the steel whipstock whatever that is. The steel was cut because of the particles of rock an minerals along with that 10k stream of water in a confined space. You try to cut steel plate with only water good luck. It may eventually cut but will take forever. And ever. Even at that whats doing the cutting is the dissolved solids in the water. If we ever run out of abrasive or have a clog while cutting theres no mistaking that piercing sound and the huge rooster tail spray and mist cloud. Not cutting. 
But yes theres plenty of materials that can be cut water only. 
In fact the OP will probably have the best chance of success with a water only system cutting wood etc. maybe then advance to add abrasive capability. Lol we do like to call ours the squirt gun.


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## Downunder Bob (May 27, 2020)

strantor said:


> Point taken. Oil is off the table. I have no intention of creating an explosive atmosphere.
> 
> 
> I appreciate you taking the time to acknowledge the safety aspect. Too often it is assumed the dangers are known. In this case however, they are. I served aboard a submarine and part of my training was dealing with extreme pressure fluids & gasses. I've seen the grotesque pictures of what happens. I understand the difference between high pressure lines & fittings, and not. If I go forward with this and post something that someone else might try to emulate, I will be sure to highlight the safe way of doing it.
> ...



Certainly I would not put anything into a diesel injector pump other than very clean diesel. As has been said a small amount of water or even petrol will wreck it beyond repair. Ask any long haul truck driver why they are fanatical about filters.

I'm not convinced that using diesel is as dangerous as has been suggested,I have worked at an injector testing bench for large marine diesels. 15000HP, And have been surrounded by a fine mist of diesel with other smoking nearby and nothing ever happened. Diesel has to be atomised into very hot air to ignite. 

As an added precaution if you were to use your cutting device in an enclosure the atmosphere would be far too rich to ignite, even with a good source of ignition


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## Joe in Oz (May 28, 2020)

I think the key part of a WJ "pump" has not been mentioned yet: the pressure intensifiers.


			https://cdn.thefabricator.com/a/6-tips-for-troubleshooting-your-waterjet-1527790029.jpg
		

The pump part of a WJ system actually doesn't produce such enormous pressure. That pressurized water is fed into intensifiers which are also water pressure operated. (Note: There are also hydraulically driven intensifiers using oil hydraulics. see here: https://www.performancewaterjet.com.au/assets/components/phpthumbof/cache/WATERJET CUTTING ILLUSTRATION2.cf4fe5b245def2cd59e80688eb33c466.jpg)
They are effectively a large hydraulic ram, pushing a very small piston in it's small cylinder. The piston then produces a VERY much higher pressure, but at a small flow rate. These amplifiers are usually double ended - and often more than one. That's how the pulses from each stroke are quite close together. These intensifiers also cycle quite slowly, relatively speaking. You may be able to build an intensifier and drive it with a decent sized gas or diesel pressure washer (lets say 13Hp) that makes - say 5000PSI at 6 Gal/min. The amplifier would multiply that by say 6:1 to give you 30,000PSI at 0.5 gal/min, the remaining water is used to drive the intensifier.
The critical thing is precision lapping of the cylinders and pistons, and as far as I know there are no seals as such involved, since the leakage just goes back into the driving cylinder to be recycled....
I'm watching your "team" and your thought processes with great interest!
For what it's worth, I have used WJ cutters. 
I also have a 4800PSI 13Hp pressure washer and I use it with recycled glass grit for wet sand blasting. I tried garnet, but it is too expensive and not quite as effective as the very sharp edged glass grit. Oh, and the glass looks like ordinary sand once it has dried in my driveway  The thought of trying to cut something with the stream - using a waterjet nozzle) has occurred to me quuite a few times....


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## rwm (May 28, 2020)

BTW- Ward waterjet has a nice overview of the technology:









						Waterjet University - Pumps
					

Waterjet cutting is made possible by pressurizing water to very high pressure (50,000+ psi). This is accomplished with the use of pumps of various designs.




					wardjet.com
				




Robert


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## Cheeseking (May 28, 2020)

Joe OZ thats correct. There are 2 main types of WJ pumps. Intensifier and Direct Drive (piston). We have One company I know of uses a servo driven intensifier which we are actually considering going to but most are hydraulic driven. One issue with the hydraulics is waste heat generated maintaining pressure while not cutting. There are many issues with home brew WJ we have not yet unpacked in this discussion but one at a time lets do it.


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## Joe in Oz (May 29, 2020)

Thanks for the link.
I read about servo drive intensifiers. Very interesting machines. They sound like a very efficient way of pumping high pressure without generating much waste heat and simplifying the entire mechanical side of the system.
Linear servos are still very expensive, bit I saw one rotary servo driving the pistons with a ballscrew. That seems almost feasible for a DIY pump 

Cheers
Joe


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## e189552 (May 29, 2020)

The original design concept for waterjet cutting was a large tube/barrel filled with water. A large extremely heavy piston was then lowered into it.


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## hman (Jun 1, 2020)

I haven't seen this mentioned yet ... but as I recall from a visit to a commercial machine shop, only pure "virgin" water is fed into the pump of a waterjet cutter.  They do NOT recirculate/filter/treat used water.  This makes a lot of sense, because the extremely fine clearances in the pumps would require some kind of "ultra" filtration of the water.  And in general, the finer the filter, the slower the flow through it, and the more frequently it would clog or require cleaning.

So using any kind of oil or similar substance would not only involve the cost of what's collected in the tank, but also a steady supply of new/clean oil to feed the jet.  And as has been pointed out, oil is a lot more expensive than water.  So operating costs would become a major consideration.


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## rwm (Jun 1, 2020)

According to the applied science video the cutting head parts were pretty cheap. He talks about the price of the orifice specifically.
Robert


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## 7milesup (Jun 1, 2020)

Ethylene Glycol is also flammable.  Or is that inflammable.  Well, it can ignite/burn anyhow.  Pulling tractors inject ethylene glycol to increase HP.

Strantor...  My brother has been a diesel injector pump specialist for 40 years.  If you have specific questions I could run it past him.


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