Why waterjet? Why not OILjet?

[strantor]

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.

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.

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.

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.

 

[Lo-Fi]

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?

 

[strantor]

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.

 

[whitmore]

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.

 

[Cheeseking]

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.

 

[strantor]

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.

 

[Cheeseking]

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.

 

[Downunder Bob]

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.



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.

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

 

[Joe in Oz]

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....

 

[rwm]

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