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Comment by Steel_Phoenix | Hacker News Reader

Waterjet operator for about a decade here (OMAX). The nozzle slowly and unevenly wears until such a point as you decide it's hurt precision enough that you want to replace it. Everything else on the machine wears out in sudden and near random fashion. Replacing pump parts is done more just because if anything in there fails, you end up with something catastrophic failing. The regularly replaced pump parts are mostly just little gaskets and fittings, but they're pricey anyway. With 50k PSI going through little stainless pipes, sometimes something gets cracked, at which point you get fog shooting across a room out of a hole so small you can't find it with a microscope. Most failures besides the nozzle end up destroying at least three parts. I'm not sure how much of this would hold true at the much lower pressure used here.

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Thank you for your insights.

Going a little off topic here: The failure mode you described reminded me of the horrible accidents that sometimes happen while maintaining high pressure oil systems in industrial machines. The smaller the hole, the worse the incident - human flesh and skin does not pair well with a thin, high pressure stream of fluid. I spare others the details, it's not pretty.

Do you think that a 'personal waterjet' poses more dangers to the operator than machines like a band saw or drill press?

Same danger. A personal water jet will cut your finger off just like a bandsaw. If it can cut metal, it can certainly cut YOU!

I tried to avoid painting a mental picture. I'm not talking about cutting here but rather the things that happen when fluid is injected under your skin and into your body.

Amputation of extremities is not the worst case scenario :-/

Well, when I see someone using a bandsaw, they're usually running a piece of wood through it with their hands near the blade. Cuts seem relatively likely, severity seems moderate.

With a waterjet like the one I use, you would generally have a computer moving the nozzle and not even have a reason to be near the nozzle. It also sounds like a jet taking off. I seem to remember the water speed being something like mach 3 exiting the nozzle, but don't trust my math on that. Cutting is done under water most of the time, which muffles most of the sound and splashback.

On the other hand, I carry a card that tells medical professionals how to treat me if I arrive with a waterjet injury. Waterjets don't work great on laminated materials, because when they hit a transition between materials, they tend to send their energy horizontally. This is also true if it goes through skin and hits bone. It basically shoots you up with water, air, and abrasive, which travels along or in your bones. I've never even come close to injuring myself with the nozzle, but it would absolutely be more scary than a bandsaw.

The closest I've come to injury was one day when I felt an eerie sensation of wind on my skin. I grabbed a piece of paper and tracked it down to a 1/4" stainless water line. I backed away and ten seconds later it was a white cone of fog from a leak that was visible for about 15 feet without even feeling wet. The moral of the story is don't feel around for leaks.

I heard stories about injuries you can get from high pressure leaks from hydraulics guys. By all accounts they absolutely horrifying. They would have their flesh detached from their bones and oil basically soaking into their flesh so that it becomes necrotic later on. Plus they're said not to hurt immediately, doesn't help with treatment. Makes me glad I don't work on hydraulics that's for sure.

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