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Comment by noonespecial | Hacker News Reader

Odd that they don't want to let anyone know the operating pressure. They seemed to spend an inordinate amount of song-and-dance dodging the "whats the pressure" question.

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It is odd. That was my first question, having used a more traditional (==much larger) one.

I have trouble figuring how the cutting speeds claimed jibe with the overall weight of the device. Not calling it out, just saying based on their numbers, that seems like quite a lightweight tank for the kind of pressure used for cutting, for instance, stainless steel.

I'm also kinda wildly interested how they keep vibration down, given the operating pressure, etc

I wouldn't be surprised if its what a standard pressure washer can do (3k PSI) as they claim to use parts from "other industries".

I doubt the pressures are much above 10k PSI as there isn't the power to generate those pressures with a reasonable flow from a standard US outlet.

Using gpm=(hp x 1715 x efficiency)/psi and allowing for 90% pump efficiency along with max 1.93 hp continuous from a 15A 120VAC receptacle, we can simplify the pumping-water-with-a-North-American-receptacle equation to gpm=3000/psi. So 10k psi outputs only 0.3 gpm, 3000psi outputs 1gpm, and 2000psi spits out 1.5 gpm (the latter of which matches the output from the top electric pressure washers).

And since they said that it uses 10-20% the water of a standard shower head...

A modern shower head uses about 2gpm, so we are talking about 0.2 to 0.4gpm. That would give us a pressure of about 7500 to 15000psi using your equation.

This is much more realistic. 3k psi will struggle to cut a cake.

As someone used to metric, this is probably the msot confusing comment chain I've read yet o.O

You don't measure cutting force in cakes?

For those that need it in metric, a cake is roughly equivalent to a scone...

At least in the UK, Her Majesties Customs and Excise tried to measure it in biscuits (which require 17.5% greater cutting force than cakes), but Mcvities prevailed in the courts.

We measure cutting force using a very old baguette held at the Bureau international des poids et mesures.

That sounds like the worst case to me. They are doing their demos with 7500 psi from an outboard pump and thinking that it's going to be a minor detail that can be worked out after the kickstarter succeeds to generate a workable pressure from 15A 120v.

If they told us the pressure they're using for their demos, some smarty with a slide-rule might call them on getting that from a normal wall outlet.

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