How can fittings withstand the pressure in a water cutter?

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Discussion Overview

The discussion revolves around the types of fittings and piping that can withstand the extremely high pressures used in water jet cutters, which operate around 5,000 bars (~70,000 psi). Participants explore the materials, designs, and engineering considerations necessary for such high-pressure applications.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • Some participants express amazement at the high pressures involved in water jet cutting and question what materials can withstand such conditions.
  • One participant suggests that the high pressure mentioned may refer to total pressure rather than static pressure, implying that static pressure could be lower.
  • Another participant notes that despite high pressures, the flow rates are low, allowing for the use of smaller, thicker components in the design of fittings.
  • It is mentioned that standard hydraulic fittings are not suitable for water jet applications, and that the cutting tools typically use very hard materials like ruby or diamond.
  • Some participants identify specific manufacturers, such as Autoclave, that produce fittings capable of withstanding pressures up to 150,000 psi.
  • There is a mention of the design of fittings being crucial, with thicker pipes and specialized nozzles made from materials like sapphire or diamond to handle the pressure gradient effectively.
  • One participant describes the conversion of mechanical energy into high kinetic energy of the fluid jet as part of the operational mechanics of water jet cutters.

Areas of Agreement / Disagreement

Participants generally agree that specialized fittings and materials are necessary for high-pressure applications, but there are differing views on the specifics of pressure types and the effectiveness of various materials.

Contextual Notes

There are unresolved assumptions regarding the definitions of total pressure versus static pressure, as well as the specific materials and designs that are optimal for high-pressure fittings.

TSN79
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I've seen some different types of water jet cutters and they are indeed cool :)
I read that these operate in areas around 5 000 bars (~70 000 psi) which is so much I can't even grasp it! But what I wonder is what kind of piping and fittings could even withstand this?? A regular house has water pressure around 5 bars, and leaks appear all the time for a variety of reasons. Is it simply that these cutters are made of fittings and pipes that are the most super duper hardcore of all?
 
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I know nothing about these things, but one thing that comes to mind is the possibility of total pressure vs. static pressure. Chances are, the really really high pressure stated is a total pressure, so to speak. It is the pressure the jet will exert on a solid, after it has been slowed. So, while the total pressure may be really high inside the cutter, the static pressure is probably quite low.
 
Even though the pressures are very high, the flows are very low. The pumps are reciprocating type and the low flow allows the use of very small components and thus can be made as thick as required. You are not going to find your run-of-the-mill hydraulic fittings on the business end of a waterjet or abrasive waterjet. The tool itself is usually ruby, diamond, garnet or some other very hard stone. The mixing tubes are usually the weak link in the chain.
 
TSN79 said:
I've seen some different types of water jet cutters and they are indeed cool :)
I read that these operate in areas around 5 000 bars (~70 000 psi) which is so much I can't even grasp it! But what I wonder is what kind of piping and fittings could even withstand this?? A regular house has water pressure around 5 bars, and leaks appear all the time for a variety of reasons. Is it simply that these cutters are made of fittings and pipes that are the most super duper hardcore of all?

Fittings can be made for really high pressures, just depends on their design. Autoclave is who we use for all of our high pressure applications.

These go up to 150,000 psi:

http://www.autoclave.com/products/fittings_and_tubing/high/high.html

CS
 
As stewart mentions, there are companies that make very high pressure fittings. I can think of 5 different companies that make tubing and fittings that can withstand that pressure. I suspect there are quite a few more.
 
As far as I know, the fittings/pipes are relatively thick to minimize stress at high pressure. The nozzles have inserts made of sapphire or diamond or perhaps boron-nitride. The pressure gradient (drop) through the nozzle fitting is substantial - HP to essentially ambient.

Pressure (mechanical energy) is converted to high kinetic energy of the fluid jet.
 

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