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bry1975:
Hi chaps,

With the pump I used in the past the hydraulic hose is very thin like less than 10mm diameter, I will speak to the firms that produce the 10,000psi hand pumps and get advice from them and with regards the chamber fasteners I will be looking at using Grade 12.9 diameter M16 and probably 6 of them for plenty of overbuild.

Bry

David Jupp:
550 bar isn't ridiculously high pressure, but a bolted joint will need some serious pre-load to work well.

Materials - should be fairly strong, but not at the expense of toughness; fatigue is always your worst enemy - Low alloy steels are quite common, also some stainless steels. Soluble oil/water makes a good test fluid - it's kind on pump seals, and has anti-corrosion properties (can smell a bit if left to stand and the bug killers get used up).

Clamps or a threaded barrel are common instead of bolts for the closure at higher pressures, also sealing on the bore rather than the end of the chamber will be more forgiving. There are several detail options. An O ring (with suitable back-up ring) can be made to work, there are other options, though more costly.

Fluid connection - stainless capillary tubing is probably simplest at very high pressures, there are compression fittings available, or it can be brazed.

Standard design formlae aren't used at higher pressures - stresses are nothing like uniform through the vessel wall. There are a few design codes that are applicable. Use a minimum design factor of 2 x MAWP, testing should be to roughly 1.5 x MAWP.

May sound 'soft' but you should draw up an inspection schedule for such a chamber as it sounds like it will be pressure cycled regularly. I haven't looked for viewing ports at that pressure for a hwhile, they should be available in saphire.

bry1975:
I have thought about having the whole chamber face covered with gasket sheet probably better than just relying on an o ring in a groove.

Thanks David.

mike os:

--- Quote from: AdeV on May 23, 2011, 08:39:15 AM ---
--- Quote from: mike os on May 23, 2011, 05:12:09 AM ---So basically the rating ie either a lie or a con?... or both? :bugeye:

--- End quote ---

No, but you could say it was misleading.... a 30 metre watch would presumably pass a 30 metre static test (i.e. using a chamber, like the ones shown on this thread); but if you dived into a swimming pool with it, it's quite possible that the dynamic pressure (i.e. the instant pressure as it hits the water) could be significantly higher than the 30 mtr pressure.

As an example; consider when you drop something. It accelerates at 1G; but when it hits the floor; depending on how much the floor & obect deform, it could be decelerating at a rate in excess of 1000G, which is why so much stuff breaks when you drop it.

--- End quote ---

misleading = lying

if its a divers watch & you cannot dive in it to its rated depth it is not fit for puropse.... so still a con :headbang:

David Jupp:
Conventional gaskets are a big ask at 550 bar. The more gasket area, the tighter the bolts have to be so that pressure in the gasket material remains greater than in the fluid.

O rings can work successfully to a few thousand bar - if the detail of the joint is right (but don't expect to re-use them many times). Typically you need line contact (lens rings, cone rings etc) and a fair bit of pre-load, or some kind of pressure activated seal (Bridgman, O ring, wave ring, Grayloc).

For simplicity, a plug which protrudes into the end of the bore with a groove round it for an O ring and a back-up ring is probably the way to go. Within reason you don't need to worry too much about bolt stretch as the plug can move axially a bit and the O ring will still seal.

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