[BITList] more Nuclear submarines went to seawithpotentiallydisastrous defect | UK news | The Guardian

[HUGH]

Colin,

I make 400 psi about 27 bar, around 650 feet water head.  From a website :

The Crosby Style HB-BP is designed specifically to meet the exacting requirements of nuclear power plant applications where the valve is not allowed to discharge to the atmosphere. The bellows "balances out" the effects of high backpressure in the discharge system, assuring constant popping pressure despite variable backpressure, Crosby's patented eductor design controls the dynamic forces of discharging fluid to stabilize valve performance. The valve provides full capacity, stable operation at backpressure up to 50% of the set pressure.  http://www.crosbynuclear.com/Crosby.asp

They quote up to 172 bar as settings. The bit I've underlined is ambiguous - the rest is advertising gobbledegook at the moment.  The effects of high back pressure cannot be "balanced out" - the valve setting doesn't change, nor does the external pressure. I think they are talking about a variety of the standard dodge whereby a diaphragm with differential areas above and below regulates pressure.  The bellows is a hardier version.  Incidentally, 172 bar is about 5900 feet of water head, so that should do for most oceans on earth.

None of this solves the problem of the mysterious hull valves.

Hugh.
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