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    Re: Sextant AN 5851-1
    From: Robert Eno
    Date: 2004 Jun 3, 09:04 +0100

    Hello Mr. Henry,
    Given the situation as you describe it, the bubble chamber needs to be
    topped up with some fluid. I can only hazard a guess at to what fluid the
    Navy Mark V uses, however, I can tell you that the Plath and the RAE MK
    IX used hexane or pentane as a bubble chamber fluid. Kerosene or a
    kerosene-like fluid was also commonly used in some bubble sextants,
    although I tried using this stuff in my Plath and found it to be too
    viscous. Suggest you try hexane first, but ensure that the material used
    for sealing the bubble chamber is compatible with hexane.
    It is too bad that my friend John Luykx is no longer with us for he would
    have had the answer to your question without pondering.
    As for storage, it is very important to return the bubble adjustment knob
    to the neutral position as the bubble is formed and removed by exerting
    pressure on a bellows or diaphragm. Like all spring-loaded devices, it is
    always best to store it in the "relaxed" mode.
    I believe the diaphragm on the Mark V is made out of metal (but don't
    quote me on that) so it is more likely that the seal has dried up and
    cracked. You may have to operate on the patient Dr. Henry ;-^)
    Hope this helps. Perhaps one of our more knowledgable folks (Ken Gebhart
    comes to mind) may have better answers.
    >I have a Navy Mark V (AN 5851-1) sextant which I purchased last winter
    >have been using occasional.  When I purchased the sextant it had not been
    >used for a very long time I removed all of the housing and cleaned it in
    >it's entirety.  The bubble on recite was very large and unadjustable but
    >with the replacement of the o ring at the thimble pressure pump and
    >persistent attempts at using it I was able to get the bubble to adjust
    >large to small and back.  I would also like to note that since I a have
    >received the instrument I has had a distinct sent which could be the
    >fluid and that the I have stored it with this loose per a note typed on a
    >piece of paper in the box which reads as follows. " Important, Always
    >bubble control nut to neutral when not using the instrument. (nut should
    >spin freely) Leaving pressure on diaphragm damages bubble unit beyond
    >Recently I took the unit out of it's case for the first time in a month
    >the bubble is back to it's large size and I am not able to reduce it.  I
    >wondering of the fluid needs to be refilled. If so what is the fluid and
    >where does one get the fluid and how is refilling it accomplished?  Is
    >diaphragm damaged? If it is how can I repair or replace it?  I would
    >appreciate any questions and assistance that one might give me.
    >Peter Henry
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