[PSUBS-MAILIST] over pressure valve
Private via Personal_Submersibles
personal_submersibles at psubs.org
Fri Jun 19 17:48:54 EDT 2015
No, it's the other way around - my issue was caused by the motors getting cold. I put the oil in on a hot VA day, it was 90-95 degrees. At depth the water was at 42 degrees, so about a 50 degree difference. Contraction of the oil at depth was greater than the puny 10ml hose volume, and we were beyond the pressure rating of the lip seals so the motor sucked in water. Then upon return to the surface, the air bubble in the motor stored the pressure and pushed oil back out.
Of course you could also have the issue if you fill the motor cold and it gets hot, such as from running it out of the water or something.
> On Jun 19, 2015, at 5:28 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Alec,
> At first I resisted the notion of thermal expansion, but I was thinking in terms of heat generated from motor use. I didn't consider the temperature change from the sun on a black motor until the light went on :-)
> I have changed my p trap ss tube to a larger hose so there is more air volume to work with. I am ready to test that part. Now I have to fix my bent up rudder :-(
> Hank--------------------------------------------
> On Fri, 6/19/15, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Subject: Re: [PSUBS-MAILIST] over pressure valve
> To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
> Received: Friday, June 19, 2015, 5:03 PM
>
> Oh! Well I
> suppose it just depends on the volume the valve can handle.
> This is an interesting calculation, which I have not done
> but should. In general, these valves should handle pretty
> huge flow rates. But you're right, its basic to surface
> very slowly when there's any over-pressure - normally we
> dive with under-pressure. For a K-boat sized hatch, an
> over-pressure of 1/4 psi translates to a force of 95lbs
> trying to pull the dome out of the hatch ring. I know
> Snoopy's dome stays put at 1/4 psi, but I wouldn't
> take it any further than that just in case.
> BTW, on the subject of calculations
> and changing topics back to the recent thruster compensation
> thread, you were right about the temperature change. The
> volume I had to compensate was a combination of thermal
> contraction and air bubble. The air bubble was of unknown
> size, but I ran the numbers on the thermal contraction alone
> and it is enough to cause the problem. The little hose only
> has a an internal volume of 10ml. The thermal contraction of
> the oil turned out to be 16ml - add to that the volume of
> the unknown bubble, and you can see the hose was inadequate
> even if it squashed to zero internal volume. I am now
> installing bellows bottles in place of the little hoses,
> with a capacity of 60ml. And a better filling method that
> should eliminate the bubble. You'd think I wasn't an
> engineer, assuming the effect of thermal contraction to be
> negligible. Its easy to focus the calculations on big items
> like hull strength or stability and make assumptions about
> the little stuff.
> Best,
> Alec
> On Fri, Jun 19, 2015 at
> 4:19 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
> wrote:
>
>
> You have to be experienced to surface slowly and hover while
> the valve leaks out the
> air.--------------------------------------------
>
> On Fri, 6/19/15, Alec Smyth via
> Personal_Submersibles <personal_submersibles at psubs.org>
> wrote:
>
>
>
> Subject: Re: [PSUBS-MAILIST] over pressure valve
>
> To: "Personal Submersibles General Discussion"
> <personal_submersibles at psubs.org>
>
> Received: Friday, June 19, 2015, 4:16 PM
>
>
>
> I
>
> don't get the "in the hands" part... its
>
> completely automatic.
>
> On Fri, Jun 19, 2015 at
>
> 4:09 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
>
> wrote:
>
>
>
>
>
> Agreed,
>
>
>
> In the hands of an experienced submarine operator an
> over
>
> pressure valve is safe, providing it is large enough.
> I
>
> have not seen an example of a large enough OPV. A
> simple
>
> valve in the hatch will do the same job, just need an
>
> umbrella :-)
>
>
>
> The noise of a compressor is a welcome sound if it
> means
>
> keeping the dome on the sub :-)
>
>
>
> Hank--------------------------------------------
>
>
>
> On Fri, 6/19/15, Carsten Standfuß" via
>
> Personal_Submersibles <personal_submersibles at psubs.org>
>
> wrote:
>
>
>
>
>
>
>
> Subject: Re: [PSUBS-MAILIST] over pressure valve
>
>
>
> To: "Personal Submersibles General
> Discussion"
>
> <personal_submersibles at psubs.org>
>
>
>
> Received: Friday, June 19, 2015, 2:47 PM
>
>
>
>
>
>
>
> But a overpressure vale works
>
>
>
> full auto. A compressor
>
>
>
> not.
>
>
>
>
>
>
>
> A OPV needs
>
>
>
> no energy - but a compressor did.
>
>
>
>
>
>
>
>
>
>
>
> A OPV needs no room - but
>
>
>
> a compressor did.
>
>
>
>
>
>
>
> And a
>
>
>
> compressor is
>
>
>
> a noisy solution..
>
>
>
>
>
>
>
> vbr
>
>
>
> Carsten
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> "hank
>
>
>
> pronk via Personal_Submersibles" <personal_submersibles at psubs.org>
>
>
>
> schrieb:
>
>
>
> > Personally I think an onboard
>
>
>
> compressor is a much safer option than an over
> pressure
>
>
>
> valve. There are multiple safety benefits to an
>
> onboard
>
>
>
> compressor, over pressure being the biggy. With a
>
>
>
> compressor you can get rid of the pressure without
>
> surfacing
>
>
>
> and trying to control a perfect ascent. With the
> OPV
>
> you
>
>
>
> have to surface a bit and let air out and wait then
>
> surface
>
>
>
> more and wait and so on. You can't just surface
> and
>
> hope
>
>
>
> the valve keeps up with the demand. This is more
>
> important
>
>
>
> for subs with large domes.
>
>
>
> > The next
>
>
>
> benefit to a compressor is, if you lost all your air,
>
> you
>
>
>
> surface by dropping your weight. In my case the
> weight
>
> is
>
>
>
> small and I would also drop the thruster and tail
>
> assembly.
>
>
>
> Still, not much sub out of the water. With the
>
> compressor,
>
>
>
> I can open my vent valve in the hatch and use the
>
> compressor
>
>
>
> to fill the ballast tanks.
>
>
>
> > Hank
>
>
>
> >
>
>
>
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