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Good morning, Alan,
My understanding is that the pilot and any passengers are on
board before the vacuum test. As Phil mentioned, it sets the
o-rings. This is why I was particularly interested in what pressure
differential the people are subjected to.
At 2 inches negative pressure, the "altitude" in the sub is
slightly less than 5,000 feet AGL (Above Ground Level) or ASL if
you're starting at sea level. An airliner climbs to this altitude very
rapidly (plane's pressurization system has not activated yet). You
wouldn't feel anything other than normal adjustment of your ears. HOWEVER,
when the test is over, if you suddenly opened a vent and the pressure equalized
rapidly, it would be like an instant descent from 5,000 feet to ground level
which could be painful to the ears for many people. Instead you would need
to bleed the air back into the sub slowly (minimum of a minute) to allow
people's ears to adjust. Personally I would want about a two-minute
equalization time and the ability to pause if anyone's ears were not adjusting
quickly enough.
I'm deriving all this from experience as an airplane
pilot. Phil and Dean, does all the above sound correct to you?
Corrections and comment are appreciated.
Best regards,
Jim
In a message dated 1/5/2011 1:54:36 A.M. Central Standard Time,
alanjames@xtra.co.nz writes:
Thanks Phil,
Presume there's some way of equalizing the pressure so you can
get in afterward?
I was thinking maybe leave a valve open inside the hull but closed at an
external bottle.
Have just ordered the book, "Underwater Robotics: Science, Design & Fabrication"
& noted there were some Deep Worker
photos in the preview. Did you have input into this
book other than the photos?
Regards Alan
----- Original Message -----
Sent: Wednesday, January 05, 2011 7:15
PM
Subject: Re: [PSUBS-MAILIST] Pre-dive
Vacuum
We use a small shop vac or a battery operated car vac. The
over-pressure relief valve is located externally and has smooth
barrel/cylinder casing over it - the vac hose end has a machined plastic
nozzle with an internal o ring groove and o ring. The vac is slipped onto
the pressure relief valve and a light vacuum quickly sucked - the tech
watches the cabin pressure guage through the dome and the pilot watches it
also. At a couple of pounds neg, the vac is stopped and the gauge
watched to make sure it stays steady with no leakage. The nozzle is easily
pulled off and the sub is ready to launch. Prior to pulling the vacuum, the
bellows on the O2 system is backed off so that the neg pressure doesn't
cause the O2 make-up system to function and add oxygen.
Phil
----- Original Message -----
Sent: Tuesday, January 04, 2011 8:14
PM
Subject: Re: [PSUBS-MAILIST] Pre-dive
Vacuum
Phil & Dean,
This is intriguing. What
pressure differential do you pump it to? Do you use the
over-pressure relief or another port? What's the whole
procedure?
Best regards,
Jim
Hi
Dean, have you piped the intake to the tyre inflator to use it as a
vacuum pump from the outside of the sub. Or do you sit inside &
pump air out from there. Regards Alan
From: "Recon1st@aol.com"
<Recon1st@aol.com>
To:
personal_submersibles@psubs.org
Sent: Wed, 5 January, 2011 3:46:33
AM
Subject: Re:
[PSUBS-MAILIST] Pre-dive Vacuum
Jim on my sub I installed a small air
pump I made from these small 12v
auto tire inflator. It works very
well.
Dean
In a message dated 1/2/2011 6:14:19 P.M. Central Standard Time,
JimToddPsub@aol.com writes:
Phil,
That's certainly worth putting on a pre-dive
checklist. It will definitely go on mine. How do you go
about it?
Thanks,
Jim
In a message dated 1/2/2011 1:51:25 P.M. Central Standard Time,
phil@philnuytten.com writes:
We never dive any of our subs unless they've held vacuum for
several minutes immediately prior to launch - this procedure tests
and 'sets' the o rings and avoids a nasty surprise at the end of a
large air-gap launch!
Phil |