|
Alan,
I plan to set up the vac system onboard to be controlled
completely by the pilot. I might not have the same support team all the
time and therefore lack a person on the outside who is experienced in the
operation of the pre-dive vac test. In a more sophisticated or commercial
operation this would not be the case. With me being the pilot I would have
been through the procedure several times in garage dives before ever getting it
wet as well as repeating it on every subsequent wet dive per the
checklist. That way I would be the most experienced in how it feels and
the times of each segment of the test sequence.
Even after all the test dives are complete and I've moved into
the regime of "routine" operations, I'll always have some support team on every
dive including at least one person who tends toward the anal on matters of
safety. Hopefully having a two-person vessel will make it easier to
recruit support personnel with the promise of a dive.
As a side note, I'll want to provide for shade over the
bubble canopies while the sun is beaming down. It can get extremely hot in
there with the canopies closed until you can get underwater.
Cheers,
Jim
In a message dated 1/5/2011 9:12:26 A.M. Central Standard Time,
alanjames@xtra.co.nz writes:
Thanks Jim,
Yes that makes sense. & using a small car vacuum may be a
safety factor
in that it might not develop enough negative pressure to harm
anyone.
I don't see myself having a support team on a lot of occasions & was
thinking
along the lines of one person doing the test.
Alan
----- Original Message -----
Sent: Thursday, January 06, 2011 2:26
AM
Subject: Re: [PSUBS-MAILIST] Pre-dive
Vacuum
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 |