Alan, one more thing: Even a small, onboard air pump is
going to be LOUD in a small enclosed space. We'll have come up with
various methods to mitigate that. I know I'll use a headset for ear
protection while the pump is running, might not use one for COM; I want to hear
everything going on around me.
Oops... phone call interruption and I see a couple of emails
came in.
Dean, tell me if I'm understanding you correctly. With
an internal compressor you can close the hatch and draw
air from the interior into a tank to create the vacuum instead of pumping
air overboard. Are you using a small dedicated tank or another onboard
tank? You also have it plumbed to draw outside air. I'm not sure I
understood all you were saying.
Regards,
Jim
In a message dated 1/5/2011 10:09:03 A.M. Central Standard Time,
JimToddPsub@aol.com writes:
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 |