[PSUBS-MAILIST] flow meters

Tue Mar 13 22:55:52 EDT 2018

How an engineer controls the Oxygen level in a Psub

Take HP O2 (2200 psig max) stored in external tank/tanks and bring this
thru the hull using ¼” tubing and have a hull isolation valve on the inside
of the hull.  Bring the HP O2 into a box using Swagelok fittings.  In the
box , use a pressure reducing regulator to drop the pressure to 5-10  psig.
Feed this reduced pressure O2 into a  0-10 SLPM O2 combination mass
controller /meter that you source from ebay.  Control the O2mass rate  into
the boat by sending a 0-5 VDC control signal from either a potentiometer
off a 5VDC regulated power supply or a PLC analog voltage output card.   Put
a Swagelok Vernier needle valve (SS-SS4-VH) in a bypass around the O2 mass
controller for manual control in the event you loose power.  Put a 0-3000
psig O2 pressure sensor to measure the pressure of the HP O2 on the tubing
as it enters the box.  Read the mass rate output signal (0-5VDC) of the O2
in SLPM from the combination mass controller /meter.  Display this on a
analog gage or PLC HMI.  Put the mass controller input signal under the
control of a PID loop with the set point being 20.95 mole percent O2.  Measure
the mole percent of O2 in the cabin as the process variable.  Use an
inexpensive plastic variable area meter (0-5 SLPM) on the LP O2 discharge
as a backup sensor in case you loose power.  This system will hold the O2
mole percent constant in the boat regardless of the size of the pilot or
his/her O2 consumption rate and regardless of the cabin pressure and
temperature in the boat.  Lock out the PID loop if the hatch switch is open.
Set up alarms for high and low O2 levels as per ABS.  Set up alarm for low
O2 tank pressure.  In the same box install cabin pressure and temperature
sensors, a relative humidity sensor, as well as O2 and CO2 mole percent
sensors.  After installing this box in your boat, do extensive shop dives by
getting someone to volunteer to be the guinea pig with the hatch closed and
data log the sensors from the box over a extend period of time say 10 hours.
Tune the PID controller as needed until O2 level remains relatively
constant.

To improve system, add redundant sensors and add PLC ladder logic to detect
bad sensors.  Can also improve system by measuring the O2 mole percent in
the inlet O2 gas stream to make sure it pure O2 and not Argon or some other
gas.

How non engineer controls the Oxygen level in a Psub
When you feel light headed, surface, blow MBT and open hatch.  After head
clears, close hatch and resume dive.

Cliff

On Tue, Mar 13, 2018 at 8:08 PM, Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Alan,
>              I would eventually like to do that bellows add system but I'm
> not sure where I would get the tilt valve part of the system.  Could that
> be had from scuba mouth piece parts ?
>
> Brian
>
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] flow meters
> Date: Wed, 14 Mar 2018 12:57:14 +1300
>
> Brian,
> I can't see what it's maximum inlet pressure is, but on another site it is
> saying they are calibrated for an inlet pressure of 50psi. So would need
> a regulator set to output 50psi & be rated for the inlet pressure you want.
> I think those paediatric regulators have a 50psi output pressure so it
> should work putting it in line with your flow meter but it is a bit of a
> strange
> set up. I would have just gone with a normal regulator. See if you can
> find out more info on your flow regulator model.
> If you have a needle valve before your regulators to bypass them you can
> just turn that on & off if all else failed.
> Alan
>
>
> Sent from my iPad
>
> On 14/03/2018, at 11:43 AM, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Alan,
>              My plan was to go from my med regulator to my flow meter, My
> flow meter ( recommended from Cliff)  has a range between 0 and 5 lpm.  But
> I'm not really sure what the supply pressure for my flow meter is suppose
> to be.  My O2 bottle is still sitting down at the dive shop , so as soon as
> I get it I'm going to test things out.
>
> Brian
>
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] flow meters
> Date: Wed, 14 Mar 2018 11:24:00 +1300
>
> Brian, Rick,
> GL is saying O2 consumption is 15 l/h resting, 40 l/h working & 26 l/h
> average.
> (.43 litres per minute. ) Even my paediatric click regulator isn't fine
> enough by the
> look of it, it does 1/4 of a litre, (.25) then the next step is 1/2 (.5)
>  You have got me rethinking this Rick. I might go with a flow meter so I
> can
> finely adjust it & stop a potentially noisy O2 add system turning on & off
> frequently.
> Brian your 0-8 litre regulator seems to have the same increments in the low
> range as my 0-4 litre regulator so you aren't loosing anything with it.
> Alan
>
> Sent from my iPad
>
> On 14/03/2018, at 10:07 AM, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> My medical O2 regulator goes from 0 to 8 lpm  ,  My scuba shop finally got
> my bottle filled !  They had lost a transitional fitting needed to fill the
> bottle so I've been waiting for about two weeks now.  It's a good thing
> they got the part because there is literally no other place around who will
> fill it !    Don't ask me how or why they are so easy about filling the O2
> but I checked every other dive shop within 100 miles and nobody would do
> it.  Believe me I'm not asking any questions, just thanking them for my
> fill  ;-)
>
> Brian
>
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Rick Patton via Personal_Submersibles <personal_submersibles at psubs.
> org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] flow meters
> Date: Tue, 13 Mar 2018 10:39:44 -1000
>
> Alan,
>
> So you have the second one you listed so you are bringing the HP 02 right
> up to that?
>
> Rick
>
>
>
> On Tue, Mar 13, 2018 at 10:08 AM, Alan via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Rick,
> just looked at my 0-4 LPM paedeatric click style oxygen meter & it says
> "maximum pressure not to exceed 2600 psi."
> Alan
>
> Sent from my iPad
>
> On 14/03/2018, at 8:13 AM, Alan via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Rick,
> as you say "above ambient" so at 350' depth you will have 130psi
> coming out of the regulator plus another 175psi for the ambient depth.
> EMT have this...https://www.emtmedicalco.com/GENTEC-OXYGEN-FLOWMETER-WITH-
> REGULATOR-0-15-LPM-CGA-870-OR-540-191M.htm
> I bought a pressure regulator for inside the hull to deal with that,
> however the click style paediatric regulators they have take a high inlet
> pressure
> although I can't see any literature on this at EMT.....
> https://www.emtmedicalco.com/PEDIATRIC-REGULATORS-0-4-LPM-CGA-870-8704.htm
> Alan
>
>
> Sent from my iPad
>
> On 14/03/2018, at 6:53 AM, Rick Patton via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Was looking into buying an 02 flow meter yesterday online and was told
> that the incoming pressure to the meter had a max incoming working pressure
> of 50 psi. My bottles will be on the outside and I have two 02 cleaned
> first stage regulators that will take them from HP to LP then into the sub.
>  I guess the average LP setting is  around 150 psi + -above ambient? so I
> should be able to have a dive shop re set them down to 50 psi? What have
> others done that have the same scenario and wonder if there are flow meters
> that can take the 150 psi in?
>
> Rick
>
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