Calculating volume of a loop

cedricverdier · 20th July 2005, 07:09

Hi,

For a Rebreather homebuild project, I need to calculate the total volume of a loop.

So is there anyone with a clever (and practical) idea?

BTW filling the loop with water is not an option because of some un-removable electronics

Cheers

***Beanie*** · 20th July 2005, 07:49

fill with air and drop into water measure the displaced volume of water

would that work for you

decoweenie · 20th July 2005, 10:03

Quote: (Originally Posted by Beanie)

fill with air and drop into water measure the displaced volume of water.

I don't believe that would give the loop breathing volume since it would only give the (as you mentioned) displacement volume of the unit.

IMHO, I would approach it this way:

Establish the mininum loop volume on your homebuild
Use your lung to "transfer" this volume into an empty bag that you could seal
Dunk the sealed plastic bag in the water to find its displacement volume. Or use a bag with a known volume for reference.

***schford*** · 20th July 2005, 10:09

I don't think that would work Phi unless you could compress every part of the loop - I don't think you could completly empty the breathing hoses for example.

No ideas myself though

Drmike · 20th July 2005, 10:25

Approximate each part of the loop to a geometric shape, cylinder for hoses, cuboid for lungs etc, calculate each shapes volume and add it all up?

decoweenie · 20th July 2005, 10:27

Quote: (Originally Posted by schford)

I don't think that would work Phi unless you could compress every part of the loop - I don't think you could completly empty the breathing hoses for example.

No ideas myself though

Do you think there would be more gas left inside the loop when you pull a negative pressure (i.e. negative loop test) ?

Drmike · 20th July 2005, 10:36

Quote: (Originally Posted by decoweenie)

I don't believe that would give the loop breathing volume since it would only give the (as you mentioned) displacement volume of the unit.

IMHO, I would approach it this way:

Establish the mininum loop volume on your homebuild
Use your lung to "transfer" this volume into an empty bag that you could seal
Dunk the sealed plastic bag in the water to find its displacement volume. Or use a bag with a known volume for reference.

That should do it.
You could use a balloon.

decoweenie · 20th July 2005, 10:40

Quote: (Originally Posted by Drmike)

You could use a balloon.

Just a thought...

Anything elastic will probably "compresses" the gas a little bit so there will be a minute error, but not enough to worry about.

How about a large drinking sport bag that could be sealed fast and easy ?

Andy M · 20th July 2005, 10:44

Quote: (Originally Posted by cedricverdier)

For a Rebreather homebuild project, I need to calculate the total volume of a loop.
BTW filling the loop with water is not an option because of some un-removable electronics

I believe the only way for you to get an accurate measurement is to use a liquid to fill the loop. If accuracy is important, you will need to remove the electronics.

Why cant you remove them anyway? You should be able to for ease of maintenance... design fault?

Andy

***schford*** · 20th July 2005, 10:52

Quote: (Originally Posted by decoweenie)

Do you think there would be more gas left inside the loop when you pull a negative pressure (i.e. negative loop test) ?

I think there is a substantial portion of gas left in the loop when I do a negative test. The only way for there to be no gas and to get an accurate measurment of the loop volume would be for me to create a vacuam which is not going to happen with my lung power!

Stuart

20th July 2005, 07:09	#1 (permalink)
cedricverdier S21 M.I.B. Current Rebreather/s: Evolution Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Sport Kiss Classic Kiss Join Date: Apr 2005 Location: Worldwide! Posts: 494	Calculating volume of a loop Hi, For a Rebreather homebuild project, I need to calculate the total volume of a loop. So is there anyone with a clever (and practical) idea? BTW filling the loop with water is not an option because of some un-removable electronics Cheers __________________ Cedric Verdier PADI Course Director, ANDI-IANTD-PSAI-TDI-DSAT-DAN-NAUI-CMAS Instructor Trainer Trimix (CCR and OC) and Cave Diving Instructor Trainer www.CedricVerdier.com DIRrebreather member
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20th July 2005, 07:49	#2 (permalink)
*Beanie* Close to that red button Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,207	fill with air and drop into water measure the displaced volume of water would that work for you __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk www.divelife.co.uk
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20th July 2005, 10:03	#3 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,510	Quote: (Originally Posted by Beanie) fill with air and drop into water measure the displaced volume of water. I don't believe that would give the loop breathing volume since it would only give the (as you mentioned) displacement volume of the unit. IMHO, I would approach it this way: Establish the mininum loop volume on your homebuild Use your lung to "transfer" this volume into an empty bag that you could seal Dunk the sealed plastic bag in the water to find its displacement volume. Or use a bag with a known volume for reference.
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20th July 2005, 10:09	#4 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,674	I don't think that would work Phi unless you could compress every part of the loop - I don't think you could completly empty the breathing hoses for example. No ideas myself though
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20th July 2005, 10:25	#5 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Approximate each part of the loop to a geometric shape, cylinder for hoses, cuboid for lungs etc, calculate each shapes volume and add it all up? __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment
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20th July 2005, 10:27	#6 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,510	Quote: (Originally Posted by schford) I don't think that would work Phi unless you could compress every part of the loop - I don't think you could completly empty the breathing hoses for example. No ideas myself though Do you think there would be more gas left inside the loop when you pull a negative pressure (i.e. negative loop test) ?
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20th July 2005, 10:36	#7 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Quote: (Originally Posted by decoweenie) I don't believe that would give the loop breathing volume since it would only give the (as you mentioned) displacement volume of the unit. IMHO, I would approach it this way: Establish the mininum loop volume on your homebuild Use your lung to "transfer" this volume into an empty bag that you could seal Dunk the sealed plastic bag in the water to find its displacement volume. Or use a bag with a known volume for reference. That should do it. You could use a balloon. __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment
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20th July 2005, 10:40	#8 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,510	Quote: (Originally Posted by Drmike) You could use a balloon. Just a thought... Anything elastic will probably "compresses" the gas a little bit so there will be a minute error, but not enough to worry about. How about a large drinking sport bag that could be sealed fast and easy ?
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20th July 2005, 10:44	#9 (permalink)
Andy M Dude Current Rebreather/s: Home Build Other Rebreather/s: Sport Kiss Home Build Join Date: Mar 2005 Location: Cambridge, UK Posts: 415	Quote: (Originally Posted by cedricverdier) For a Rebreather homebuild project, I need to calculate the total volume of a loop. BTW filling the loop with water is not an option because of some un-removable electronics I believe the only way for you to get an accurate measurement is to use a liquid to fill the loop. If accuracy is important, you will need to remove the electronics. Why cant you remove them anyway? You should be able to for ease of maintenance... design fault? Andy __________________ Know your PO2 at all times
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20th July 2005, 10:52	#10 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,674	Quote: (Originally Posted by decoweenie) Do you think there would be more gas left inside the loop when you pull a negative pressure (i.e. negative loop test) ? I think there is a substantial portion of gas left in the loop when I do a negative test. The only way for there to be no gas and to get an accurate measurment of the loop volume would be for me to create a vacuam which is not going to happen with my lung power! Stuart
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