McMaster Carr CMF orifices and filters

jmhardingjr

Hi,

I don't know if you got any information to answer this question yet, but here is what I understand about this issue.

Essentially, if you have an orifice that is constructed of metal is it usually drilled by a laser or similar means. However, due to the hardness of the material, it is not likely (at the price level that we are talking about) to be finihsed beyond this point. Thus, if you look at the hole under a microscope you will find that the edges are ragged and irregular. The surface condition of the material that he orifice is drilled in will affect the flow characteristics of the fluid (in this case O2) flowing through it. A rougher or more irregular surface contributes to turbulence which will change the flow characteristics as pressure increases or decreases. Thus, with an orifice that is drilled in metal, you will likely find much more variability in the flow. This will likely be so in a single unit as pressure changes, and also among individual units that supposedly have the same orifice size.

Also, you will find (with a relatively soft material such as brass or stainless steel) that the orifice surface will change over time and use due to erosion and corrosion of the material. The ruby or sapphire on the other hand is much much harder and resistant to wear/erosion. This will preserve the flow characteristics over time. Also, because the material is so much harder and resistant to erosion, it can be finished much more finely to produce a smoother surface that produces less turbulence. This finishing is usually accomplished by lapping the surface of the orifice with a micro wire to polish it.

All of this being said, whether or not the differences will be noticed within recreational diving parameters and with a metal orifice that is well maintained and occasionally replaced, is questionable. I would venture that for diving to 30-40 meters, you likely wouldn't see enough variability or issues to warrant worrying. Throw the snubber in the ultrasonic cleaner every 10-20 hours, recalibrate it, and then replace it annually and you are good to go. Or, buy the ruby orifice. In the grand scheme of things, they are not that expensive and even hombuilders can afford to use them if you feel the benefits are worth it. It all comes down to what you want to accomplish and how dilligently you plan to maintain your rig.

Hope this helps,

Jay

__________________


". . . the sea's in my veins, my tradition remains, I'm just glad I don't live in a trailer . . ."

Corallaro

Hi boys..

there is a description of my system for my IDA-71

1: McMastercarr Filter 10 micron
2: McMastercarr 102 microns orifice
3: MJSV-1 Shuttle 1/8 "OR" Valve
4: MJSV-1 Shuttle 1/8 "OR" Valve
5: Solded diluent manifold
6: Hose from MJV-2 O2 manual add
7: Hose from MJV-2 Diluent manual add
8: Hose from diluent manifold to wings and bailout 2d stage
9: Hose from diluent manifold to MJV-2 Diluent manual add
10:Hose from Apeks DS4 fixed 1st stage O2
NON visible: Hose from Apeks DS4 fixed 1st stage O2 to MJV-2 O2 manual add
11: Hose to counterlung (to the T piece in exhale line)
12: Apeks DS4 fixed 1st stage O2
13: Hose to O2 gauge
14: hose from IDA-71 diluent 1st stage to IDA-71 quick disconnect and to solded manifold and to ADV
15: 1,3 litres O2 bottle
16: 1,3 litres diluent bottle

the two (2) MJV-2 for manual add of O2 and diluent are on the
shoulders (like ourobouros)

Giovanni

Corallaro

and there is the front view of first arrangement of my IDA
the push button in final version are more high and better arranged

Giovanni

marekm

Hi Corallaro,

That is a nice rebreather setup you have there. Just a few questions:

1. Where did you get the DSV from, and is it a Drager?
2. Did you make or buy the PO2 meter? How well does the PO2 housing work?
3. Will you write a article about your rebreather and post it on RBW?

Cheers.
-Marek

Dave Sutton

VERY NICE!!!!

Obtains the presigious "Diver Dave Seal of Approval"

I'm going to need to do another Frankie. You guys have my stuff looking pretty crude.

Dave

__________________
"Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com

And the colors of the sea blind your eyes with trembling mermaids, For the sparkling waves are calling you to kiss their white-laced lips.
And you see a girls brown body dancing through the turquoise, And her footprints make you follow where the sky loves the sea.
And when your fingers find her, she drowns you in her body, Carving deep blue ripples in the tissues of your mind......

Corallaro

Thanks Dave!
so...now i wait the "Diver Dave Seal of Approval" stamp to glue on my unit!

Hi Marekm
1) The DSV is a Drager similar to Dolphin....an Atlantis? i buy it on a auction on eBay, it is used, new is too expensive!!! and have weights inside the hoses..
a good price for new you can found from Martin (Tauchen - Cave, Nitrox, Rebreather Ausbildung, Tec Ausrüstung, Reisen)

2) About the Po2 meter is an homemade, see this link:
http://www.rebreatherworld.com/home-...od-time-5.html

the plexiglas case is made from an craftsman of Palermo at the cost of € 130 (USD 175)

3) About write an article, it is a good idea but the unit still don't gone underwater and i am sure that need many optimizations and need many tests first, and my english is very poor....but after some underwater tests i can write it...if someone revise my english text..

saturday if the weather permit i make the first dive with a my new friend (Reb Instructor) and if i survive ....

attached the photos of the front view of current version of my unit and the photo of bailout/diluent external 5 litres bottle (the bottle in photo not yet configured) connected to quick disconnect/ switch of IDA (when connect the external bottle the internal bottle is automacally disconnected so in this mode i have a total of 6 litres of diluent bottles)

see also:
http://www.rebreatherworld.com/home-...od-time-4.html

Giovanni

PS

VERY NICE EXPLANATION ABOUT RUBY ORIFICES FROM JAY

marekm

Hi everyone,

I ran some tests today to see if different size porus disc filters have an effect on the flow rate through a 0.004" orifice.

Using air through a Scubapro MK10 with IP set to 8bar I got the following results:

With 10 micron filter upstream of the orifice the flow rate was 0.88 L/min
With 40 micron filter upstream of the orifice the flow rate was 0.86 L/min

The slight difference in result is due to errors in mearurement, as the 40 micron filter should thoeretically have a higher flow rate if anything.

So it seems you can use a variety of porus disc filters with out fear of an effect on the flow rate through the orifice.

-Marek

Corallaro

Good work Marek! thanks

the possible variables maybe the number of microholes of 10 or 40 microns in filter and if you don't use the same orifice
there are the little differences between orifices of the same type.....

the real result......IT WORKS!!

but remember the posts of Dave Sutton, Tom Rose and Jay about the maintenance of metal orifices

Giovanni

marekm

Hi Giovanni,

In another experiment I mesured the flowrate through the 40 micron filter to be 70L/min with the same 8bar drive pressure. This means that there is enough gas getting to the orifice, and the orifice is only letting out ~0.9L/min. The actual error comes from the way I did the mearurements. That is, I opened the valve and pressed start on the stop watch manually with my hands. So for the 10 micron filter the stopwatch said 1:08.4 and for the 40 micron filter 1:09.2. That roughly one second difference in timing is probably because I pressed the start button slightly later on the stop watch. The point is that the filters give so much flow rate relative to the orifice flow rate, that they are not going to have an effect on O2 CMF.

Also, thanks for your link to the PO2 monitoring setup. I just checked your warning about the PO2 being higher than actual when the low battery warning comes up. The difference I measured for air with my PO2 displays was 0.209 with full battery and 0.301 with almost empty battery. I guess that is a good reason to change batteries when the low battery warning appears.

Ok, I'm going to the post office to send you those McMaster Carr parts now that I'm finished with them.

Cheers.
-Marek

Dave Sutton

The fine color coded DSV is from FGT-1 or FGG-III.

Nice!
Dave

__________________
"Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com

And the colors of the sea blind your eyes with trembling mermaids, For the sparkling waves are calling you to kiss their white-laced lips.
And you see a girls brown body dancing through the turquoise, And her footprints make you follow where the sky loves the sea.
And when your fingers find her, she drowns you in her body, Carving deep blue ripples in the tissues of your mind......