Rebreather World - View Single Post - Fundamentals Of Constant Mass Flow (CMF) Systems

DanDunfee · 6th October 2007, 16:29

Quote: (Originally Posted by jorgey)

what i wanted to know, was, what for a IP has uncompensated 1st. stage in a CMF Rebreather, that goes f.ex. 75m like the kiss.- i mean, have they a IP near to 20bar (290psi, if i convert right) or they accept the flow decay and the diver needs to feed more often?
thanks
j o r g e

=======================

Jorge

The KISS 1st stages (Apeks DS4) are typically set for a surface IP of ~ 135 psig=9.2 bar (atm)=10.2 ata.
The IP preload springs on these regulators reportedly 'bottoms out' at a maximum of about 13.5 bar=14.5 ata. 14.5 ata / 2 (for critical sonic pressure ratio) = 6.75 atm or ~68 msw. Deeper than this, the orifice begins to go sub-sonic and the flow rate begins to drop off. This, apparently, is the main basis for Jetsams recommended MOD of 75 msw. Remember that altho they are excellent rigs, the KISSes are sold primarily for recreational and shallower technical diving..... not for deep-throat technical, caving, or wrecking.

In the Rebreather World Homebuilt Rebreather Forum, I started a Thread entitled 'Max IP for DS4 ??'. You may find it interesting. It was reported in the thread that a special spring is available (NOT from Jetsam or Apeks) to provide DS4 IPs up to ~ 20 bar. I personally have no more details on the spring or sources for it, but one of the posters claims to .

Freef (Rebreather World) has posted a lot of good modelling work on this subject, altho mostly for SCRs. Below is a URL to a good, comprehensive-but-concise, Article, courtesy of Rebreathers Worldwide- Jan Jahns & JW Beck. It contains some graphics on sub-sonic MF rolloff rates.

Gas flow through an orifice

I hope this provides the info you were seeking.

6th October 2007, 16:29	#8 (permalink)
DanDunfee Custom Title Allowed! Current Rebreather/s: Other CCR Other SCR Home Build Other Rebreather/s: Not Bought Yet Other CCR Other SCR Home Build Join Date: Sep 2005 Location: Virginia, USA Posts: 204	Re: Fundamentals Of Constant Mass Flow (CMF) Systems Quote: (Originally Posted by jorgey) what i wanted to know, was, what for a IP has uncompensated 1st. stage in a CMF Rebreather, that goes f.ex. 75m like the kiss.- i mean, have they a IP near to 20bar (290psi, if i convert right) or they accept the flow decay and the diver needs to feed more often? thanks j o r g e ======================= Jorge The KISS 1st stages (Apeks DS4) are typically set for a surface IP of ~ 135 psig=9.2 bar (atm)=10.2 ata. The IP preload springs on these regulators reportedly 'bottoms out' at a maximum of about 13.5 bar=14.5 ata. 14.5 ata / 2 (for critical sonic pressure ratio) = 6.75 atm or ~68 msw. Deeper than this, the orifice begins to go sub-sonic and the flow rate begins to drop off. This, apparently, is the main basis for Jetsams recommended MOD of 75 msw. Remember that altho they are excellent rigs, the KISSes are sold primarily for recreational and shallower technical diving..... not for deep-throat technical, caving, or wrecking. In the Rebreather World Homebuilt Rebreather Forum, I started a Thread entitled 'Max IP for DS4 ??'. You may find it interesting. It was reported in the thread that a special spring is available (NOT from Jetsam or Apeks) to provide DS4 IPs up to ~ 20 bar. I personally have no more details on the spring or sources for it, but one of the posters claims to . Freef (Rebreather World) has posted a lot of good modelling work on this subject, altho mostly for SCRs. Below is a URL to a good, comprehensive-but-concise, Article, courtesy of Rebreathers Worldwide- Jan Jahns & JW Beck. It contains some graphics on sub-sonic MF rolloff rates. Gas flow through an orifice I hope this provides the info you were seeking. __________________ There are 'Bold' divers and old divers, but NO old, ' Bold ' divers Last edited by DanDunfee : 7th October 2007 at 10:40.
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