J/L comparisons? Newbie question

[chrispete]

I have been regulator shopping and have noticed that the manufacturers are giving out the inhalation effort numbers in varied contexts - where one manufacturer may give theirs out as "1.4 J/L at 110 fsw" another may just say "0.9 J/L." What I am wondering is if these ratings are based on some common testing method, or do the reg manufacturers get to fiddle around and find what depth gives them the best rating?

I know that there are two main agencies that deal with this in Europe and the US, and that Europe's standards (from what I can tell) are generally more relaxed than the US's. So could the "0.9 J/L" be measured against some European standard where they test the reg's at 10 fsw and actally end up being 1.5 J/L when brought to 110?

 

[jamespitt]

hi chrispete,
i thought i could start this reply off by explaining whats behind the J/l ratio. Because of competition btw manufacturers, they quote a Work of Breathing (WOB) figure to indicate of "easy" it is to inhale and exhale from their reg.
A definition - Joule: a unit of work or energy in the meter-kilogram second system of units, equal to the work done by a force of one newton acting through a distance of one meter. (From James P. Joule, 1818-89, English physicist.)
so therefore 1 Joule is the energy used in pushing an apple (approx 1 Newton) the distance of 1 meter (in a frictionless world).
now with regs, i suppose the lower the WOB, the better breathe the reg is, kind of like being on land and having no resistance in inhaling and exhaling.
now the deeper you go, the denser air delivery gets, so the more effort is required to inhale/exhale. i guess that when taking into account WOB rates, you should be aware of at what depth the figure came about at. Rodales (www.scubadiving.com) uses the following methods:
1) Work of Breathing at 99 feet. The U.S. Navy standard test was run at this depth to establish a baseline for performance.

2) Work of Breathing at 198 feet. This is the Navy's standard test, with a supply pressure of 1,500 psi, a breathing rate of 25 breaths per minute and volume of 2.5 liters per breath. This is expressed in joules per liter with the maximum allowed 1.4 j/l.

Here are the US Navy standards for a Class A reg:
• a breathing rate of 62.5 liters per minute
• a tidal volume (lung volume) of 2.5 liters
• a depth of 198 feet of sea water
The US Navy standard for a "group A" regulator is that under these conditions the overall work of breathing does not exceed 1.4 joules/ liter.

I think the European Standard EN250 test for Regs is the same although the water temperture is about 2 deg C (for cold water), and the test may be done at 70msw rather than the 60msw the US is at. i think the Euro limit for inhale and exhale is 1.5J/l.

when comparing WOB it is important to know whether they had been tested at the same depths and all constants equal, otherwise the comparisons will be futile.

i hope i made some sense.
cheers,
James

 

[jamespitt]

havalookat this site too:
http://diver.net/capture/musac.cs.man.ac.uk/regs/select.htm

james