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Hi all,
Firstly, let me apologise if I am teaching any of you to "suck eggs", but
here is what I have found out about setting up Jetstream 2nd stages.
1 Set the correct Interstage Pressure.
2 Turn on the air, and dip the 2nd stage into a bowl of water. The cracking
pressure for the servo pin should be 30mm +/-10 of water, so measure the
depth of immersion from the diaphragm centre. This is a good rough
guide to the correct sensitivity setting.
3 Alterations to the sensitivity of the servo is made by releasing the
1.5mm grub screw, and turning the knurled portion of the servo chamber
through the mouth orifice. A pair of forceps from any angling shop
will do the trick.
This moves the pin towards or away from the diaphragm. This adjustment
is extreemly sensitive, eg .001 inch on the pin, so other factors
affect the sensitivity.
3.1 Sticktion at the pin/diaphragm interface affects the consistency
of your measure of sensitivity. Dab the purge to get a consistent
reading.
3.2 A bending moment on the hose to body junction can cause a tiny
lateral movement of the pin inducing partial tripping of the servo.
I use this as a guide for the point of maximum sensitivity without
freeflow.
4 Your final setting should be such that when the sensitivity switch
is on "minus", you cannot trigger the servo by immersing the 2nd
stage, before the water level gets up to the mouth piece.
NB Obviously, when dipping the 2nd stage in water, there must be no water
in the body, as this will drastically affect your results.
-----
How you set the sensitivity is very much up to individual preference. I have
both my valves at maximum sensitivity, tripping at about 15 to 20mm water.
Because of this, I have to be careful to switch to "minus" before taking the
reg out of my mouth, and vice-versa. Even then it is important to invert the
mouthpiece at this point, and let the water enter gradually, so as not to
trigger the servo.
-----
Also beware of soaking your valve under-water after a dive. If any water gets
into the 2nd stage hose, when you next turn the air on, the water is forced
out past the servo pin, damaging it. This happened to me, and a new pin
assembly cost 30 GBP. No other damage was done. If I have any doubts about
water in the pipe, I now remove the 2nd stage and blow some air thro' the pipe.
-----
Safe Diving
Bill Dyer
Nuneaton SAC (SAA #220)
Warwickshire, UK.
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