Fine tuning Poseidon Jetstream second stage

[redrover31]

Hello

For those that work on their own Jetstream's, when setting up the cracking pressure do you get a repeatable reading on a magnehelic? I find I can't really sip it to the point of cracking like a downstream second, to get it set around 1.1-1.4" and have it repeatable. I did the rough set-up using the field guide and it seems to breath OK. Also tried setting it to the point of free flow, then backing it off a bit and it comes to around the same range it seems.

Any thoughts appreciated.

 

[tbone1004]

replace the servo, the seat in the servo valve may need replacing

 

[redrover31]

Thank you, will try that. Your video's were very helpful!

 

[redrover31]

Another question @tbone1004 The valve inserts in this reg are clear, rather than the blue of the current version. Are these generally OK unless there is some issue or do they degrade over time. They appear OK and reg seals up. Reg is from mid 90's I would guess.

 

[tbone1004]

Another question @tbone1004 The valve inserts in this reg are clear, rather than the blue of the current version. Are these generally OK unless there is some issue or do they degrade over time. They appear OK and reg seals up. Reg is from mid 90's I would guess.

they should be fine. If you are feeling particularly ballsy, you can disassemble the servo valve and flip the seat over which will fix it, but they are super touchy.

 

[redrover31]

Thanks, will give it a try and order up a new one either way. Can see the circlip holding it together.

 

[rsingler]

Also keep in mind that if you're doing a really precise cracking test, you can feel/hear the servo open significantly earlier (lower magnehelic reading) than the main valve. It takes enough servo opening beyond that initial trickle to decrease the pressure around the valve insert, allowing it to collapse for the rush of flow that characterizes the Jetstream. You're right - it doesn't sip like a standard second.
I call "valve opening" the second, larger airflow, which occurs at a more negative magnehelic reading. For my regs, servo trickle can start anywhere from -0.6" to -0.9". Valve opening is -1.1" to -1.4".
And I'm sure you know, but higher (more typical) intermediate pressures from your first stage will work against you. You really need the 121psi or so that is specified, to get the smoothest valve opening.

 

[redrover31]

I replaced the servo (and flipped the seat in one) and can get it cracking at around 1", all is well...until I tighten down the set screw, then the cracking increases to 1.7"+. Tried a few times, and each time I tighten the set screw it throws of the adjustment, which seems strange as the barrel doesn't move. I resorted to lightly snugging it down, which seems to leave the setting in check.

Is this common? Do you tighten the screw down, or is just a light touch required.

 

[tbone1004]

just enough for it to not spin freely. Don't crank down on it, just enough pressure to keep it from spinning. The barrel is definitely moving when you crank it down btw, but the difference in position between 1.0 and 1.7 is not a lot in these things. It is also possible your diaphragm is slightly deformed which happens when you leave it in the pre-dive position for too long.

 

[redrover31]

@tbone1004 Thanks again!