NEEDLE VALVES

[jale]

Hi
Here is an example of a old home-made needle valve I used.
These were quite popular in cave diving in Europe.

 

[rjack321]

Why is your orifice not standard? Was that a Kiss error or did you make a change?

Either Kiss error or manufacturing defect. To get 0.7 LPM flow on that MAV I have to dial the IP back to about 115psi. I only use that MAV in sumps and in Mexico so it's fine.

 

[Heat Miser]

pro: you can dive with a dynamic 1st and not have to continually dick with the knob. you really only need to touch it for workload changes. So no depth limit

Is there a paper or website that can demonstrate the two CMF flow chart, I'm having problems conceptualising.

I hear you that the advantage, is to be able to use a normal reg rather than an absolute pressure reg. I just don't understand the physics.

Is it because the needle valve on the two CMF's can be gradually opened at depth?

 

[Heat Miser]

one isn't enough to really stabilize the flow rates so you still have to mess with it with depth changes. The second one stabilizes it to where the IP shift from surface to depth is not really relevant.

Don't worry did a google search, found the July answer to same question

 

[dupsteve]

In theory you can use a dynamic 1st stage in any needle valve. In practice you will be f***ing with that tiny tiny knob constantly with even minor changes in depth (up down 20ft). It's a colossal pita with dry gloves on, or using a scooter, or with a camera.

Going from 0.2 LPM up to 1.2 LPM (who works harder than that diving?) is about 3/4 to 7/8ths of a turn. It's way easier to use a blocked 1st with a stronger spring so you can run a 200psi IP. That's a 400ft dive before you need to worry about your O2 shutting off.

Including a CMF in a needle valve negates one of the best features, the plain needle valves are clog proof.

what you mean by CMF in needle valve VS plain needle valve?? I dive meg (manual copis) and i am planing to go bmcl...needle valve would be a new piece of equipment for me, that's why i am asking...
tks

 

[grantctobin]

what you mean by CMF in needle valve VS plain needle valve?? I dive meg (manual copis) and i am planing to go bmcl...needle valve would be a new piece of equipment for me, that's why i am asking...
tks

There are a few needle valves in existence that have orfices inside of them, thereby decreasing the amount of fussing needed with the valve when using an unblocked first stage.

The easier answer is just using a blocked first stage with a needle valve from Fathom/SubGravity/Chris Kennedy.

 

[dupsteve]

There are a few needle valves in existence that have orfices inside of them, thereby decreasing the amount of fussing needed with the valve when using an unblocked first stage.

The easier answer is just using a blocked first stage with a needle valve from Fathom/SubGravity/Chris Kennedy.

Tks did you tried it in cold water using big drygloves? Knob look very tiny and it's between the 2 hoses ....

 

[grantctobin]

Tks did you tried it in cold water using big drygloves? Knob look very tiny and it's between the 2 hoses ....

I have. It is hard to tell how much you’ve rotated it, but squeezing to twist it is doable. Some people put a zip tie on the knob itself to give more tactile feedback.

 

[rddvet]

Tks did you tried it in cold water using big drygloves? Knob look very tiny and it's between the 2 hoses ....

THe fathom has become popular enough that it's being used by non-cave divers. There are quite a few people who dive cold water with gloves and I've never heard any major complaints

 

[flymolo]

Tks did you tried it in cold water using big drygloves? Knob look very tiny and it's between the 2 hoses ....

Yes, works totally fine with dry gloves.