Dive mode or +/- on regulator second stage

[krukster86]

When I was using rental ScubaPro regulators, I noticed that there was a dial on the side of the second stage. I believe the range was labeled + / -, dive mode or something similar. I asked the divemaster about it before we departed and he said that this dial affected the flow of air to the regulator second stage. One setting is for breathing on the surface and the other is for breathing while submerged, something about one setting minimizes excess flow while submerged.

Anyone have a detailed explanation? Thanks in advance

 

[Randy43068]

My answer. It depends. When I'm diving deep I sometimes move the lever to the + side a little or if I'm shallow and doing something that requires some heavy breathing. Otherwise I have the lever in -0- or maybe even - position. Truth be told, I could live without the lever.

 

[buddhasummer]

The minus is usually used to prevent free flows on the surface. I turn mine to positive once head goes under on primary, backup stays on minus never had a free flow.

 

[supergaijin]

a) Sounds like a venturi lever. When in + position, it directs air directly to the mouthpiece, thus decreasing 'work of breathing'. When set to - the air is deflected upwards reducing the flow.

b) Some regulator models have a 'Dive' position which affects a lever inside the second stage so that it breathes normally. When set otherwise, the reg can still be breathed from, but with difficulty. The idea I believe is to prevent unwanted free-flows from very sensitively tuned second stages.

.

 

[chrpai]

You can find the manual for the regulators here:

http://www.scubapro.com/media/59907/scubapro_regulators-english.pdf

Section 7.1 covers your question.

 

[krukster86]

You can find the manual for the regulators here:

http://www.scubapro.com/media/59907/scubapro_regulators-english.pdf

Section 7.1 covers your question.

Perfect. Thanks!

 

[DivemasterDennis]

My Legend had the same feature, and I offer a word of caution: if you are too far to the + side on a dive, you will find there is a "bleed over" effect when breathing, with some escape of air from the reg. As in adding/subtracting air from a bc, use miniscule increments to tune the reg to you personal preference or setting. The - setting is convenient to minimize free flow at the surface, but you won't want to leave it there. I have found that a slight + setting in cold water is comfortable for me. It is all a matter of person preference. My other regs do not have the feature.
DivemasterDennis

 

[windapp]

Second stages can have two types of adjustment.

The first type adjusts the spring compression and is probably the +/- adjustment you saw. This adjusts the amount of vacuum required to open the valve. The main reason for making this diver adjustable is so that you can turn it down a little if you are diving into a current, and the current is pushing on the diaphram. I know people who like to turn it down a little to help control their breathing rate.

The second is a venturi assist. In one position, it directs the flow of air against the diaphram to reduce the vacuum so that the valve tends not to free flow if it cracks a little (pre-dive position). The second directs the air so that it actually increases the amount of vacuum you are pulling on the diaphram when you are inhaling (dive mode). This is different from the spring adjustment because it only changes the effort while you are inhaling after the valve has already cracked, and therefore does not change the cracking pressure.

 

[krukster86]

This would explain why the regulator went into free flow mode when I practiced losing the regulator underwater. I had it set to Dive Mode or 100% "+".

 

[windapp]

This would explain why the regulator went into free flow mode when I practiced losing the regulator underwater. I had it set to Dive Mode or 100% "+".

A well adjusted regulator should free flow under the water out of your mouth if the mouthpiece is facing up. This is because the cracking vacuum should be about 1 inch of water, and the distance between the diaphram and the mouthpiece outlet is usually more than 1 inch.