You may have noticed that some 2nd stages have a lever on the side (like the RG-3100S) but what is it and what’s its effect?
Moving this lever switches the Venturi effect on or off, but what does that mean?
The Venturi Effect is explained as (Wikipedia):
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. The Venturi effect is named after Giovanni Battista Venturi (1746–1822), an Italian physicist.
Sounds complicated, simply put what it means is when air more through a small hole into a larger space it creates lower pressure. In the 2nd stage what this means is that it make it easier to breath (you don`t have to suck as hard), or put another way when turned off it makes it less likely for the 2nd stage to free flow
The RG-2100S is a non-adjustable 2nd stage, suitable for either a primary or secondary 2nd stage. The front cover of the 2nd stage is user changeable and available in 6 different colors (Green, Blue, Purple, Orange, Red, Yellow).
The RG-2100S comes supplied with a 75cm (29 inches)...
The RG-3100S is an adjustable 2nd stage, the pneumatically balanced design gives consistent gas flow at all times. Featuring a Venturi assist to produce a smooth inhalation, and a dive/pre dive lever to help avoid free flows on the surface.
The adjustable design allows the diver to...