Venturi Adjustment on Scuba Regulators (Dive/Pre-Dive, Off-On, and +/- Switch)

By Natalie Gibb, About.com Guide

What do you notice about the design of a regulator second stage? At first glance a diver may notice the size, weight, or color. Perhaps you notice an interesting little knob on the second stage labeled "Dive/Pre-Dive," "On/Off," or "+/-". This switch or knob alters the airflow inside the regulator, making breathing either easier or more difficult. Turning the knob enables and disables something called the Venturi Effect, which regulator designers take advantage of to assist breathing. Click through the following pages to find out how it works, and when you should disable the Venturi Effect.

Previous

• The Pre-Dive/Dive, On/Off, or +/- Adjustment on a Scuba Regulator
• What Is the Venturi Effect?
• Regulator Second Stage Function (Really) Simplified
• Venturi-Assited Breathing
• The Downside of the Venturi Effect - Easy Free flow When Enabled
• How to Avoid Free Flow Caused by the Venturi Effect
• The Take-Home Message About Venturi Adjustments on Regulators

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