Purge in Scuba Diving


Purge is an essential action in scuba diving that involves pressing the purge button on a demand valve to induce a gas flow, which clears the demand valve’s interior of water or other substances. The purge function is a critical safety feature in modern diving equipment, designed to ensure the efficient and continuous supply of breathing gas to the diver. This encyclopedia entry delves into the purpose of the purge function, its history, and how it operates in various types of scuba diving equipment.

Historical Context

The concept of the purge mechanism dates back to the early days of scuba diving when divers primarily used open-circuit systems. These early diving systems often experienced problems with water infiltration into the mouthpiece, which could compromise the diver’s ability to breathe. To address this issue, manufacturers introduced a simple manual purge mechanism that would force a burst of air through the regulator, clearing the mouthpiece of any water or debris.

As scuba diving equipment evolved, so too did the purge mechanism. With the development of the balanced demand valve, the purge function became more efficient, responsive, and reliable, ensuring divers could maintain a steady supply of breathing gas even in challenging underwater conditions.

Purpose of Purging

Purging serves several purposes in scuba diving:

  1. Clearing the regulator: The primary function of the purge button is to clear the regulator’s interior of water or debris. This is particularly important when the diver first enters the water or when switching between regulators underwater.
  2. Preventing free flows: Purging can help prevent free flows, a situation where the demand valve becomes stuck open, causing the continuous release of breathing gas. Purging the regulator can help reset the demand valve and stop the free flow.
  3. Emergency air supply: In the event of a malfunction or low air supply, the purge button can act as an emergency breathing source, providing the diver with short bursts of air until a more stable air supply is established.
  4. Assisting buddy breathing: Purging can also be used to assist in buddy breathing situations, where one diver shares their air supply with another diver in need. Pressing the purge button on the donor’s regulator can provide a controlled flow of air to the recipient.

Types of Purge Mechanisms

There are various purge mechanisms found in different types of scuba diving equipment:

  1. Standard demand valve purge: This is the most common purge mechanism found in modern scuba diving equipment. It consists of a button located on the front of the second stage regulator. When pressed, it opens the demand valve and allows air to flow through the regulator, clearing any water or debris.
  2. Diaphragm purge: Some regulators, particularly those designed for cold water diving, feature a diaphragm purge. This type of purge utilizes the regulator’s diaphragm to initiate the purge, creating a more efficient and streamlined process.
  3. Purge on the first stage: In some diving systems, the purge function is located on the first stage of the regulator, which connects directly to the cylinder. This design allows the diver to clear water or debris from the entire regulator system.
  4. Integrated purge systems: Some full-face diving masks and surface-supplied diving systems feature integrated purge mechanisms that can clear water or debris from both the mask and the regulator simultaneously.

Using the Purge Function

To use the purge function on a standard demand valve, follow these steps:

  1. Hold the second stage of the regulator firmly in one hand, with the mouthpiece facing away from you.
  2. Place a finger on the purge button, located on the front of the second stage.
  3. Press the purge button gently and briefly. A burst of air will flow through the regulator, clearing any water or debris from the interior.
  4. If needed, repeat the process until the regulator is clear of water or debris.
  5. Before placing the mouthpiece back in your mouth, exhale forcefully to clear any residual water that may be present.
  6. Once the regulator is clear, take a cautious breath to ensure proper airflow and comfort.

Precautions and Considerations

While purging is a crucial function for divers, there are some important precautions and considerations to keep in mind:

  1. Avoid over-purging: Excessive purging can lead to a rapid depletion of your air supply. Use the purge function only when necessary, and always monitor your air consumption throughout the dive.
  2. Regulator orientation: Ensure that the regulator’s exhaust ports are facing downward when purging to prevent water from being forced back into the mouthpiece.
  3. Cold water diving: In cold water environments, the purge function can cause the regulator to freeze and malfunction. Use the purge function sparingly and consult the manufacturer’s guidelines for cold water diving.
  4. Underwater communication: Purging can create noise and bubbles that may interfere with underwater communication. Inform your dive buddy or group of your intention to purge before doing so.
  5. Practice purging: Familiarize yourself with the purge function of your diving equipment before entering the water. Practice purging on land or in a controlled environment, such as a pool, to build confidence and proficiency.

In conclusion, the purge function is an essential safety feature in scuba diving equipment that ensures the efficient and continuous supply of breathing gas to the diver. Understanding the history, purpose, and operation of the purge mechanism is critical for divers of all experience levels. By following the proper procedures and precautions when using the purge function, divers can minimize the risk of regulator-related issues and enjoy a safer, more comfortable diving experience.