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Diagnosing MAV & BCD Leaks During Negative-Pressure Tests

This article explains how to diagnose leaks affecting the MAV oxygen valve and the BCD diluent connector during a negative-pressure test, and provides practical steps to locate the leak safely.

Summary

  • Key safety and diagnostic steps for negative-pressure testing of the loop and BCD/diluent connections.
  • How valve direction and spring behavior can cause apparent leaks during a negative-pressure test.
  • A simple method to locate the leak using pressurization and submersion.

Important principle

  • The MAV valve seals in only one direction. Under negative pressure the valve spring is lightened; if there is pressure from the opposite direction it can push the valve open and allow air to pass into the loop, causing the loop pressure to rise during a negative-pressure test.

Preparation before a negative-pressure test

  1. Close the diluent valve. The diluent valve must be closed while performing a negative-pressure test.
  2. Make sure there is no pressure in the diluent regulator or the diluent hoses. The hoses and regulator should be depressurized before you start.

Performing the negative-pressure test

  1. With the diluent valve closed and hoses/regulator depressurized, create the negative pressure in the loop per your normal testing procedure.
  2. Listen and observe for any flow or leakage. If you hear leakage at the BCD connector or observe negative flow from the ADV toward the BCD connector, note that location.

Locating the leak using pressurization and submersion

  1. Pressurize the system (for leak localization), then fully submerge the unit in water.
  2. Watch for bubbles to identify the exact location of leakage. Submersion while pressurized will show visible bubbles at the leak point.

If a leak appears during a negative-pressure test

  • Confirm you followed preparation steps (diluent valve closed; no pressure in diluent regulator/hoses).
  • If leak is heard at the BCD connector and negative flow is observed from the ADV toward the BCD connector, suspect flow caused by valve directional behavior (spring/lightening under negative pressure allowing opposite-direction flow when pressure exists on the other side).

When to contact support

  • If you cannot identify or stop the leak after closing the diluent valve, depressurizing hoses, and locating the leak by submersion, prepare diagnostic information (including unit serial number) and contact technical support for further assistance.

Conclusion

  • Always close the diluent valve and ensure no pressure in the diluent regulator or hoses before performing negative-pressure tests.
  • The MAV valve’s one-direction sealing and spring behavior can let air through when opposing pressure exists; this can cause apparent leaks during negative-pressure testing.
  • Pressurize and submerge the unit to visually locate leaks by observing bubbles, and provide the unit serial number to support when requesting further help.