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Operation of a Hydrostatic Release Unit

Overview
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A hydrostatic release unit or HRU is a pressure activated mechanism designed to automatically deploy when certain conditions are met. In the marine environment this occurs when submerged to a maximum depth of four meters. The pressure of the water against a diaphragm within the sealed casing causes a plastic pin to be cut thereby releasing the containment bracket casing, allowing the EPIRB to float free.

EPIRB hydrostatic release mechanism

Description

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A hydrostatic release unit is a type of pressure activated release mechanism(ARM). Some common characteristics of HRUs are:

  • Water pressure sensitive at depths not to exceed four meters or less than two meters
  • Single use only, require replacement if activated
  • Cannot be serviced; only replaced
  • Waterproof; sealed against moisture and tampering
  • Must be labeled with expiration date
  • Expiration date is two years from month of installation applies to unit and rod


Regulations and Technical Specifications Governing EPIRB, Hydrostatic Release Devices

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  1. Corrosion Resistance Test
  2. Temperature Tests
  3. Submergence and Manual Release Test
  4. Strength Tests
  5. Technical Tests on the Membrane
  6. Performance Test

Operation Video

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Although this demonstrates a HRU for a life raft, the EPIRB HRU works on the same principle.

Operation of a Hydrostatic Release Unit

References

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Notes
  1. ^ Life-saving appliances: including LSA code/ International Maritime Organization (2nd ed.). London. 2010. ISBN 9789280115079. {{cite book}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)CS1 maint: location missing publisher (link)

Category:Maritime communication