HRU (hydrostatic release unit) working & types.

                               HRU = Hydrostatic release unit

  Types :

Generally HRU are of two types
    1. Unlimited lifespan (service within 12months from date of manufacture/date of servicing and in case duration need not exceed 5 months delay)
    2. Disposable type (expiry of 2 years)

Working :

1. When ship sinks below 2 to 4m under water .the water pressure acts on HRU unit and the knife present inside the HRU unit cuts the rope passing through it and then removes the lashings of life raft.

 * There are two types of links

            1. Weak link (Red ) connected with life raft painter
            2.  Black link ( black)attached with weak link on one side and connected                                                       strongest point on deck on other side.

2. Now the lashings are removed, the life raft pulls upward and ship continues going down.  When the pulling force is 2.2+/- 0.4 KN the weak link breaks. life raft inflates.

Guys do you got any doubt comment below.
Good luck.