User's Manual

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11.2 HRU replacement
If you have an Precision 406 in an enclosure marked Category 1 then it contains a
Hydrostatic Release Unit (HRU). This has a 2 year replacement interval. The expiry
date, which is marked on the HRU and on the enclosure side label should be checked
regularly.
When the HRU expires you can obtain a replacement at a local chandler, or direct
from McMurdo at the address shown on the warranty page. McMurdo will supply an
HRU kit (Part No. 82-210B) complete with breakable plastic rod, date labels and
instruction sheet. At a chandler you should ask for a Pains Wessex “Breakthrough
HRU with an EPIRB kit”. The HRU replacement procedure is as follows:
• On the enclosure, remove the R-clip and pull the cover slowly off.
• Remove the EPIRB and stow it in a dry place.
It will activate if wet.
• Hold down the metal lever arm to take up the force of the spring.
• Push the HRU back then upwards out of the slot in the lever arm.
• When the rear clip disengages slowly release the lever arm.
• The HRU with its breakable rod can now be lifted free and replaced.
• Using pliers, remove the rear E-clip and slide off the old HRU.
• Fit the new HRU over the new rod, with its label facing outward.
• Refit the washer and the rear E-clip. Ensure rod moves freely.
• Mark the HRU with an expiry date 2 years into the future.
• Slide the HRU into the slot in the lever arm and push lever arm down.
• Engage rear washer into backplate by pushing back and sliding down.
• Look under the spring and check that the washer is fully engaged.
• Slide EPIRB into D-shaped foot on lever arm, switches outermost.
• Refit cover by engaging hole over rod and then snapping into place.
• Refit R-clip through top of rod.
• On side of cover, remove old HRU expiry date and mark new date.
1
2
Breakable rod
HRU
Lever arm
Spring
Engage
washer here
Rear E-clip
Fitting HRU
Washer