VEMCO – VR4-UWM Manual
61
8.2.2
Pressurized Case
When handled correctly, the VR4-UWM pressure case and seal have a static depth rating of 500 meters (730
psi). If the receiver experiences a pressure greater than this, then water may enter the case.
If water enters the receiver case under high pressure, then some water may still be in the case when it is
returned to the surface, along with compressed air. This can be identified by its increased weight and a
sloshing sound when the case is moved.
An unexpected failure of the VR4-UWM is also an indication it might have flooded with water. If you believe
the battery should still have plenty of life left, but the VR4-UWM is unresponsive - there is no status light
activity and it will not communicate over the acoustic modem or
Bluetooth –
the main housing might have
flooded and could be pressurized. If you have offloaded a log file that indicates one or more hydrophones
have a fault, this suggests the hydrophone(s) might have flooded and become pressurized.
Another possibility is the release of chemicals from a ruptured battery, especially a lithium battery. This could
cause the case to become pressurized with hazardous fumes even if it did not leak. Or, a flooded case could
result in the rupture of the battery by corroding the cells. If you notice a strong, irritating chemical odour
coming from the VR4-UWM, this suggests the battery has ruptured and extra care must be taken.
The VR4-UWM has pressure relief valves in the main case and both hydrophones, which are designed to vent
pressure before it reaches a dangerous level. These valves require a certain amount of pressure before they
will “pop” open, so it is still possible that some pressure could be present even though the valves have not
opened. It is also possible the valves could have been blocked or fouled, preventing them from opening as
designed.
If you are suspicious there is compressed air in the receiver case, then check for air or water leaking from
seams in the case. Seams are located where the lid meets the main housing, around the perimeter of the
bottom, around the optional external connector on the bottom (if installed), around the hydrophones, and
around the three pressure relief valves.
NOTE:
Physical shocks to the receiver, such as bumping into a solid object, when it is at any
depth can result in a considerably higher pressure on the casing than just the depth pressure.
Also, if the O-rings or their mating surfaces are dirty or damaged, then water may enter the
receiver case.
All instruments that are deployed to significant depth have the
potential to become pressurized due to leakage and/or battery
failure, and when they are brought back to the surface this can
present a safety hazard. Use caution.
Wear protective clothing, gloves, and face shield when
handling a receiver that might have becomes pressurized or if
the battery might have ruptured. Keep others away at a safe
distance and place the receiver in a safe location, preferably
outdoors. Do not drop it or bump it against other objects.