POSEIDON SE7EN+ - Managing Ascents; Ending the Dive

Poseidon SE7EN+ User Manual Appendix 3 Page 121
Managing ascents
During an ascent from a rebreather dive, the oxygen partial pressure in the loop will begin to
drop (due to the dropping ambient pressure). The oxygen control system will likely begin to
compensate for this by injecting oxygen; however, during somewhat faster ascents, the
solenoid valve may not be able to keep up with the drop in loop PO
2
caused by the drop in
ambient pressure. This is not of great concern, unless the PO
2
gets so low that it triggers alarm
conditions; but it represents one more reason why it’s always good practice to ascend at a
slow and controlled rate.
During the ascent, loop gas will be vented from the breathing loop due to expansion. For this
reason, dives involving many ascents and descents (up and down) can lead to excessive loss
of both diluent (during descents, in re-lling the breathing loop) and oxygen (during ascents,
while trying to maintain the set-point).
Ending the dive
IMPORTANT:
Be certain that the oxygen cylinder is turned OFF prior to
completing the steps necessary for the post-dive shut-down
procedure. When the electronics shut down, the oxygen gas
supply system is vented. If the cylinder valve is open, the system
will not vent properly.
WARNING:
Always place the mouthpiece valve in the Open-Circuit position
whenever it is not in use. Doing so seals the breathing loop and
prevents water ingress into the breathing loop. Excess water in
the breathing loop can form a caustic if it comes in contact with
the absorbent material.
After surfacing and exiting the water, the Poseidon SE7EN+ electronics will continue to function
indenitely, ensuring a life-sustaining gas mixture is maintained in the breathing loop, until all
following conditions are satised:
• The depth corresponds to “0”.
• The back of the Primary Display (where the wet switch contacts are located) is dry.
• The pressure in the diluent regulator and hoses has been vented.
• The mouthpiece valve has been placed in the Open-Circuit position.
• If a M28 is connected, “Power down SE7EN” has been selected.
• Once the above conditions are met, the system will vent the oxygen gas supply system,
and power down the electronics.
• The recommended sequence of steps for the proper post-dive shut-down procedure is as
follows:
• Ensure mouthpiece is the Open-Circuit position (as it should always be when not in use).
• Turn off BOTH gas supply cylinders.
• Thoroughly dry the back face of the Primary Display, in the vicinity of the wet-switch
contacts.
• Vent the diluent gas from the system by pressing the manual purge button on the ADV.
• If SE7EN is used with a M28, select “Power down SE7EN” which is located at the end of
the root menu. Note: This menu item is only available when the other conditions for
power down are satised.
• SE7EN will now vent oxygen. If both diluent and oxygen have been successfully vented,
SE7EN powers down. When the divemode changes from “SE7EN” to “Setpoint” and the
red symbol markings for the cylinder pressures dissapears, SE7EN has completed power
down.
• Now you need to turn off your M28 Dive Computer. Choose Settings/Power/Power off.
Now the complete system is powered down.