Poseidon SE7EN User Manual
Appendix 3 Page 98
Before reaching this test (indeed, before Powering-up the electronics), it’s important to make
sure that the over-pressure relief valve on the bottom of the right (exhale) counterlung is
adjusted to the full clockwise position. As mentioned previously, the mouthpiece should be in
the OC position, and the oxygen cylinder should be turned on. Also, the counterlungs should
be no more than half inflated and the over pressure valve (OPV) should be fully closed (turned
clock wise).
IMPORTANT:
Make sure the over-pressure relief valve on the bottom of the right
(exhale) counterlung is adjusted to the maximum cracking pressure
(turned all the way in the clockwise direction). Also ensure that
the mouthpiece is in the OC position, that the oxygen cylinder
valve is turned on, and the counterlungs are not already inflated.
Otherwise, Test 49 will fail. Make sure that nothing pushes against
the OPV, that will cause the Test 49 to fail.
Figure 2-9.
Test 49 - Positive pressure loop test.
The sequence of events for Test 49, and the various corresponding tests that are conducted,
are as follows. First, the system injects oxygen into the breathing loop until the counterlungs
are both full, but not tight (detected by the depth sensor as a slight pressure increase). This is
why it’s important that the counterlungs not already be fully inflated prior to starting Test 49
(which can occur if the cylinders are turned on and the mouthpiece is in the OC position during
tests 24–27). This initial inflation is done via one of the two metabolic oxygen solenoid valves,
thereby ensuring that this solenoid valve is actually injecting gas when it is supposed to.
Once the counterlungs are fully inflated and the depth sensor detects a slight increase in
pressure, the system pauses and monitors internal loop pressure for 20 seconds. If any of the
four solenoid valves are leaking, the pressure inside the breathing loop will gradually rise.
Assuming no increase in loop pressure is detected during this 20-second period, the second
metabolic solenoid valve is used to inflate the breathing loop to a higher internal pressure.
When this happens, the counterlungs will be tightly inflated, and the internal pressure should
be slightly less than the cracking pressure of the over-pressure relief valve on the bottom of the
right counterlung, when that valve is adjusted to its maximum cracking pressure. The system
then monitors the loop pressure for the next 20 seconds to determine whether the pressure
decreases, as by a leak in the breathing loop.
Battery power verification (Test 48)
Immediately after passing the two gas pressure tests, the pre-dive routine tests whether there
is sufficient battery power to begin a dive (Test 48). The amount of power required depends on
how recently the battery was subjected to a Learn Cycle during charging (see Chapter 1). If
the Learn Cycle occurred recently, then the system is able to predict the remaining battery life
relatively accurately, and Test 48 will pass if the battery has at least 20% charge remaining
(approximately 5–6 hours of typical dive time, or 4 hours of night-diving time). The amount of
charge required to pass this test increases by 0.5% per day since the last Learn Cycle, such
that after 160 days with no Learn Cycle, Test 48 will not pass.
This test will pass or fail immediately. If it fails, the only remedies are to re-charge the battery
(and/or subject it to a Learn Cycle), or replace the battery with another one with greater charge
(subject to decompression data discrepancies, as discussed previously for Test 40).
Positive pressure loop test (Test 49)
One of the most basic pre-dive tests for any rebreather is to make sure that the breathing loop
is intact and not leaking. Water entry into the breathing loop can cause serious problems if
mixed with the CO
2
absorbent material in the cartridge. As discussed earlier in this Appendix,
a manual negative pressure loop test can help detect leaks in the breathing loop.
Another common test is the Positive Pressure Loop Test (PPLT), which is similar to the Negative
Pressure Loop Test, except the test is performed by pressurizing the breathing loop with
positive pressure. Like the Negative Pressure Loop test, this test could very easily be performed
manually. However, one of the features of the Poseidon SE7EN – the placement of the depth
sensor within the breathing loop – allows this test to be performed automatically (Figure 2-9).
Test 49 actually performs four separate tests, only one of which is the PPLT. The other three
are:
• Verifies depth sensor is sensitive to small pressure changes
• Verifies that both metabolic oxygen solenoid valves are injecting gas
• Tests for leaks in all four solenoid valves.
