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Ambient Pressure Diving's ADV The new Ambient Pressure Diving's auto diluent valve, which was released in February 2003. Inspiration diving practice to date (i.e. without an ADV fitted) requires the manual addition of diluent by the diver on descent to maintain loop volume as the counterlungs become compressed. This is achieved via the dil-add button on the inhale counterlung. The ADV makes this task uneccessary as it is pressure activated and therefore will automatically add diluent on descent. The ADV is fitted in place of the inhale T-piece on the left shoulder counterlung - usually with the diaphragm facing the diver's head. It is activated by a pressure differential across the diaphragm and it supplies gas to the loop (breathing circuit) whenever a substantial negative pressure is experienced within the inhale counterlung. |
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| Design & Connections The gas supply hose connects with a 3/8" UNF thread to the low pressure port on a first stage or into the diluent port on the Inspiration's manifold. It connects to the ADV via a 300º swivel connector. This swivel allows the hose to be fed from the rear e.g. from the manifold or from the front e.g. from a side-mounted diluent cylinder. NOTE: If you need the facility to remove this side-mounted cylinder in-water an APD Quick-release Connector will shortly be available as an optional extra. (expected early summer 2003). The ADV is an upstream valve and can be used with 1st stages delivering 7 to 11 bar (nominal 9.5 bar) above ambient and requires no adjustment. The elastomeric diaphragm cover also allows manual operation of the ADV. |
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| Using The ADV During descents it is normal for the ADV to add gas on nearly every inhalation. However, this is most abnormal during all other phases of the dive. Normally the ADV adds gas to make the counterlung breathable and then stops. WARNING!! If the ADV operates on every inhalation this is an indication of either poor rebreather diving practice, such as exhaling unnecessarily through the nose, or is a sign of some other leak from the loop. Any extra diluent addition usually has the effect of reducing the PO2 within the breathing circuit and would be countered by the oxygen controller adding oxygen to regain the setpoint. The danger of inadvertently using excess gas from both diluent and oxygen cylinders is higher when using an ADV and extra monitoring of cylinder contents gauges should take place. Located on the left shoulder, rolling left side down may force the ADV to add gas to the loop as will rotating head down, when the gas in the counterlungs migrates upwards away from the ADV and causes a negative pressure on the inside of the diaphragm. Whenever these manoeuvres are undertaken you may need to run the counterlungs with a higher gas volume than normal. |
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