closed-circuit rebreathers...

Principles of Operation

The PRISM Topaz is a digitally controlled, constant PO2, modular, closed circuit diving system.

It's breathing loop consists of a closable mouthpiece assembly with mushroom/check valves either side, which ensure uni-directional flow. Dual, front mounted counterlungs provide the diver with a flexible reservoir equivalent to the maximum displacement of the diver's own lung volume. These counterlungs are fitted with both automatic and manual gas addition systems and a variable volume control valve (used upon ascent to vent excess expanding gas volume or to purge the loop). A radial flow scrubber canister is mounted vertically on a backplate attached to the integrated BC, between twin supply cylinders (one each, oxygen and diluent). An optional cowling may be fitted.

The electronics, sensors and batteries are mounted in the electronics head assembly at the top of the scrubber, with supply hoses feeding over the diver's shoulders into the top of the counterlungs. A lighted primary display offers a quick reference of unit performance with status and alarm indicators. An independent secondary display driven totally by the sensors themselves and requiring no battery, verifies the unit's performance. With the electronics switched on the secondary also provides a status check for the battery and displays the set point selected for the dive. The electronics vote between the three proprietary galvanic sensors and control the operation of a low wattage solenoid valve on the oxygen supply. Diluent addition is automatically achieved as hydrostatic pressure increases and the counter lung collapses against the valve actuator. Fully charged, in standard configuration, the unit weighs approx. 47lbs and has a recommended scrubber duration of five hours.

A typical inhalation cycle (see diagram at right, secondary not shown) has the diver inhaling from the right (inhalation) lung, through the mouthpiece assembly into the left (exhalation) lung. The exhaled gas will then pass up over the diver's left shoulder and into the radial scrubber canister where it will travel down the inner tube and diffuse radially out through the absorbent to the edge of the clear bucket and condensing face. The clean gas will then pass back into the right lung to be rebreathed. During this final step the clean gas passes over the sensing faces of three galvanic sensors that analyze the oxygen content of the gas and report to the electronics.

The electronics take the readings from the three sensors and vote between the readings and the pre-selected set point. This information is then used to control the addition of oxygen as required into the breathing loop. The data is also displayed on the primary display.

Oxygen injection occurs into the expired gas manifold, prior to the scrubber, so that the oxygen is forced through the absorbent before entering the inhalation cycle, thus aiding gas mixing.

A manual oxygen override exists, mounted on the lower inside wall of the left (exhalation) lung and this may be used to fly the system manually, or to rapidly assist the breathing loop to regain set point after an accidental gas loss or mask clear.

Diluent is admitted directly into the loop as a result of increases in hydrostatic pressure. As the ambient pressure on the system increases causing the counterlungs to collapse, a combination automatic/manual diluent addition valve is activated which automatically adds sufficient gas to return the loop volume to ambient pressure. This combination valve is sited at the top of the right (inhalation) lung.

At all times during operation the diver has access to an ON/OFF system switch, the gas supply cylinders, integrated Air II open circuit bailout and manual override features of the unit.

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Disclaimer- Prices and specifications of products presented are subject to change without notice. PRISM Topaz and the "diver guy" are trademarks of and copyright 1999 by Steam Machines, Incorporated and may not be reproduced without the express written permission of Steam Machines, Inc.