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| Title: | A DEMAND REGULATED GAS MIXING SYSTEM FOR RECIRCULATING UNDERWATER BREATHING APPARATUS. |
| Authors: | Morrison, JB |
| Keywords: | DIVING
DIVER EQUIPMENT
BREATHING APPARATUS
gas mixing
rebreather |
| Issue Date: | 1990 |
| Publisher: | Undersea and Hyperbaric Medical Society, Inc. |
| Citation: | Undersea Biomedical Research, Vol. 16, No. 1 Supplement, March 1990 |
| Abstract: | When diving with special gas mixtures, open circuit demand breathing apparatus provides a low efficiency resulting in excessive gas wastage. Gas recovery using push-pull systems presents problems of logistics and diver encumbrance. Recirculating apparatus can provide a higher efficiency and reduce the dimensions of the umbilical supplying the diver. This paper presents a new concept of pneumatically controlled gas mixing for recirculating underwater breathing apparatus. The system integrates a demand dosage with a constant P02 gas mixture and offers substantial improvements in efficiency. It is based on the physiological principles that (a) the P02 of the gas mixture injected must be held constant over a large range of depths; (b) the 02 dosage must vary in response to diver work rate, and (c) diver work rate is linearly related to ventilatory demand. Oxygen and inert gasses are supplied to the apparatus from separate sources. The O2 supply is regulated such that the mass of O2 injected is directly proportional to the ventilation of the diver. The O2 is then mixed with inert gas supplied on demand and the resultant mixture is regulated so that it represents a constant fraction by volume of the diver's ventilation. Thus the PO2 of the supply gas mixture remains constant and independent of depth, whilst the dosage rate varies with diver work rate. The output of this system was modelled and compared with the performance of pneumatically controlled gas mixing systems proposed by Morrison (1972) and Payne (1978). The system was found to be 3 to 4 times more efficient than at depths of 25 to 500 m. At 300 - 500 m. the efficiency of gas utilization was calculated to be 4%, which is similar to that of normal breathing at 1 ATA. Due to its low gas utilization the design provides a practical alternative to conventional breathing systems, both as a primary apparatus with umbilical supply and as a self contained bail-out system. Details of gas mixing theory, system design, boundary parameters, and sample calculations are presented. |
| Description: | Abstract of the Undersea and Hyperbaric Medical Society, Inc. Joint Annual Scientific Meeting with the International Congress for Hyperbaric Medicine and the European Undersea Biomedical Society held 11-18 August 1990. Okura Hotel, Amsterdam, The Netherlands (http://www.uhms.org) |
| URI: | http://archive.rubicon-foundation.org/7291 |
| Appears in Collections: | UHMS Meeting Abstracts
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