Alternative Solutions
The pony bottle is a source of redundancy by providing an alternative source of breathing gas for the diver as an effective backup to his/her primary gas supply in the event of failure of the primary system. The pony bottle is intended for use in "bail out" situations – situations in which the dive must be aborted and safe return to the surface must be facilitated. There are several alternative solutions to providing such a redundant gas supply for bail out purposes which are in common use in diving. These alternatives are listed in the following table along with a critique on how these solutions compare with pony bottle usage as a backup system:
| Alternative air source | Comparative functionality |
|---|---|
| Octopus | The octopus is an additional redundant second stage regulator taken off the existing first stage regulator and existing primary air supply. Because of this, a failure of the first stage regulator or the exhaustion of the gas supply from the primary tank makes this solution inferior to a totally redundant breathing gas system such as a pony bottle. |
| H and Y pillar valves | The primary tank can be fitted with a valve with two separate controllable outlets, both of which can mount its own first stage regulator. One outlet is connected to the primary second stage regulator, the other to the octopus. This eliminates the danger of failure in a single first-stage system. It does not mitigate the risk of loss of breathing gas from the single primary gas supply. |
| Doubles | Using a twin tank system with isolating manifold provides full redundancy in gas supply as well as the ability to isolate any faulty components which might be leaking away breathing gas. Doubles also provide much greater capacity than pony bottles. However, because the gas in the system is also for use during the dive itself it requires that the diver pays extra attention to gas management to ensure that an adequate amount of reserve is available for any bailout requirement at any phase of the dive. However, if the second tank only serves the purpose of bailout, the diver is burdened with considerable extra bulk and weight which is not required in a smaller pony bottle system. |
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