Poseidon Xstream Regulators

The demand valves found in scuba second stages can be either upstream or downstream design. In a downstream valve, the moving part of the valve opens in the same direction as the flow of gas and is kept closed by a spring. In an upstream valve, the moving part works against the pressure and opens in the opposite direction as the flow of gas. The upstream design is less likely to experience problems caused by wear and more resistant to free flow, but most scuba second stages are downstream design. If the first stage fails and delivers excessive pressure to the second stage, a downstream valve is forced open resulting in a free flow and rapid loss of breathing gas. With an upstream valve, the result of over pressurization usually means the valve is forced closed. This will stop the free flow but unless the over pressure is relieved it may cause another failure such as a hose rupture or loss of buoyancy control. This means that regulators with upstream second stages must always incorporate an over pressure relief valve (OPV) in their design. The OPV allows the diver to continue to breathe the regulator with a minimal loss of gas.

Historically, Poseidon incorporated the OPV for their upstream second stages in a unique fitting on the end of their low-pressure second stage hose. The special hose was not widely available, particularly in the uncommon lengths preferred by technical divers. In 2008 Poseidon updated their designs (the Mk3 designation) to no longer require a Poseidon-specific low-pressure regulator hose. The OPV is now located in the Poseidon first stage, enabling use of a standard hose of any length and allowing use of a hose swivel or angle adapter if desired. We offer a M31-1.5mm = 9/16-Inch Adapter that will convert any length standard LP regulator hose for use with older (Pre-2008) Poseidon second stages, when also used with an add-on OPV.