This adapter works on both modern and vintage Poseidon Xstream and Jetstream second stage regulators. Historically, Poseidon incorporated the OPV for their upstream second stages in a unique fitting on the end of their non-standard low-pressure second stage hose. The special hose is 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.

To use this adapter with Poseidon Jetstream second stage regulators manufactured prior to 2008, you MUST either add a first stage regulator OPV to an unused LP port on your older (Pre-2008) Poseidon first stage - OR - use a current (manufactured 2008 and later) Poseidon first stage that already incorporates an OPV.