Upstream vs. Downstream: What Makes Poseidon Regulators Unique

HERODIVER

The Bottom Line: The second stage of every scuba regulator contains a valve that opens in one of two ways – downstream, which opens in the direction of the airflow, or upstream, which opens against the airflow. Most regulators on the market are downstream, meaning that in the event of a malfunction, they go into free flow, ensuring the diver continues to receive air.

When discussing scuba regulators, most divers are familiar with the terms "first stage" and "second stage", but few know that hidden within the second stage is a fundamental engineering decision: whether the valve is upstream or downstream.

מערכת נשימה Poseidon Xstream | Poseidon | Herodiver

Poseidon's Uniqueness: Upstream + Servo Technology

Poseidon is the leading manufacturer in the market producing upstream regulators – which are more resistant to free flow and excel in demanding breathing systems. Poseidon, a Swedish manufacturer founded in Gothenburg in 1958, built its entire regulator philosophy around the upstream valve.

This choice is combined with unique servo technology and an Over Pressure Valve (OPV) that mitigates the risk to the diver during a malfunction.

  • What is a Downstream Valve?

    In a downstream valve, the moving part opens in the same direction the air flows and is held closed by a spring. When you inhale, a vacuum is created in the second stage that pulls the valve open.

    The Main Safety Advantage: If the first stage fails and delivers excess pressure, it pushes the valve open – resulting in a free flow of air. The diver continues to breathe.

  • What is an Upstream Valve?

    In an upstream valve, the moving mechanism acts against the pressure and opens in the opposite direction of the airflow. This design is more resistant to wear and less prone to free flow.

    But there is a catch: Excess pressure pushes the valve closed. Therefore, it must include an Over Pressure Valve (OPV) that vents the excess pressure.

How Does the Servo Work?

The servo can be compared to power steering in a car. The valve consists of two parts: one tiny valve that controls a larger valve. The small valve requires minimal force to open – and upon inhalation, a slight "tilt" of the diaphragm opens it.

This, in turn, releases the large valve, which supplies a massive amount of air. The result: incredibly low Work of Breathing (WOB), even at great depth.

  • Why Does This Matter?

    • Effortless Breathing at Depth: Provides a massive and consistent airflow with minimal effort, holding the European standard for diving to 200 meters.
    • No Adjustment Knobs: No need for a venturi switch or an adjustment knob – the system regulates itself.
    • Ambidextrous Second Stage: Can be routed from either the left or the right, an advantage in sidemount diving.
    • Field Maintenance Without Tools: The second stage can be disassembled and cleaned without a toolbox.

Important to Know

Poseidon's design is different and therefore requires familiarity. The OPV is a critical safety component, and the regulator demands service and maintenance solely by a certified Poseidon technician using only original parts. Those seeking exceptional performance in cold water and at depth – will receive an exceptional tool.

Who is Poseidon For?

  • Minimal Effort


    Divers looking for minimal breathing effort at any depth.

  • Cold Water & Tech


    Cold water and technical divers executing deep dives.

  • Engineering


    Those who appreciate unique engineering and guaranteed reliability.

Get Your Poseidon

Herodiver is the official importer of Poseidon in Israel, with technician services available both at the Lee-Yam club in Mikhmoret and the Ahla club in Eilat. Browse our selection of Poseidon regulators in our store.

The author is a sea lover with 18 years of diving experience. A mechanical engineer, diving instructor in Israel and abroad, and the founder of HERODIVER.

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