Improvements in flotation means for subsea well riser wherein the riser is run from a floating vessel and includes one or more buoyancy chambers open in the lower portions thereof to the sea and a gas injection line runs from the vessel to each of the chambers for injecting gas from a source thereof under pressure into each such chamber. The improvements include the provision of means for controlling the bleeding off of gas from within each of the chambers to reduce the buoyancy thereof thereby making the flotation of the riser completely adjustable. A check valve may be provided between the injection line and the chambers for limiting the introduction of gas into the chambers from the injection line until a predetermined pressure of the gas in the injection line is reached.
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