Expandable plug and control method

In an method of maintaining a desired pressure differential .DELTA.P across an inflatable plug positioned within a tube of internal diameter d with relative movement between the plug and the tube, while allowing controlled leakage past the plug of a lubricating flow of fluid within the tube, the improvement which comprises inflating the plug by applying and maintaining an internal pressure P.sub.p in the plug substantially according to the equation

• P.sub.p =.DELTA.P+P.sub.d
• wherein P.sub.d is the internal pressure required to expand the plug to tube diameter d without confinement.

In a method of maintaining a desired pressure differential .DELTA.P across an inflatable plug positioned within a tube of internal diameter d, the improvement which comprises inflating the plug by applying and maintaining an internal pressure P.sub.p in the plug substantially according to the equation

• P.sub.p =.DELTA.P+P.sub.d
• wherein P.sub.d is the internal pressure required to expand the plug to tube diameter d without confinement.

A tube having located therein an inflatable plug for regulating pressure or flow within the tube, the inflatable plug comprising an inflatable bladder adapted for diametral expansion by application of internal fluid pressure, fluid inlet means communicating with the interior of the bladder for connection to a source of inflating fluid and reinforcement means including a plurality of flexible reinforcing cords which provide axial reinforcement to the plug and diametral support to the bladder, the improvement wherein each said reinforcing cord comprises a plurality of untwisted single strands which individually redistribute over the surface of the bladder as the bladder expands upon inflating, toward the tube, whereby to allow controlled leakage past the plug of a lubricating flow of fluid within the tube, whilst maintaining a continuous coverage of the bladder so as to prevent cutting of the bladder by the cords.

A tube having located therein an inflatable plug for regulating pressure or flow within the tube, the inflatable plug comprising an inflatable bladder adapted for diametral expansion by application of internal fluid pressure, fluid inlet means communicating with the interior of the bladder for connection to a source of inflating fluid and reinforcement means including a plurality of flexible reinforcing cords which cross each other in opposing helix directions around the bladder and which provide axial reinforcement to the plug and diametral support to the bladder, the improvement wherein each said reinforcing cord comprises a plurality of untwisted single strands which individually redistribute over the surface of the bladder as the bladder expands upon inflation towards an internal surface of the tube, to allow controlled leakage past the plug of a lubricating flow of fluid within the tube.

A tube having located therein an inflatable plug for regulating pressure or flow within the tube, the inflatable plug comprising an inflatable bladder adapted for diametral expansion by application of internal fluid pressure, fluid inlet means communicating with the interior of the bladder for connection to a source of inflating fluid and reinforcement means including a plurality of flexible reinforcing cords which provide axial reinforcement to the plug and diametral support to the bladder, the improvement wherein a high number of fine, compliant strands are provided and which offer little or no resistance to diametral expansion of the bladder, upon inflation of the bladder towards an internal surface of the tube, to allow controlled leakage past the plug of a lubricating flow of fluid within the tube.