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This kind of rubber is just like a half ball . It is made of radial supporting ribs (steel
segment) and rubber. The rib is made of alloy－steel. When the rubber is opened, the ribs will be away
from the hole to return to original position. Even if the rubber is worn seriously, it will not block the hole.
Turn over of the rubber is limited. When a hole is closed, the pressure of the hole forces the rubber
turn over, but the steel segment can resist the turn over, causing the rubber being at safe status. So it
can stand high pressure without damage.
Funnel effect. During tripping out, well pressure and pipe movement are in the same direction.
Rubber compresses firmly against the steel segment at the top of the element, but rubber at the bottom
is slightly compressed. This creates a “funnel effect” that makes it easy for a tool joint to enter the sealing
element. When tripping in, well pressure and pipe movement oppose each other. Well pressure
compresses the rubber portion of the element against the steel segments as the tool joint moves down
into the element. This prolongs the life of the rubber.
Large reserve of rubber: This kind of seal element has more rubber than others. When it is worn
during tripping there is more spare rubber for replenishment. So it is especially suitable to use at floating
vessel. With long service life, tripping in deep well can be carried out without changing seal element.
Well pressure assists the closing of the sealing element. This makes the element’s sealing more
tight and reliable.
The steel segments molded into the rubber make metal-to-metal sliding contact with the sphere of
the housing. This provides lower coefficient of friction than rubber-to-metal contact would. So the closing
pressure is reduced.