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Ram preventers have two packing elements on opposite sides
that close by moving toward each other. Pipe rams have
semicircular opening which match the diameter of pipe sizes for
which they are designed. Thus, the pipe ram must match the size
of the pipe currently in use. If more than one size of drill pipe is in
the hole, additional ram preventers are used in the BOP stack.
Rams designed to close when there is no pipe in the hole are called
blind rams. Blind rams will flatten the drill pipe if inadvertently
closed when the drill string in the hole but will not stop the flow
from the well. Shear rams are blind ram designed to shear the drill
string when closed. This will cause the drill string to drop from
the hole and will stop flow from the well. Shear rams are closed on
pipe only when all pipe rams and annular preventers have failed.
Ram preventers are available for working pressures of 12960,
32400, 64800 and 97200 psi.
Annular preventers, sometimes called bag-type preventers,
stop flow from the well using a ring of synthetic rubber that
contrasts in the fluid passage. The rubber packing conforms to the
shape of the pipe in the hole. Most annular preventers also will
close an open hole if necessary. A cross section of one type of
annular is shown on fig. 12.2. Annular preventers are available for
working pressures of 12960, 32400, and 64800 psi.
But the ram and annular BOPs are closed hydraulically. In
addition, the ram preventer has a screw-type locking device that
can be used to close the preventer if the hydraulic system fails. The
annular preventers are designed so that once the rubber element
contacts the drill string; the well pressure holds the preventer
closed.
Modern hydraulic systems used for closing BOP’s are high
pressure fluid accumulators similar to those developed for aircraft
fluid control systems. The accumulator is capable of supplying
sufficient high pressure fluid to close all of the units in a BOP
stack at least once and still have a reserve. The accumulator is
maintained by a small pump at all times, so the operator has the

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