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To provide 100% redundancy in the BOP control, an identical control

system is installed on the stack 180° from the other control pod and receptacle. In

the event of hydraulic control failure through one hose bundle and control pod, the

other system may be actuated.

Hydraulic power can be directed to a function from either control pod

through shuttle valves mounted on the operating functions of the BOP. Two inlets

to the shuttle valve are connected to the hoses from the female receptacles of the

hydraulic control system. Inside the body of the shuttle valve, a sealing shuttle

piston moves with operating pressure from inlet to inlet, directing the hydraulic

fluid to the outlet connected to the function.

When a BOP stack employs a single female system for control, the female

receptacles are mounted on the upper frame of the BOP. The male control pods

lock and seal in the female receptacles and are run with the stack. The individual
control pods and hose bundles of a single female system can be retrieved

independently and rerun to the BOP stack with the use of a small guide frame that
is run on two guidelines. To release the riser from the stack in an emergency

situation, the riser connector and both control pods must be released.
The support equipment for the hydraulic control system consists of two

power-driven hose reels that spool off and rewind the control hose bundle, a master

control panel with hydraulic pumps and fluid supply reservoirs, and a driller's

control panel. Often a mini-panel is included in the toolpusher's office. The

regulated output pressure from the master panel is usually 1,500 psi with 3,000 psi

available.

It is now standard practice to install a rack of accumulator bottles on the

BOP stack to provide a sufficient volume of hydraulic fluid to operate all functions

on the stack. This avoids the slow reaction time that would result if all the required

fluid had to be transferred through the hose bundle down to the BOP.

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