Accumulator or Koomey Unit

Accumulator or Koomey Unit: Accumulator or koomey unit is used to provide hydraulic fluid under pressure to BOP i.e. it provides the necessary force to open or close the bop. Koomey unit contains the following main parts: 

Reservoir: Reservoir contains the hydraulic fluid at atmospheric pressure. Reservoir provides the hydraulic fluid to air pump and hydraulic pump which in turn fill the accumulator. After the fluid is used to activate the BOPs, it is returned to reservoir. Hence the BOP system is a closed loop system.

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Air pump: Air pump is used to provide fluid to the accumulators. It is used to provide large of amount fluid to the accumulator at a relatively low pressure. It is operated by air and air is obtained by the pump through air supply manifold. Each pump separately takes air from the manifold and contains air filter to remove contaminants that can damage the pump, air lubricator to impregnate the air with oil to lubricate the pump during operation, air supply valve to open or close the supply of air to the air pump The hydraulic fluid suction line of pump contains suction valve to isolate the pump and suction strainer which removes any impurities present in the hydraulic fluid. The pump discharge line contains check valve which allows only one way flow. All the isolation and check valves are provided to isolate the air pump from other systems if its maintenance is required. Air pump also contains air switch which senses the pressure of accumulator, therefore when pressure reached to 3000 psi it automatically stops air supply to pump and when pressure decrease to 2900 psi it automatically starts the pump to increase the pressure. Electric pump: Electric pump is primary or additional pump source and it is used to pressurize the hydraulic fluid. It is operated by electric motor. Pump takes intake from the reservoir through suction line contains suction valve and suction strainer. The discharge line contains check valve. The function of all these valves exactly the same as these valves had in air pump. Electric pump contains electric pressure switch which automatically stop the pump when pressure reaches to 3000 psi and starts the pump when pressure reached to 2700 psi.

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Control Valve: The control valve is 1” four-way, three position shear selector type valve. They have 90˚ rotation with 45˚ dent. The control valve is provided for each ram, preventer and HCR. There is name plate indicating the name of each part for which the control valve is provided along with open and close position. The valve is either kept in open or close position. The center position blocks both function port and hence it is only used when there is pressure while operating the BOP. The valve should be operated from open to close and vice versa in swift motion, pausing will cause valve to interflow thus venting some of the fluid and delaying the function operation. Control can also be operated with air when bop is being remotely operated away from the accumulator unit.

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Accumulators: Accumulator or bottles contains the pressurized hydraulic fluid which is supplied to preventer and rams. Accumulator is bladder type whose volume is 11 gallon out of which bladder volume is 1 gallon which separates nitrogen from the hydraulic fluid. The bottle is pre charged at 1000 psi and occupies 10 gallon volume of the bottle. 1.7 gallon of hydraulic fluid is used to pre charge the nitrogen to 1200 psi which is the least operating or discharge pressure. This reduces the volume of nitrogen to 8.3 gallon. Air or electric pump then pump the fluid and increase the pressure to 3000 psi which is the maximum operating or discharge pressure and hence decrease the nitrogen volume to 3.3 gallon and liquid volume increases to 7.7 gallon out of only 5 gallon is usable. There are 32 bottles in accumulator unit and hence 160 gallon of usable hydraulic fluid is present.

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Gauges: Gauges are present to show accumulator, manifold, annular and rig air pressure.

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Regulators: Regulators present in koomey unit are manifold, annular and bypass valve regulator. Manifold and annular regulator reduces the pressure up to maximum of 1500 psi whereas bypass valve is used to supply the fluid at a pressure of more than 1500 psi and up to a pressure of 3000 psi. In normal operation it is kept in low position and allows fluid to pass through manifold and annular regulator where in high position it restricts the flow of fluid towards annular and manifold regulator and bypass them. All the regulators can be operated with air when they are being activated remotely away from the koomey unit.

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Remote Control: The koomey unit and hence the BOP can be operated remotely away from the koomey unit. There are two remote units. First is on rig floor which is called Driller’s remote control unit and second is safe distance away from the rig which is called Auxiliary remote control unit. They have buttons which through Koomey unit can be operated. They have LED installed within them to show which button is active and hence showing the actual position of control valves on koomey unit. They send signal electrical to electric panel installed on koomey unit which in turns activate the valve by sending the air towards control valve which is supplied from rig. There is a master button which must be pressed simultaneously with the required function button to perform the required function.

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Accumulator module piping: Accumulators are mounted in banks and can be isolated with isolator valves. These are kept open at all times during normal operation. If any accumulator is faulty than bank can be isolated for servicing the accumulator.

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Manifold piping: Consist of manifold header which supplies fluid all the control valve except the annular preventer control valve for which separate line is provided. These lines are provided with regulators. Separate lines are provided because pressure requirement for annular regulator and other rams are different.