This file photo shows a view of the Deepwater Horizon blowout preventer, sitting on the sea floor above the oil well. This file photo shows a view of the Deepwater Horizon blowout preventer, sitting on the sea floor above the oil well. (BP) The Deepwater Horizon rig that exploded 80 kilometres from the Louisiana coast included a series of valves on the seabed designed to prevent a well blowout. For reasons that are still unclear, the blowout preventer didn't work when the well exploded on April 20 and the rig burst into flames.

A spokesperson for Cameron International Corp., the Houston company that supplied the blowout preventer, said Friday that he was unable to explain exactly how the equipment works.

"All of our guys who are experts on that are at the well," said Scott Amann, vice-president of investor relations.

British-based BP, the company that leases the rig and operates it, did not immediately return calls.The robotic arm of a remotely controlled submarine tries to reactivate the Deepwater Horizon blowout preventer on Thursday, April 22.The robotic arm of a remotely controlled submarine tries to reactivate the Deepwater Horizon blowout preventer on Thursday, April 22. (US Coast Guard)

Meanwhile, six remotely controlled submarines have so far failed to reactivate the valves in the blowout preventer. Now engineers are working onshore to build a dome that will be placed over the leak to collect the spewing oil and funnel it to the surface for treatment.

The system is designed for shallow water and this marks the first time anyone has tried to adapt it for deep water. BP said in a news release that it could be four weeks before the dome system is functioning.

BP is also working on an even longer-term solution. It has already moved a drilling platform to the area and plans to drill a relief well that will decrease pressure on the original well and inject a sealant into the well to plug it. That effort is expect to take two to three months, the company says.

This grapic shows the current state of the Horizon rig. On the left is the relief well that BP proposes to drill. On the right is the existing well that Horizon tapped. The Horizon rig is shown on the sea floor where it sunk after it exploded. The ROVs are the submarines trying to reactivate the blowout preventer valve and shut off the leak. This grapic shows the current state of the Horizon rig. On the left is the relief well that BP proposes to drill. On the right is the existing well that Horizon tapped. The Horizon rig is shown on the sea floor where it sunk after it exploded. The ROVs are the submarines trying to reactivate the blowout preventer valve and shut off the leak. (BP)