Patent ID: 8387706

Claim:
A method of providing motive force for one or more rams of a subsea blowout preventer comprising providing one or more pistons connected to said one or more rams, said pistons having a distal side and a proximate side with respect to said rams, providing a tank to contain a first pressure less than the ambient pressure of seawater at the location of said subsea blowout preventer, providing a control system pressure which is higher than said ambient pressure; providing at least one first valve which selectively connects said control pressure to said distal side of said pistons whereby said at least one first valve is operable for applying said control pressure to said distal side of said pistons for closing said rams; providing at least one second valve which selectively connects said control pressure to said proximate side of said pistons whereby said at least one second valve is operable for applying said control pressure to said proximate side of said pistons for opening said rams; and connecting at least one third valve which selectively connects said first pressure to said proximate side of said pistons and connects to said second valve whereby said third valve is operable for connecting said first pressure to said proximate side of said pistons for closing said rams and for disconnecting said at least one second valve from applying said control pressure to said proximate side of said pistons.