... or dual-wing 4Positive or adjustable choke Wellhead produced by BH mainly comprise split type wellhead,integral type ... tree adopts a hidden bar,namely a seal structure behind the valve,thereby having the characteristics of small ... property,etc.,the tubing hanger extending neck is sealed by 'SBMS'metal.Nominal pressure of the metal seal ... 6A oil and gas drilling equipment eucalyptus trees X-mas Tree