Safety valve control system for production well

In a safety system for closing a primary valve disposed in the flow path of a primary fluid, in response to an indication of an undesirable condition from a monitoring device, the opening and closing of the primary valve being controlled by the pressure of an operating fluid supplied thereto, the system being composed of input means arranged to be connected to the monitoring device to receive therefrom an indication of the condition being monitored, output means arranged to supply operating fluid to the primary valve, valve means connected with the output means for controlling the pressure of the operating fluid at the output means, and fluid-responsive operator means having an input operatively associated with the input means for receiving a control fluid, the operator means being connected to the valve means for switching the valve means between a state which causes the pressure at the output to effectuate opening of the primary valve and a state which causes the pressure at the output to effectuate closing of the primary valve, the pressure of the control fluid at the operator means when an indication of an undesirable condition is present at the input means having a value which causes the operator means to switch the valve means into the state which causes the operating fluid pressure at the output means to effectuate closing of the primary valve, the improvement wherein:

• said system comprises conduit means connected to establish direct fluid communication between said operator means input and said input means, such that control fluid is present at said input means;
• the control fluid pressure at said input means is determined by the indication received from the monitoring device;
• said operator means are arranged to switch said valve means into the state which results in closing of the primary valve when the control fluid pressure at said operator means input corresponds to the control fluid pressure created at said input means when an indication of an undesirable condition is received from the monitoring device;
• said valve means and operator means comprise a first valve having an associated operator and presenting a normally closed fluid passage, and a second valve having an associated operator and presenting a normally open fluid passage;
• and said system further comprises a source of operating fluid at a pressure whose value is sufficient to effectuate closing of the primary valve, and fluid-driven pump means connected between said source and one side of the passage defined by said first valve, said pump being arranged to provide, at its output, operating fluid at a pressure sufficient to effectuate opening of the primary valve, with the other side of the passage defined by said first valve being connected to said output means and to one side of the passage defined by said second valve, and the other side of said passage defined by said second valve being connected to said source.