Method of and apparatus for control of saftey valves

A method of controlling safety valve means of a system, the safety valve means comprising a valve seat, a closing member, and an operating cylinder for displacing the closing member relative to the valve seat, the operating cylinder being connected to a hydraulic control circuit including at least one fast-response outflow solenoid valve and at least one fast-response inflow solenoid valve actuatable in accordance with a pressure of the system medium for guiding the hydraulic fluid out of and in the operating cylinder, respectively, to thereby control opening and closing of the safety valve means, said method comprising the steps of:

• preparing, in accordance with system characteristics, at least one characteristic line for displacing the closing member as a function of a system medium pressure and a pressure change speed dp/dt;
• storing the one characteristic line in a computer in form of one of points of the one characteristic line and coefficients of analytical functions;
• measuring the system medium pressure in a short cycle time and storing obtaining data in the computer;
• determining a pressure change speed in a cycle time and determining a dimension of a closing member stroke in accordance with the stored one characteristic line for effecting one of stepwise opening and closing of the safety valve means;
• determining a quantity of the hydraulic fluid to be communicated through one of the outflow solenoid valve and the inflow solenoid valve per cycle to effect a respective stroke of the closing member;
• determining electric opening pulses for actuation of the one of the outflow and inflow solenoid valves in accordance with the determined quantity of the hydraulic fluid;
• amplifying the electric opening pulses;
• and
• communicating the amplified electric opening pulses to the one of the outflow and inflow solenoid valves, the one of the outflow and inflow solenoid valves controlling the one of the opening and closing of the safety valve means in small steps at a low pressure change speed, in large steps at a high pressure change speed, and in a single step at a very high pressure change speed until an end of the closing member stroke.