Fluid handling – Processes – Involving pressure control
Patent
1988-06-03
1990-03-27
Cohan, Alan
Fluid handling
Processes
Involving pressure control
1374875, 13762411, G05D 1600
Patent
active
049111922
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a method of and an apparatus for control of safety valves in which a closing member is pressed against a valve seat against pressure of a medium under an action of an operating cylinder connected to a hydraulic control circuit, and in which, in order to achieve a valve opening lift, one or more outflow pressure sensor controlled solenoid valves open to enable a hydraulic fluid flow from the operating cylinder when the set pressure is reached. The solenoid valves close again when the pressure falls below the set pressure, whereby hydraulic fluid is supplied to the operating cylinder to effect valve closing.
In a known control method of this kind for safety valves, the operating cylinder constantly communicates with the pressure line of the hydraulic control circuit via a throttle. When the set pressure is reached, pressure switches open the outflow solenoid valves and keep them open until the medium pressure falls below a switching threshold of the pressure switches. Because of the continuously available load pressure, hydraulic fluid flows into the operating cylinder after the closing of the solenoid valves and closes the safety valve again.
A disadvantage in this known control device is that solenoid valves which are arranged in a redundant manner must have a valve opening area adapted to the highest pressure rise speed of the medium. Therefore, when the pressure rise is very slow, an excessive quantity of the medium to be secured is guided out and excessive pressure drop in the medium and high medium losses can accordingly occur. These pressure surges run through the pipeline as a pressure wave and lead to shaking of the safety valve and the pipeline. The pressure waves can also reach the pressure switches, so that the safety valve then continuously opens and closes in an undesired manner. In this known control device, the opening and closing of the safety valve is effected in accordance with an opening speed determined by the hydraulic system, and it is not possible in this case to adapt to an another opening and closing characteristic. Since the hydraulic pressure is continuously available at the operating cylinder via the throttle, the safety valve is closed again after every closure of the outflow solenoid valves, and permanent intermediate positions of the valve closing member are not possible. Therefore, this safety valve must continuously open and close when partial quantities are guided out.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a method of and an apparatus for controlling safety valves in which the safety valve quickly guides out large quantities of medium at high pressure rise speeds in cases of danger, but which opens only wide enough and long enough during a slow pressure rise as required to guide out a small quantity of medium necessary for compensating the slight pressure rise. Opening and closing behavior of the safety valve is adaptable to respective conditions of the system at all times.
In order that characteristic lines for the stroke of the valve closing member which are adapted for the widest range of system conditions be prepared, electronically stored and converted into stroke steps in a computer, one and the same safety valve can be used for the widest range of systems merely by inputting other stroke characteristic lines. Since the medium pressure is measured in short intervals, the smallest change in pressure can be recognized in the computer, and this change in pressure can be used to guide out the smallest quantities of hydraulic fluid, so that the valve opening process can be effected in many small partial opening steps. If, in so doing, the pressure change speed approximates zero, the safety valve remains in the achieved lift position and continuously guides out the excess quantity. By this sensitive adaptation, which is achieved by stepwise opening or closing of the safety valve, pressure surges, such as occur in known valves because of an excessively large opening lift, are
REFERENCES:
patent: 3665945 (1972-05-01), Ottenstein
patent: 4550747 (1985-11-01), Woodworth
patent: 4694390 (1987-09-01), Lee
patent: 4720807 (1988-01-01), Ferran
Hartfiel Johannes
Schmitt Manfred
Cohan Alan
Striker Michael J.
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