1. Field of the Invention
This invention relates, generally, to devices for flow control, and particularly to flow control devices which can be remotely controlled.
2. Prior Art
Flow control devices are used in many industrial applications. Gate valves, ball valves, check valves, needle valves, and many other types of flow control devices are used in various industrial processes. A common configuration for a flow control device used in a industrial process is to have a flow control device located in a flow stream. The valve will include an actuator which is usually powered by compressed air.
The compressed air actuator on the valve will be activated by a control system which is electronically linked to a remote control station. This remote control station is usually a control room which monitors the process and controls the many flow control devices in the process.
There are two power systems necessary to run the conventional compressed air actuated valve. The first power system is the compressed air. Most petro-chemical facilities have a vast compressed air system running throughout the facility to supply compressed air to valve actuators and other equipment. The second power system is the electrical power system used for the electronic control system.
A disadvantage of compressed air actuators is that if power is lost to the actuator the valve will move to a default position, either open or closed. The inventors are not aware of actuator systems which leave the valve in the last known setting in the event that the compressed air supply is lost. Another disadvantage of compressed air actuators is that they require another piping infrastructure beyond the piping for the fluids used in the process.
Traditional control valves use a stem which traverses the casing of the valve. The section of the stem external to the valve is connected to the actuating mechanism. The section of the stem inside the valve is connected to a needle, ball, gate , disc, or some other structure which can be moved within the valve to control flow.
Regardless of the exact type of structure used in the control valve, a seal is used between the stem and casing. The goal of the seal (also known as packing) is to prevent leakage of the product in the pipe to the outside atmosphere. In applications involving negative pressure differentials, the seal prevents contamination of the product by the gases in the atmosphere.
There have been many advances in the field of flow control to improve seals. Improving the performance of seals is especially important in applications involving hazardous, corrosive, or toxic fluids. However, all of these advances in the seal do not change the basic configuration in which the stem is in contact with the product atmosphere, and moves (either vertically or by rotating) in relation to the casing.
What is needed is a flow control device which will eliminate the need for a seal between two moving parts so as prevent leakage of fluid to the atmosphere. What is also needed is a flow control device which does not require duplicate power systems. The flow control device should also be capable of remaining in the last known position if power to the flow control device is cut.