In standard valves, when it is given a command to open to a certain point, there is no feedback to verify that the valve has opened to that position. With a valve positioner, the command is given and the valve positioner reads the opening, verifying the position and readjusting until it gets it to the exact position needed. This allows for great precision in the adjustment.
In addition to the valve positioners, valve products themselves deserve our attention. There are many categories. Among all those valve types, the check valve is one of the main types. It is used to close off piping and to prevent backflow. Backflow occurs when the substance in the pipe flows in the opposite direction when the valve is closed. There are many forms of this type of valves such as ball check valves, stop-check valve, cone check valves, and disk check valve and so on.
The first category is the most common one. A ball in the shell of the valve fits neatly against the side of the valve where the water comes in. Water pushing through the pipe moves the ball against the spring, allowing water through the valve. When the water is turned off, the ball is pushed into place by the spring and keeps water from flowing back through the pipe.
The second type is a product with override control to stop flow regardless of flow direction or pressure. It can not only close in response to backflow or insufficient forward pressure, but also can be significantly shut down by an external mechanism, thereby preventing any flow regardless of forward pressure.
The third one is similar to ball check valves, but the plug that seals the valve is shaped like a cone. It also can be called a lift check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. The cone is held on a bar, allowing it to lift out of the way when the water is flowing and drop back into place when the water is off. If water backflows through the pipe, it pushes up against the cone, creating a seal that keeps it from going any further.
The fourth one is the disk valve which is also known as swing check valve. It operates in the same manner as ball and cone valves, but the plug that settles over the opening is a disk. Disk and cone valves tend to wear down more because they have more moving parts and because they get bumped around on top of the flow of water when it is turned on.