A few questions about split-range control? Is it definitely a gas shut-off valve going downward?
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Similarly, is a line tilted 45 degrees downward necessarily a gas shut-off? Why?
\"Gas off\" means the air control valve is closed; \"Emergency on\" should be FO. Well, what if I happen to be controlling it in the opposite way? If the line slopes downward at 45 degrees, then it must be gas on – isn’t that possible?
On the graph, the vertical axis represents the valve opening degree, while the horizontal axis represents the air pressure applied to the valve. The 45° downward slope clearly shows that as the signal increases, the valve opening degree decreases; thus, it is the air pressure that causes the valve to close, which is why it is an air-operated valve!
This post was last edited by HEJIYUER on 2021-12-5 22:47, version 1. This of yours is used to control the split line. The AO control signal Vs controls the valve opening degree. The X-axis represents the magnitude of the diaphragm head pressure; since positioners are generally of the positive-type, the horizontal axis can be considered as representing the value of AO (4-20mA), rather than the value of the process measurement PV. Increase in AO = increase in air pressure, but the opening of the Y-axis decreases; therefore, it is a FO valve. 2. If the X-axis represents the value of a process parameter PV, such as the sealing pressure, this is called a process requirement profile. As PV increases from left to right on the X-axis, the pressure valve moves from fully open to the set point to 0% closed position ； The pressure relief valve moves from fully closed to fully open in a V shape, passing through the 0% setpoint. The sequence and direction of operation for the two valves are determined by the process requirements, and are unrelated to the forward/reverse or FO/FC settings of the controller. 3. Based on the process demand split diagram for Process 2, by selecting the forward/reverse mode of the controller and taking into account FC/FO, the control split line for 1 can be determined. No matter how you design the sequence of steps, the final valve action must meet the requirements of 2; this is an essential requirement. The test is simple: set the DCS to automatic mode, manually increase the PV value from low to high, and check whether the valve operates as specified; if not, reverse the AO output.