How to understand step control
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Both are wind-operated valves; how is control achieved?
There are two control valves in the pressure vessel: one for replenishing fuel gas pressure, and the other for venting to stabilize pressure. Both are wind-operated valves. From some information I’ve seen, it seems that one valve should be used to open the wind and another to close it
The setting of the wind on/off function is determined first based on process safety requirements; to change the direction of operation, a reverser can be used
For the standard pressure-controlled intake and exhaust timing, the fourth set of curves should be selected
Why are all valves operated by air? How can they be controlled in that case? When the pressure is high, they should all be open. The fourth valve is one that operates on air shut-off principle and another that operates on air open-principle; I can understand that
Both use air to open the valves and are set to a closed position in case of failure, posing a safety risk. As for step-by-step adjustment, I think it has nothing to do with turning the gas on or off.
Step control refers to the valve position being set according to a predetermined curve; the open/closed positions in response to air supply are the valve positions in the event of a gas supply failure, and they aren’t very important
The 6th floor is correct; the activation and deactivation of gas have nothing to do with the control method, but rather relate to the process and safety aspects – it is the process that dictates this. It is reasonable to choose 4 for step control; however, both are air-actuated valves, and if the air supply is lost, won’t everything get emptied? What a waste... It’s also determined by the manufacturing process; we can only give suggestions.
What really surprises me is that the inlet and outlet for air intake and exhaust use DN150, while the inlet and outlet of the container use DN50, and the safety valve uses DN200 – what kind of usage is this?
To be precise, this is not considered standard proportional control. The segmented control room divides the 4–20mA signal into several segments, with each segment being sent to a control valve. In this example, it is a pressure signal that is sent to two pressure controllers, with each pressure controller sending the signal to its own control valve. It is speculated that the set values of the two pressure controllers are different; perhaps PIC-10301A is a positive-action controller whose set signal is on the low side. As the pressure measurement signal increases, its output decreases, resulting in a reduced perfusion flow and a drop in pressure ； PIC—10301B is a feedback controller; its setpoint is relatively high. As the pressure measurement signal increases, its output rises, the exhaust flow increases, and the pressure decreases ； To this end, it is adjusted by PIC—10301A when the pressure is low, and by PIC—10301B when the pressure is high.
Achieving control is not a problem; it depends on the safety of process control.