Regarding instrument valves
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Hello, fellow marine engineers: I have a question. There is a tank on site, and it is necessary to run a pipeline from the main 7-degree chilled water inlet pipe at the site to this tank. A control valve needs to be installed on this pipeline in order to regulate the liquid level in the tank. There is no on-site level gauge for this tank, but there is a pressure transmitter whose signal is sent to the DCS. What type of control valve should be installed, and how can signals be sent to operate this valve? Thank you (I’m not a specialist in instrumentation; my supervisor has asked me to draw some simple diagrams now). I’d like to ask everyone for some advice.)
Is the transmitter a level signal? If possible, a interlock valve can be used to control the opening and closing based on the high and low liquid levels
Is the transmitter a level signal device, or is it an instrument valve that transmits signals from the transmitter? Should it be a pneumatic valve or an electromagnetic valve? Thank you
If it is an open system, a pressure transducer installed in the container can be used to measure the liquid level (provided that it is installed above the area to be measured). If there are air pipelines, pneumatic valves can be used; otherwise, electric valves can be chosen. Generally, signals are not transmitted from the transducer to the control valve (*commonly referred to as a regulating valve); instead, a separate connection to the DCS control output module is required. Generally, for liquid inlet control, a pneumatic/open or electric/open valve is chosen, while for liquid outlet control, a pneumatic/close or electric/open valve is used.
First, the level signal needs to be monitored. If the pressure transmitter on site is used to measure the level, and the DCS has PID control output channels, then it is sufficient to purchase an electric control valve. The level signal collected by the transmitter is processed by the DCS to generate a 4–20mA control signal, which is then used to control the valve and regulate the level.
This post was last edited by zxb1990 on 2016-3-27 at 22:56. First, a level transmitter is installed on the tank, and then a pneumatic control valve is placed on the inlet pipeline. The signal from the level transmitter is sent to the DCS, and together with the control signal from the valve, this forms a PID control loop. The opening degree of the valve is adjusted between 0% and 100% based on the 4-20MA signal output by the level transmitter. If the user only wants to control whether the valve is open or closed, an electromagnetic valve needs to be added to the valve. Additionally, upper and lower level limits must be set; in the DCS, the values measured by the transmitter are compared with these limits, and two digital signals are generated to control whether the electromagnetic valve is powered on or off, thereby controlling the open/closed state of the valve.
The last edit to this post was made by FightingNow on 2016-3-28 at 01:31; it might seem complicated to you! Simply put, to control the liquid level, one must first be able to measure it; install a remote transmitter for liquid level measurement based on the actual conditions 2: Install manual valves, control valves, and bypass valves at appropriate locations on the inlet pipes! The control valve and the remote level gauge work together with the control system to achieve automatic control! …… 3: For the diagram format, just refer to the standard instrument flowchart! 4: The type of level gauge to use depends on the actual conditions of your tank – differential pressure level gauges (with pressure tapping points at the top and bottom), ultrasonic level gauges (with an installation point on the tank top). Control valves can be pneumatic or electric; are there any special requirements regarding explosion protection?