【Weekly 3 Questions, Question 13】2017.09.07
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By replying to bg9.png, you can see the answer to the previous question. (Single-choice question) In a cascade control system composed of furnace temperature and fuel oil flow rate, the furnace temperature is the primary parameter while the fuel oil flow rate is the secondary parameter. If gas-operated valves are used, the correct combination for the primary and secondary controllers is (D). A. Primary controller – direct action, secondary controller – direct action; B. Primary controller – direct action, secondary controller – reverse action; C. Primary controller – reverse action, secondary controller – direct action; D. Primary controller – reverse action, secondary controller – reverse action. The question for this session is as follows: (Essay question) How to operate the instrument three-valve assembly? The answer will be revealed in the next issue; by answering the question in that issue, you will be able to see the answer. Thank you! —————————————————————————————————————————————————————————————— Scoring criteria: 2 Wealth points for incorrect attempts; 3–6 points for *incomplete* answers; 8 Wealth points for correct answers with detailed explanations; 10–15 Wealth points for correct answers along with supplementary *answers*. Please score according to these criteria. Note: If there are editing records after answering, only those who participated will be credited points. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters that have nothing to do with the answer are all considered malicious spamming; points will start to be deducted after three warnings
1. When operating the three-valve instrument group, two principles must be observed: (1) The condensate or isolation fluid in the pressure guiding tube must not be lost. (2) The measuring element (diaphragm box or bellows) must not be subjected to compressive force or heat in one direction only. 2. The startup sequence for the three-valve assembly should be: open the positive pressure valve, close the balance valve, and open the negative pressure valve. 3. The shutdown sequence for the three-valve assembly is the opposite of the above: close the negative pressure valve, open the balance valve, and close the positive pressure valve. Furthermore, for steam flow meters and level gauges with negative migration, it is not allowed for the positive and negative pressure valves as well as the balance valve to be open simultaneously during the startup or shutdown of the three-valve assembly, even if for a short period of time. With all three valves open, the condensate or isolation fluid in the negative pressure side condenser will be lost, resulting in inaccurate instrument readings and even forcing a shutdown of the system.
I. When operating the three-valve instrument group, two principles must be observed: (1) The condensed water or isolation fluid in the pressure guiding pipe must not be lost. (2) The measuring element (diaphragm box or bellows) must not be subjected to compressive force or heat in one direction only. II. The startup sequence for the two or three valve assemblies should be: open the positive pressure valve, close the balance valve, and open the negative pressure valve. III. The shutdown sequence for the three-valve assembly is the opposite of the above, that is: close the negative pressure valve, open the balance valve, and close the positive pressure valve.
Open the balance valve, slowly open the positive pressure valve, close the balance valve, open the negative pressure valve; exiting involves reversing these operations.
When operating the three-valve instrument cluster, two principles must be observed: (1) The condensate or isolation fluid in the pressure guide tube must not be lost. (2) The measuring element (diaphragm box or bellows) must not be subjected to compressive force or heat in one direction only. B. The startup sequence for the three-valve assembly should be: open the positive pressure valve, close the balance valve, and open the negative pressure valve. C. The shutdown sequence for the three-valve assembly is the opposite of the above, that is: close the negative pressure valve, open the balance valve, and close the positive pressure valve. Furthermore, for steam flow meters and level gauges with negative migration, it is not allowed for the positive pressure valve, negative pressure valve, and balance valve to be open simultaneously during the startup or shutdown of the three-valve assembly, even if such a situation lasts only for a short time. With all three valves open, the condensate or isolation fluid in the negative pressure side condenser will be lost, resulting in inaccurate instrument readings and even forcing a shutdown of the system.
A. When operating the three-valve instrument panel, two principles must be observed: (1) The condensed water or isolation fluid in the pressure guiding tube must not be lost. (2) The measuring element (diaphragm box or bellows) must not be subjected to compressive force or heat in one direction only. B. The startup sequence for the three-valve assembly should be: open the positive pressure valve, close the balance valve, and open the negative pressure valve. C. The shutdown sequence for the three-valve assembly is the opposite of the above, that is: close the negative pressure valve, open the balance valve, and close the positive pressure valve. Furthermore, for steam flow meters and level gauges with negative migration, it is not allowed for the positive and negative pressure valves as well as the balance valve to be open simultaneously during the startup or shutdown of the three-valve assembly, even if for a short period of time. With all three valves open, the condensate or isolation fluid in the negative pressure side condenser will be lost, resulting in inaccurate instrument readings and even forcing a shutdown
Open the positive pressure valve, close the balance valve; open the negative pressure valve, and close the one that is opposite to it
1. At startup: Open the pressure-taking valves on both sides, then slowly close the connection valve. 2. During removal, open the connection valve, and then slowly close the pressure-taking valves on both sides
The sequence of opening is: open the positive pressure valve, close the balance valve, and open the negative pressure valve. The sequence for shutting down is: close the negative pressure valve, open the balance valve, and close the positive pressure valve. Note: When there is condensation in the pressure guiding pipe, it is strictly prohibited to have all three valve assemblies in the open position at the same time.
Close the negative pressure valve, open the balance valve, and close the positive pressure valve. (Disabled) When in use, open the positive pressure valve, close the balance valve, and open the negative pressure valve. When an isolation fluid is present, it is necessary to ensure that the three valve assemblies are not opened simultaneously, in order to prevent the isolation fluid from escaping due to pressure differences.